Address review comments

- Add doc comment to new type
- Restore "only supported directly in conditions of `if` and `while` expressions" note
- Rename variant with clearer name

compiler/rustc_parse/messages.ftl

@@ -196,6 +196,7 @@ parse_expected_else_block = expected `{"{"}`, found {$first_tok}
     .suggestion = add an `if` if this is the condition of a chained `else if` statement
 
 parse_expected_expression_found_let = expected expression, found `let` statement
+    .note = only supported directly in conditions of `if` and `while` expressions
     .not_supported_or = `||` operators are not supported in let chain expressions
     .not_supported_parentheses = `let`s wrapped in parentheses are not supported in a context with let chains
 

compiler/rustc_parse/src/errors.rs

@@ -392,6 +392,7 @@ pub(crate) struct IfExpressionMissingCondition {
 
 #[derive(Diagnostic)]
 #[diag(parse_expected_expression_found_let)]
+#[note]
 pub(crate) struct ExpectedExpressionFoundLet {
     #[primary_span]
     pub span: Span,

compiler/rustc_parse/src/parser/expr.rs

@@ -2461,7 +2461,7 @@ impl<'a> Parser<'a> {
         let is_recovered = if !restrictions.contains(Restrictions::ALLOW_LET) {
             Some(self.sess.emit_err(errors::ExpectedExpressionFoundLet {
                 span: self.token.span,
-                reason: ForbiddenLetReason::GenericForbidden,
+                reason: ForbiddenLetReason::OtherForbidden,
             }))
         } else {
             None
@@ -3427,7 +3427,7 @@ impl<'a> Parser<'a> {
 #[derive(Clone, Copy, Subdiagnostic)]
 pub(crate) enum ForbiddenLetReason {
     /// `let` is not valid and the source environment is not important
-    GenericForbidden,
+    OtherForbidden,
     /// A let chain with the `||` operator
     #[note(parse_not_supported_or)]
     NotSupportedOr(#[primary_span] Span),
@@ -3439,6 +3439,15 @@ pub(crate) enum ForbiddenLetReason {
     NotSupportedParentheses(#[primary_span] Span),
 }
 
+/// Visitor to check for invalid/unstable use of `ExprKind::Let` that can't
+/// easily be caught in parsing. For example:
+///
+/// ```rust,ignore (example)
+/// // Only know that the let isn't allowed once the `||` token is reached
+/// if let Some(x) = y || true {}
+/// // Only know that the let isn't allowed once the second `=` token is reached.
+/// if let Some(x) = y && z = 1 {}
+/// ```
 struct CondChecker<'a> {
     parser: &'a Parser<'a>,
     forbid_let_reason: Option<ForbiddenLetReason>,
@@ -3495,14 +3504,14 @@ impl MutVisitor for CondChecker<'_> {
             | ExprKind::Tup(_)
             | ExprKind::Paren(_) => {
                 let forbid_let_reason = self.forbid_let_reason;
-                self.forbid_let_reason = Some(GenericForbidden);
+                self.forbid_let_reason = Some(OtherForbidden);
                 noop_visit_expr(e, self);
                 self.forbid_let_reason = forbid_let_reason;
             }
             ExprKind::Cast(ref mut op, _)
             | ExprKind::Type(ref mut op, _) => {
                 let forbid_let_reason = self.forbid_let_reason;
-                self.forbid_let_reason = Some(GenericForbidden);
+                self.forbid_let_reason = Some(OtherForbidden);
                 self.visit_expr(op);
                 self.forbid_let_reason = forbid_let_reason;
             }

tests/ui/expr/if/bad-if-let-suggestion.stderr

@@ -3,6 +3,8 @@ error: expected expression, found `let` statement
    |
 LL |     if let x = 1 && i = 2 {}
    |        ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error[E0425]: cannot find value `i` in this scope
   --> $DIR/bad-if-let-suggestion.rs:5:21

tests/ui/mir/issue-92893.stderr

@@ -3,6 +3,8 @@ error: expected expression, found `let` statement
    |
 LL | struct Bug<A = [(); (let a = (), 1).1]> {
    |                      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: aborting due to previous error
 

tests/ui/rfcs/rfc-2294-if-let-guard/feature-gate.stderr

@@ -4,6 +4,7 @@ error: expected expression, found `let` statement
 LL |         () if (let 0 = 1) => {}
    |                ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/feature-gate.rs:10:16
    |
@@ -16,6 +17,7 @@ error: expected expression, found `let` statement
 LL |         () if (((let 0 = 1))) => {}
    |                  ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/feature-gate.rs:13:18
    |
@@ -28,6 +30,7 @@ error: expected expression, found `let` statement
 LL |         () if (let 0 = 1) && true => {}
    |                ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/feature-gate.rs:24:16
    |
@@ -40,6 +43,7 @@ error: expected expression, found `let` statement
 LL |         () if true && (let 0 = 1) => {}
    |                        ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/feature-gate.rs:27:24
    |
@@ -52,6 +56,7 @@ error: expected expression, found `let` statement
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/feature-gate.rs:30:16
    |
@@ -64,6 +69,7 @@ error: expected expression, found `let` statement
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                               ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/feature-gate.rs:30:31
    |
@@ -76,6 +82,7 @@ error: expected expression, found `let` statement
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                          ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/feature-gate.rs:34:42
    |
@@ -88,6 +95,7 @@ error: expected expression, found `let` statement
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                                       ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/feature-gate.rs:34:42
    |
@@ -100,6 +108,7 @@ error: expected expression, found `let` statement
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                                                    ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/feature-gate.rs:34:42
    |
@@ -111,12 +120,16 @@ error: expected expression, found `let` statement
    |
 LL |     use_expr!((let 0 = 1 && 0 == 0));
    |                ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/feature-gate.rs:62:16
    |
 LL |     use_expr!((let 0 = 1));
    |                ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: no rules expected the token `let`
   --> $DIR/feature-gate.rs:70:15

tests/ui/rfcs/rfc-2294-if-let-guard/macro-expanded.stderr

@@ -7,6 +7,7 @@ LL |     ($e:expr) => { let Some(x) = $e }
 LL |         () if m!(Some(5)) => {}
    |               ----------- in this macro invocation
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error

tests/ui/rfcs/rfc-2294-if-let-guard/parens.stderr

@@ -4,6 +4,7 @@ error: expected expression, found `let` statement
 LL |         () if (let 0 = 1) => {}
    |                ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/parens.rs:10:16
    |
@@ -16,6 +17,7 @@ error: expected expression, found `let` statement
 LL |         () if (((let 0 = 1))) => {}
    |                  ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/parens.rs:12:18
    |
@@ -28,6 +30,7 @@ error: expected expression, found `let` statement
 LL |         () if (let 0 = 1) => {}
    |                ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/parens.rs:20:16
    |
@@ -40,6 +43,7 @@ error: expected expression, found `let` statement
 LL |         () if (((let 0 = 1))) => {}
    |                  ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/parens.rs:22:18
    |

tests/ui/rfcs/rfc-2497-if-let-chains/ast-validate-guards.stderr

@@ -4,6 +4,7 @@ error: expected expression, found `let` statement
 LL |         Ok(opt) if let Some(4) = opt || false  => {}
    |                    ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `||` operators are not supported in let chain expressions
   --> $DIR/ast-validate-guards.rs:5:38
    |

tests/ui/rfcs/rfc-2497-if-let-chains/avoid-invalid-mir.stderr

@@ -3,6 +3,8 @@ error: expected expression, found `let` statement
    |
 LL |     !let y = 42;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: aborting due to previous error
 

tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions-without-feature-gate.stderr

@@ -4,6 +4,7 @@ error: expected expression, found `let` statement
 LL |     if (let 0 = 1) {}
    |         ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:11:9
    |
@@ -16,6 +17,7 @@ error: expected expression, found `let` statement
 LL |     if (((let 0 = 1))) {}
    |           ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:14:11
    |
@@ -28,6 +30,7 @@ error: expected expression, found `let` statement
 LL |     if (let 0 = 1) && true {}
    |         ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:17:9
    |
@@ -40,6 +43,7 @@ error: expected expression, found `let` statement
 LL |     if true && (let 0 = 1) {}
    |                 ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:20:17
    |
@@ -52,6 +56,7 @@ error: expected expression, found `let` statement
 LL |     if (let 0 = 1) && (let 0 = 1) {}
    |         ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:23:9
    |
@@ -64,6 +69,7 @@ error: expected expression, found `let` statement
 LL |     if (let 0 = 1) && (let 0 = 1) {}
    |                        ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:23:24
    |
@@ -76,6 +82,7 @@ error: expected expression, found `let` statement
 LL |     if (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |         ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:27:9
    |
@@ -88,6 +95,7 @@ error: expected expression, found `let` statement
 LL |     if (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                      ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:27:9
    |
@@ -100,6 +108,7 @@ error: expected expression, found `let` statement
 LL |     if (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                   ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:27:9
    |
@@ -112,6 +121,7 @@ error: expected expression, found `let` statement
 LL |     while (let 0 = 1) {}
    |            ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:34:12
    |
@@ -124,6 +134,7 @@ error: expected expression, found `let` statement
 LL |     while (((let 0 = 1))) {}
    |              ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:37:14
    |
@@ -136,6 +147,7 @@ error: expected expression, found `let` statement
 LL |     while (let 0 = 1) && true {}
    |            ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:40:12
    |
@@ -148,6 +160,7 @@ error: expected expression, found `let` statement
 LL |     while true && (let 0 = 1) {}
    |                    ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:43:20
    |
@@ -160,6 +173,7 @@ error: expected expression, found `let` statement
 LL |     while (let 0 = 1) && (let 0 = 1) {}
    |            ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:46:12
    |
@@ -172,6 +186,7 @@ error: expected expression, found `let` statement
 LL |     while (let 0 = 1) && (let 0 = 1) {}
    |                           ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:46:27
    |
@@ -184,6 +199,7 @@ error: expected expression, found `let` statement
 LL |     while (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |            ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:50:12
    |
@@ -196,6 +212,7 @@ error: expected expression, found `let` statement
 LL |     while (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                         ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:50:12
    |
@@ -208,6 +225,7 @@ error: expected expression, found `let` statement
 LL |     while (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                      ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:50:12
    |
@@ -219,30 +237,40 @@ error: expected expression, found `let` statement
    |
 LL |     if &let 0 = 0 {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:73:9
    |
 LL |     if !let 0 = 0 {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:75:9
    |
 LL |     if *let 0 = 0 {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:77:9
    |
 LL |     if -let 0 = 0 {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:85:9
    |
 LL |     if (let 0 = 0)? {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:88:16
@@ -250,6 +278,7 @@ error: expected expression, found `let` statement
 LL |     if true || let 0 = 0 {}
    |                ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `||` operators are not supported in let chain expressions
   --> $DIR/disallowed-positions-without-feature-gate.rs:88:13
    |
@@ -261,102 +290,136 @@ error: expected expression, found `let` statement
    |
 LL |     if (true || let 0 = 0) {}
    |                 ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:92:25
    |
 LL |     if true && (true || let 0 = 0) {}
    |                         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:94:25
    |
 LL |     if true || (true && let 0 = 0) {}
    |                         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:98:12
    |
 LL |     if x = let 0 = 0 {}
    |            ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:101:15
    |
 LL |     if true..(let 0 = 0) {}
    |               ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:104:11
    |
 LL |     if ..(let 0 = 0) {}
    |           ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:106:9
    |
 LL |     if (let 0 = 0).. {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:110:8
    |
 LL |     if let Range { start: _, end: _ } = true..true && false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:113:8
    |
 LL |     if let Range { start: _, end: _ } = true..true || false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:119:8
    |
 LL |     if let Range { start: F, end } = F..|| true {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:125:8
    |
 LL |     if let Range { start: true, end } = t..&&false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:129:19
    |
 LL |     if let true = let true = true {}
    |                   ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:134:12
    |
 LL |     while &let 0 = 0 {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:137:12
    |
 LL |     while !let 0 = 0 {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:139:12
    |
 LL |     while *let 0 = 0 {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:141:12
    |
 LL |     while -let 0 = 0 {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:149:12
    |
 LL |     while (let 0 = 0)? {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:152:19
@@ -364,6 +427,7 @@ error: expected expression, found `let` statement
 LL |     while true || let 0 = 0 {}
    |                   ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `||` operators are not supported in let chain expressions
   --> $DIR/disallowed-positions-without-feature-gate.rs:152:16
    |
@@ -375,210 +439,280 @@ error: expected expression, found `let` statement
    |
 LL |     while (true || let 0 = 0) {}
    |                    ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:156:28
    |
 LL |     while true && (true || let 0 = 0) {}
    |                            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:158:28
    |
 LL |     while true || (true && let 0 = 0) {}
    |                            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:162:15
    |
 LL |     while x = let 0 = 0 {}
    |               ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:165:18
    |
 LL |     while true..(let 0 = 0) {}
    |                  ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:168:14
    |
 LL |     while ..(let 0 = 0) {}
    |              ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:170:12
    |
 LL |     while (let 0 = 0).. {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:174:11
    |
 LL |     while let Range { start: _, end: _ } = true..true && false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:177:11
    |
 LL |     while let Range { start: _, end: _ } = true..true || false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:183:11
    |
 LL |     while let Range { start: F, end } = F..|| true {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:189:11
    |
 LL |     while let Range { start: true, end } = t..&&false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:193:22
    |
 LL |     while let true = let true = true {}
    |                      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:208:6
    |
 LL |     &let 0 = 0;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:211:6
    |
 LL |     !let 0 = 0;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:213:6
    |
 LL |     *let 0 = 0;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:215:6
    |
 LL |     -let 0 = 0;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:217:13
    |
 LL |     let _ = let _ = 3;
    |             ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:225:6
    |
 LL |     (let 0 = 0)?;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:228:13
    |
 LL |     true || let 0 = 0;
    |             ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:230:14
    |
 LL |     (true || let 0 = 0);
    |              ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:232:22
    |
 LL |     true && (true || let 0 = 0);
    |                      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:236:9
    |
 LL |     x = let 0 = 0;
    |         ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:239:12
    |
 LL |     true..(let 0 = 0);
    |            ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:241:8
    |
 LL |     ..(let 0 = 0);
    |        ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:243:6
    |
 LL |     (let 0 = 0)..;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:246:6
    |
 LL |     (let Range { start: _, end: _ } = true..true || false);
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:250:6
    |
 LL |     (let true = let true = true);
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:250:17
    |
 LL |     (let true = let true = true);
    |                 ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:256:25
    |
 LL |         let x = true && let y = 1;
    |                         ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:262:19
    |
 LL |         [1, 2, 3][let _ = ()]
    |                   ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:267:6
    |
 LL |     &let 0 = 0
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:277:17
    |
 LL |         true && let 1 = 1
    |                 ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:282:17
    |
 LL |         true && let 1 = 1
    |                 ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:287:17
    |
 LL |         true && let 1 = 1
    |                 ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:298:17
    |
 LL |         true && let 1 = 1
    |                 ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expressions must be enclosed in braces to be used as const generic arguments
   --> $DIR/disallowed-positions-without-feature-gate.rs:298:9
@@ -597,6 +731,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && true) {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:307:9
    |
@@ -609,6 +744,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt) && true {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:311:9
    |
@@ -621,6 +757,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt) && (let Some(b) = a) {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:314:9
    |
@@ -633,6 +770,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt) && (let Some(b) = a) {
    |                                ^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:314:32
    |
@@ -645,6 +783,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && (let Some(b) = a)) && b == 1 {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:319:9
    |
@@ -657,6 +796,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && (let Some(b) = a)) && b == 1 {
    |                               ^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:319:31
    |
@@ -669,6 +809,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && (let Some(b) = a)) && true {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:323:9
    |
@@ -681,6 +822,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && (let Some(b) = a)) && true {
    |                               ^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:323:31
    |
@@ -693,6 +835,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && (true)) && true {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions-without-feature-gate.rs:327:9
    |
@@ -704,24 +847,32 @@ error: expected expression, found `let` statement
    |
 LL |     let x = (true && let y = 1);
    |                      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:337:20
    |
 LL |         ([1, 2, 3][let _ = ()])
    |                    ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:63:16
    |
 LL |     use_expr!((let 0 = 1 && 0 == 0));
    |                ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions-without-feature-gate.rs:65:16
    |
 LL |     use_expr!((let 0 = 1));
    |                ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error[E0308]: mismatched types
   --> $DIR/disallowed-positions-without-feature-gate.rs:101:8

tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions.stderr

@@ -4,6 +4,7 @@ error: expected expression, found `let` statement
 LL |     if (let 0 = 1) {}
    |         ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:29:9
    |
@@ -16,6 +17,7 @@ error: expected expression, found `let` statement
 LL |     if (((let 0 = 1))) {}
    |           ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:32:11
    |
@@ -28,6 +30,7 @@ error: expected expression, found `let` statement
 LL |     if (let 0 = 1) && true {}
    |         ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:35:9
    |
@@ -40,6 +43,7 @@ error: expected expression, found `let` statement
 LL |     if true && (let 0 = 1) {}
    |                 ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:38:17
    |
@@ -52,6 +56,7 @@ error: expected expression, found `let` statement
 LL |     if (let 0 = 1) && (let 0 = 1) {}
    |         ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:41:9
    |
@@ -64,6 +69,7 @@ error: expected expression, found `let` statement
 LL |     if (let 0 = 1) && (let 0 = 1) {}
    |                        ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:41:24
    |
@@ -76,6 +82,7 @@ error: expected expression, found `let` statement
 LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                   ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:45:35
    |
@@ -88,6 +95,7 @@ error: expected expression, found `let` statement
 LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                                ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:45:35
    |
@@ -100,6 +108,7 @@ error: expected expression, found `let` statement
 LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                                             ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:45:35
    |
@@ -112,6 +121,7 @@ error: expected expression, found `let` statement
 LL |     while (let 0 = 1) {}
    |            ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:52:12
    |
@@ -124,6 +134,7 @@ error: expected expression, found `let` statement
 LL |     while (((let 0 = 1))) {}
    |              ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:55:14
    |
@@ -136,6 +147,7 @@ error: expected expression, found `let` statement
 LL |     while (let 0 = 1) && true {}
    |            ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:58:12
    |
@@ -148,6 +160,7 @@ error: expected expression, found `let` statement
 LL |     while true && (let 0 = 1) {}
    |                    ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:61:20
    |
@@ -160,6 +173,7 @@ error: expected expression, found `let` statement
 LL |     while (let 0 = 1) && (let 0 = 1) {}
    |            ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:64:12
    |
@@ -172,6 +186,7 @@ error: expected expression, found `let` statement
 LL |     while (let 0 = 1) && (let 0 = 1) {}
    |                           ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:64:27
    |
@@ -184,6 +199,7 @@ error: expected expression, found `let` statement
 LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                      ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:68:38
    |
@@ -196,6 +212,7 @@ error: expected expression, found `let` statement
 LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                                   ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:68:38
    |
@@ -208,6 +225,7 @@ error: expected expression, found `let` statement
 LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                                                ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:68:38
    |
@@ -219,30 +237,40 @@ error: expected expression, found `let` statement
    |
 LL |     if &let 0 = 0 {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:91:9
    |
 LL |     if !let 0 = 0 {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:93:9
    |
 LL |     if *let 0 = 0 {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:95:9
    |
 LL |     if -let 0 = 0 {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:103:9
    |
 LL |     if (let 0 = 0)? {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:106:16
@@ -250,6 +278,7 @@ error: expected expression, found `let` statement
 LL |     if true || let 0 = 0 {}
    |                ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `||` operators are not supported in let chain expressions
   --> $DIR/disallowed-positions.rs:106:13
    |
@@ -261,102 +290,136 @@ error: expected expression, found `let` statement
    |
 LL |     if (true || let 0 = 0) {}
    |                 ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:110:25
    |
 LL |     if true && (true || let 0 = 0) {}
    |                         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:112:25
    |
 LL |     if true || (true && let 0 = 0) {}
    |                         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:116:12
    |
 LL |     if x = let 0 = 0 {}
    |            ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:119:15
    |
 LL |     if true..(let 0 = 0) {}
    |               ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:122:11
    |
 LL |     if ..(let 0 = 0) {}
    |           ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:124:9
    |
 LL |     if (let 0 = 0).. {}
    |         ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:128:8
    |
 LL |     if let Range { start: _, end: _ } = true..true && false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:131:8
    |
 LL |     if let Range { start: _, end: _ } = true..true || false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:137:8
    |
 LL |     if let Range { start: F, end } = F..|| true {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:143:8
    |
 LL |     if let Range { start: true, end } = t..&&false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:147:19
    |
 LL |     if let true = let true = true {}
    |                   ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:152:12
    |
 LL |     while &let 0 = 0 {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:155:12
    |
 LL |     while !let 0 = 0 {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:157:12
    |
 LL |     while *let 0 = 0 {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:159:12
    |
 LL |     while -let 0 = 0 {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:167:12
    |
 LL |     while (let 0 = 0)? {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:170:19
@@ -364,6 +427,7 @@ error: expected expression, found `let` statement
 LL |     while true || let 0 = 0 {}
    |                   ^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `||` operators are not supported in let chain expressions
   --> $DIR/disallowed-positions.rs:170:16
    |
@@ -375,204 +439,272 @@ error: expected expression, found `let` statement
    |
 LL |     while (true || let 0 = 0) {}
    |                    ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:174:28
    |
 LL |     while true && (true || let 0 = 0) {}
    |                            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:176:28
    |
 LL |     while true || (true && let 0 = 0) {}
    |                            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:180:15
    |
 LL |     while x = let 0 = 0 {}
    |               ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:183:18
    |
 LL |     while true..(let 0 = 0) {}
    |                  ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:186:14
    |
 LL |     while ..(let 0 = 0) {}
    |              ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:188:12
    |
 LL |     while (let 0 = 0).. {}
    |            ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:192:11
    |
 LL |     while let Range { start: _, end: _ } = true..true && false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:195:11
    |
 LL |     while let Range { start: _, end: _ } = true..true || false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:201:11
    |
 LL |     while let Range { start: F, end } = F..|| true {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:207:11
    |
 LL |     while let Range { start: true, end } = t..&&false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:211:22
    |
 LL |     while let true = let true = true {}
    |                      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:226:6
    |
 LL |     &let 0 = 0;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:229:6
    |
 LL |     !let 0 = 0;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:231:6
    |
 LL |     *let 0 = 0;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:233:6
    |
 LL |     -let 0 = 0;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:241:6
    |
 LL |     (let 0 = 0)?;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:244:13
    |
 LL |     true || let 0 = 0;
    |             ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:246:14
    |
 LL |     (true || let 0 = 0);
    |              ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:248:22
    |
 LL |     true && (true || let 0 = 0);
    |                      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:252:9
    |
 LL |     x = let 0 = 0;
    |         ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:255:12
    |
 LL |     true..(let 0 = 0);
    |            ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:257:8
    |
 LL |     ..(let 0 = 0);
    |        ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:259:6
    |
 LL |     (let 0 = 0)..;
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:262:6
    |
 LL |     (let Range { start: _, end: _ } = true..true || false);
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:266:6
    |
 LL |     (let true = let true = true);
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:266:17
    |
 LL |     (let true = let true = true);
    |                 ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:272:25
    |
 LL |         let x = true && let y = 1;
    |                         ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:278:19
    |
 LL |         [1, 2, 3][let _ = ()]
    |                   ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:283:6
    |
 LL |     &let 0 = 0
    |      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:293:17
    |
 LL |         true && let 1 = 1
    |                 ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:298:17
    |
 LL |         true && let 1 = 1
    |                 ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:303:17
    |
 LL |         true && let 1 = 1
    |                 ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:314:17
    |
 LL |         true && let 1 = 1
    |                 ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expressions must be enclosed in braces to be used as const generic arguments
   --> $DIR/disallowed-positions.rs:314:9
@@ -591,6 +723,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && true) {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:323:9
    |
@@ -603,6 +736,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt) && true {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:327:9
    |
@@ -615,6 +749,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt) && (let Some(b) = a) {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:330:9
    |
@@ -627,6 +762,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt) && (let Some(b) = a) {
    |                                ^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:330:32
    |
@@ -639,6 +775,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && (let Some(b) = a)) && b == 1 {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:337:9
    |
@@ -651,6 +788,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && (let Some(b) = a)) && b == 1 {
    |                               ^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:337:31
    |
@@ -663,6 +801,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && (let Some(b) = a)) && true {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:341:9
    |
@@ -675,6 +814,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && (let Some(b) = a)) && true {
    |                               ^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:341:31
    |
@@ -687,6 +827,7 @@ error: expected expression, found `let` statement
 LL |     if (let Some(a) = opt && (true)) && true {
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
   --> $DIR/disallowed-positions.rs:345:9
    |
@@ -698,24 +839,32 @@ error: expected expression, found `let` statement
    |
 LL |     let x = (true && let y = 1);
    |                      ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:366:20
    |
 LL |         ([1, 2, 3][let _ = ()])
    |                    ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:81:16
    |
 LL |     use_expr!((let 0 = 1 && 0 == 0));
    |                ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/disallowed-positions.rs:83:16
    |
 LL |     use_expr!((let 0 = 1));
    |                ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error[E0308]: mismatched types
   --> $DIR/disallowed-positions.rs:119:8

tests/ui/rfcs/rfc-2497-if-let-chains/ensure-that-let-else-does-not-interact-with-let-chains.stderr

@@ -14,6 +14,8 @@ error: expected expression, found `let` statement
    |
 LL |     let Some(n) = opt && let another = n else {
    |                          ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: a `&&` expression cannot be directly assigned in `let...else`
   --> $DIR/ensure-that-let-else-does-not-interact-with-let-chains.rs:15:19

tests/ui/rfcs/rfc-2497-if-let-chains/feature-gate.stderr

@@ -3,12 +3,16 @@ error: expected expression, found `let` statement
    |
 LL |     #[cfg(FALSE)] (let 0 = 1);
    |                    ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/feature-gate.rs:45:17
    |
 LL |     noop_expr!((let 0 = 1));
    |                 ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: no rules expected the token `let`
   --> $DIR/feature-gate.rs:56:15

tests/ui/rfcs/rfc-2497-if-let-chains/invalid-let-in-a-valid-let-context.stderr

@@ -3,48 +3,64 @@ error: expected expression, found `let` statement
    |
 LL |         let _ = &&let Some(x) = Some(42);
    |                   ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/invalid-let-in-a-valid-let-context.rs:13:47
    |
 LL |         if let Some(elem) = _opt && [1, 2, 3][let _ = &&let Some(x) = Some(42)] = 1 {
    |                                               ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/invalid-let-in-a-valid-let-context.rs:13:57
    |
 LL |         if let Some(elem) = _opt && [1, 2, 3][let _ = &&let Some(x) = Some(42)] = 1 {
    |                                                         ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/invalid-let-in-a-valid-let-context.rs:13:12
    |
 LL |         if let Some(elem) = _opt && [1, 2, 3][let _ = &&let Some(x) = Some(42)] = 1 {
    |            ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/invalid-let-in-a-valid-let-context.rs:24:23
    |
 LL |             [1, 2, 3][let _ = ()];
    |                       ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/invalid-let-in-a-valid-let-context.rs:33:47
    |
 LL |         if let Some(elem) = _opt && [1, 2, 3][let _ = ()] = 1 {
    |                                               ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/invalid-let-in-a-valid-let-context.rs:33:12
    |
 LL |         if let Some(elem) = _opt && [1, 2, 3][let _ = ()] = 1 {
    |            ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
   --> $DIR/invalid-let-in-a-valid-let-context.rs:42:21
    |
 LL |             let x = let y = 1;
    |                     ^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
 
 error: aborting due to 8 previous errors