Brace-ident-colon can certainly no longer start a block

thanks to the removal of type ascription.

compiler/rustc_parse/src/parser/expr.rs

@@ -3474,19 +3474,9 @@ impl<'a> Parser<'a> {
     }
 
     fn is_certainly_not_a_block(&self) -> bool {
+        // `{ ident, ` and `{ ident: ` cannot start a block.
         self.look_ahead(1, |t| t.is_ident())
-            && (
+            && self.look_ahead(2, |t| t == &token::Comma || t == &token::Colon)
-                // `{ ident, ` cannot start a block.
-                self.look_ahead(2, |t| t == &token::Comma)
-                    || self.look_ahead(2, |t| t == &token::Colon)
-                        && (
-                            // `{ ident: token, ` cannot start a block.
-                            self.look_ahead(4, |t| t == &token::Comma)
-                                // `{ ident: ` cannot start a block unless it's a type ascription
-                                // `ident: Type`.
-                                || self.look_ahead(3, |t| !t.can_begin_type())
-                        )
-            )
     }
 
     fn maybe_parse_struct_expr(

tests/ui/parser/issues/issue-111692.rs

@@ -9,23 +9,25 @@ mod module {
 }
 
 fn test(x: module::Type) {
-    if x == module::Type { x: module::C, y: 1 } { //~ ERROR invalid struct literal
+    if x == module::Type { x: module::C, y: 1 } { //~ ERROR struct literals are not allowed here
     }
 }
 
 fn test2(x: module::Type) {
-    if x ==module::Type { x: module::C, y: 1 } { //~ ERROR invalid struct literal
+    if x ==module::Type { x: module::C, y: 1 } { //~ ERROR struct literals are not allowed here
     }
 }
 
 
 fn test3(x: module::Type) {
-    if x == Type { x: module::C, y: 1 } { //~ ERROR invalid struct literal
+    use module::Type;
+    if x == Type { x: module::C, y: 1 } { //~ ERROR struct literals are not allowed here
     }
 }
 
 fn test4(x: module::Type) {
-    if x == demo_module::Type { x: module::C, y: 1 } { //~ ERROR invalid struct literal
+    use module as demo_module;
+    if x == demo_module::Type { x: module::C, y: 1 } { //~ ERROR struct literals are not allowed here
     }
 }
 

tests/ui/parser/issues/issue-111692.stderr

@@ -1,43 +1,43 @@
-error: invalid struct literal
+error: struct literals are not allowed here
-  --> $DIR/issue-111692.rs:12:21
+  --> $DIR/issue-111692.rs:12:13
    |
 LL |     if x == module::Type { x: module::C, y: 1 } {
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-help: you might need to surround the struct literal with parentheses
+help: surround the struct literal with parentheses
    |
 LL |     if x == (module::Type { x: module::C, y: 1 }) {
    |             +                                   +
 
-error: invalid struct literal
+error: struct literals are not allowed here
-  --> $DIR/issue-111692.rs:17:20
+  --> $DIR/issue-111692.rs:17:12
    |
 LL |     if x ==module::Type { x: module::C, y: 1 } {
-   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-help: you might need to surround the struct literal with parentheses
+help: surround the struct literal with parentheses
    |
 LL |     if x ==(module::Type { x: module::C, y: 1 }) {
    |            +                                   +
 
-error: invalid struct literal
+error: struct literals are not allowed here
-  --> $DIR/issue-111692.rs:23:13
+  --> $DIR/issue-111692.rs:24:13
    |
 LL |     if x == Type { x: module::C, y: 1 } {
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-help: you might need to surround the struct literal with parentheses
+help: surround the struct literal with parentheses
    |
 LL |     if x == (Type { x: module::C, y: 1 }) {
    |             +                           +
 
-error: invalid struct literal
+error: struct literals are not allowed here
-  --> $DIR/issue-111692.rs:28:26
+  --> $DIR/issue-111692.rs:30:13
    |
 LL |     if x == demo_module::Type { x: module::C, y: 1 } {
-   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-help: you might need to surround the struct literal with parentheses
+help: surround the struct literal with parentheses
    |
 LL |     if x == (demo_module::Type { x: module::C, y: 1 }) {
    |             +                                        +

tests/ui/parser/method-call-on-struct-literal-in-if-condition.rs

@@ -7,7 +7,7 @@ impl Example {
 fn one() -> i32 { 1 }
 
 fn main() {
-    if Example { a: one(), }.is_pos() { //~ ERROR invalid struct literal
+    if Example { a: one(), }.is_pos() { //~ ERROR struct literals are not allowed here
         println!("Positive!");
     }
 }

tests/ui/parser/method-call-on-struct-literal-in-if-condition.stderr

@@ -1,10 +1,10 @@
-error: invalid struct literal
+error: struct literals are not allowed here
   --> $DIR/method-call-on-struct-literal-in-if-condition.rs:10:8
    |
 LL |     if Example { a: one(), }.is_pos() {
    |        ^^^^^^^^^^^^^^^^^^^^^
    |
-help: you might need to surround the struct literal with parentheses
+help: surround the struct literal with parentheses
    |
 LL |     if (Example { a: one(), }).is_pos() {
    |        +                     +

tests/ui/parser/type-ascription-in-pattern.rs

@@ -1,11 +1,10 @@
 fn foo(x: bool) -> i32 {
-    match x {
+    match x { //~ ERROR struct literals are not allowed here
         x: i32 => x, //~ ERROR expected
-        //~^ ERROR mismatched types
+        true => 42., //~ ERROR expected identifier
-        true => 42.,
+        false => 0.333, //~ ERROR expected identifier
-        false => 0.333,
-    }
     }
+} //~ ERROR expected one of
 
 fn main() {
     match foo(true) {

tests/ui/parser/type-ascription-in-pattern.stderr

@@ -1,18 +1,64 @@
-error: expected one of `@` or `|`, found `:`
+error: expected one of `!`, `,`, `.`, `::`, `?`, `{`, `}`, or an operator, found `=>`
-  --> $DIR/type-ascription-in-pattern.rs:3:10
+  --> $DIR/type-ascription-in-pattern.rs:3:16
    |
+LL |     match x {
+   |           - while parsing this struct
 LL |         x: i32 => x,
-   |          ^ --- specifying the type of a pattern isn't supported
+   |               -^^ expected one of 8 possible tokens
    |               |
-   |          expected one of `@` or `|`
+   |               help: try adding a comma: `,`
+
+error: expected identifier, found keyword `true`
+  --> $DIR/type-ascription-in-pattern.rs:4:9
    |
-help: maybe write a path separator here
+LL |     match x {
+   |           - while parsing this struct
+LL |         x: i32 => x,
+LL |         true => 42.,
+   |         ^^^^ expected identifier, found keyword
+
+error: expected identifier, found keyword `false`
+  --> $DIR/type-ascription-in-pattern.rs:5:9
    |
-LL |         x::i32 => x,
+LL |     match x {
-   |          ~~
+   |           - while parsing this struct
+...
+LL |         false => 0.333,
+   |         ^^^^^ expected identifier, found keyword
+
+error: struct literals are not allowed here
+  --> $DIR/type-ascription-in-pattern.rs:2:11
+   |
+LL |       match x {
+   |  ___________^
+LL | |         x: i32 => x,
+LL | |         true => 42.,
+LL | |         false => 0.333,
+LL | |     }
+   | |_____^
+   |
+help: surround the struct literal with parentheses
+   |
+LL ~     match (x {
+LL |         x: i32 => x,
+LL |         true => 42.,
+LL |         false => 0.333,
+LL ~     })
+   |
+
+error: expected one of `.`, `?`, `{`, or an operator, found `}`
+  --> $DIR/type-ascription-in-pattern.rs:7:1
+   |
+LL |     match x {
+   |     ----- while parsing this `match` expression
+...
+LL |     }
+   |      - expected one of `.`, `?`, `{`, or an operator
+LL | }
+   | ^ unexpected token
 
 error: expected one of `...`, `..=`, `..`, or `|`, found `:`
-  --> $DIR/type-ascription-in-pattern.rs:12:11
+  --> $DIR/type-ascription-in-pattern.rs:11:11
    |
 LL |         42: i32 => (),
    |           ^ --- specifying the type of a pattern isn't supported
@@ -20,7 +66,7 @@ LL |         42: i32 => (),
    |           expected one of `...`, `..=`, `..`, or `|`
 
 error: expected `|`, found `:`
-  --> $DIR/type-ascription-in-pattern.rs:13:10
+  --> $DIR/type-ascription-in-pattern.rs:12:10
    |
 LL |         _: f64 => (),
    |          ^ --- specifying the type of a pattern isn't supported
@@ -28,7 +74,7 @@ LL |         _: f64 => (),
    |          expected `|`
 
 error: expected one of `@` or `|`, found `:`
-  --> $DIR/type-ascription-in-pattern.rs:14:10
+  --> $DIR/type-ascription-in-pattern.rs:13:10
    |
 LL |         x: i32 => (),
    |          ^ --- specifying the type of a pattern isn't supported
@@ -40,15 +86,5 @@ help: maybe write a path separator here
 LL |         x::i32 => (),
    |          ~~
 
-error[E0308]: mismatched types
+error: aborting due to 8 previous errors
-  --> $DIR/type-ascription-in-pattern.rs:3:19
-   |
-LL | fn foo(x: bool) -> i32 {
-   |                    --- expected `i32` because of return type
-LL |     match x {
-LL |         x: i32 => x,
-   |                   ^ expected `i32`, found `bool`
 
-error: aborting due to 5 previous errors
-
-For more information about this error, try `rustc --explain E0308`.