Introduce hir::ExprKind::Let - Take 2

compiler/rustc_hir/src/hir.rs

@@ -1482,6 +1482,7 @@ impl Expr<'_> {
             ExprKind::Type(..) | ExprKind::Cast(..) => ExprPrecedence::Cast,
             ExprKind::DropTemps(ref expr, ..) => expr.precedence(),
             ExprKind::If(..) => ExprPrecedence::If,
+            ExprKind::Let(..) => ExprPrecedence::Let,
             ExprKind::Loop(..) => ExprPrecedence::Loop,
             ExprKind::Match(..) => ExprPrecedence::Match,
             ExprKind::Closure(..) => ExprPrecedence::Closure,
@@ -1552,6 +1553,7 @@ impl Expr<'_> {
             | ExprKind::Break(..)
             | ExprKind::Continue(..)
             | ExprKind::Ret(..)
+            | ExprKind::Let(..)
             | ExprKind::Loop(..)
             | ExprKind::Assign(..)
             | ExprKind::InlineAsm(..)
@@ -1634,6 +1636,7 @@ impl Expr<'_> {
             | ExprKind::Break(..)
             | ExprKind::Continue(..)
             | ExprKind::Ret(..)
+            | ExprKind::Let(..)
             | ExprKind::Loop(..)
             | ExprKind::Assign(..)
             | ExprKind::InlineAsm(..)
@@ -1725,6 +1728,11 @@ pub enum ExprKind<'hir> {
     /// This construct only exists to tweak the drop order in HIR lowering.
     /// An example of that is the desugaring of `for` loops.
     DropTemps(&'hir Expr<'hir>),
+    /// A `let $pat = $expr` expression.
+    ///
+    /// These are not `Local` and only occur as expressions.
+    /// The `let Some(x) = foo()` in `if let Some(x) = foo()` is an example of `Let(..)`.
+    Let(&'hir Pat<'hir>, &'hir Expr<'hir>, Span),
     /// An `if` block, with an optional else block.
     ///
     /// I.e., `if <expr> { <expr> } else { <expr> }`.
@@ -1884,15 +1892,6 @@ pub enum LocalSource {
 pub enum MatchSource {
     /// A `match _ { .. }`.
     Normal,
-    /// An `if let _ = _ { .. }` (optionally with `else { .. }`).
-    IfLetDesugar { contains_else_clause: bool },
-    /// An `if let _ = _ => { .. }` match guard.
-    IfLetGuardDesugar,
-    /// A `while _ { .. }` (which was desugared to a `loop { match _ { .. } }`).
-    WhileDesugar,
-    /// A `while let _ = _ { .. }` (which was desugared to a
-    /// `loop { match _ { .. } }`).
-    WhileLetDesugar,
     /// A desugared `for _ in _ { .. }` loop.
     ForLoopDesugar,
     /// A desugared `?` operator.
@@ -1902,12 +1901,11 @@ pub enum MatchSource {
 }
 
 impl MatchSource {
-    pub fn name(self) -> &'static str {
+    #[inline]
+    pub const fn name(self) -> &'static str {
         use MatchSource::*;
         match self {
             Normal => "match",
-            IfLetDesugar { .. } | IfLetGuardDesugar => "if",
-            WhileDesugar | WhileLetDesugar => "while",
             ForLoopDesugar => "for",
             TryDesugar => "?",
             AwaitDesugar => ".await",
@@ -1922,8 +1920,6 @@ pub enum LoopSource {
     Loop,
     /// A `while _ { .. }` loop.
     While,
-    /// A `while let _ = _ { .. }` loop.
-    WhileLet,
     /// A `for _ in _ { .. }` loop.
     ForLoop,
 }
@@ -1932,7 +1928,7 @@ impl LoopSource {
     pub fn name(self) -> &'static str {
         match self {
             LoopSource::Loop => "loop",
-            LoopSource::While | LoopSource::WhileLet => "while",
+            LoopSource::While => "while",
             LoopSource::ForLoop => "for",
         }
     }

compiler/rustc_hir/src/intravisit.rs

@@ -1163,6 +1163,10 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
         ExprKind::DropTemps(ref subexpression) => {
             visitor.visit_expr(subexpression);
         }
+        ExprKind::Let(ref pat, ref expr, _) => {
+            visitor.visit_expr(expr);
+            visitor.visit_pat(pat);
+        }
         ExprKind::If(ref cond, ref then, ref else_opt) => {
             visitor.visit_expr(cond);
             visitor.visit_expr(then);