Auto merge of #103636 - chenyukang:yukang/fix-103587-sugg-if-let, r=jackh276,davidtwco

Recover from common if let syntax mistakes/typos

Fixes #103587

2 files changed, 21 insertions, 4 deletions

diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index 0924c853715..e3acc11811f 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -421,6 +421,15 @@ pub(crate) struct ExpectedExpressionFoundLet {
 }
 
 #[derive(Diagnostic)]
+#[diag(parser_expect_eq_instead_of_eqeq)]
+pub(crate) struct ExpectedEqForLetExpr {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(applicability = "maybe-incorrect", code = "=", style = "verbose")]
+    pub sugg_span: Span,
+}
+
+#[derive(Diagnostic)]
 #[diag(parser_expected_else_block)]
 pub(crate) struct ExpectedElseBlock {
     #[primary_span]
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index d784fef2bed..da2d20e47ee 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -9,9 +9,9 @@ use crate::errors::{
     ArrayBracketsInsteadOfSpaces, ArrayBracketsInsteadOfSpacesSugg, AsyncMoveOrderIncorrect,
     BinaryFloatLiteralNotSupported, BracesForStructLiteral, CatchAfterTry, CommaAfterBaseStruct,
     ComparisonInterpretedAsGeneric, ComparisonOrShiftInterpretedAsGenericSugg,
-    DoCatchSyntaxRemoved, DotDotDot, EqFieldInit, ExpectedElseBlock, ExpectedExpressionFoundLet,
-    FieldExpressionWithGeneric, FloatLiteralRequiresIntegerPart, FoundExprWouldBeStmt,
-    HexadecimalFloatLiteralNotSupported, IfExpressionMissingCondition,
+    DoCatchSyntaxRemoved, DotDotDot, EqFieldInit, ExpectedElseBlock, ExpectedEqForLetExpr,
+    ExpectedExpressionFoundLet, FieldExpressionWithGeneric, FloatLiteralRequiresIntegerPart,
+    FoundExprWouldBeStmt, HexadecimalFloatLiteralNotSupported, IfExpressionMissingCondition,
     IfExpressionMissingThenBlock, IfExpressionMissingThenBlockSub, IntLiteralTooLarge,
     InvalidBlockMacroSegment, InvalidComparisonOperator, InvalidComparisonOperatorSub,
     InvalidFloatLiteralSuffix, InvalidFloatLiteralWidth, InvalidIntLiteralWidth,
@@ -2329,7 +2329,15 @@ impl<'a> Parser<'a> {
             RecoverColon::Yes,
             CommaRecoveryMode::LikelyTuple,
         )?;
-        self.expect(&token::Eq)?;
+        if self.token == token::EqEq {
+            self.sess.emit_err(ExpectedEqForLetExpr {
+                span: self.token.span,
+                sugg_span: self.token.span,
+            });
+            self.bump();
+        } else {
+            self.expect(&token::Eq)?;
+        }
         let expr = self.with_res(self.restrictions | Restrictions::NO_STRUCT_LITERAL, |this| {
             this.parse_assoc_expr_with(1 + prec_let_scrutinee_needs_par(), None.into())
         })?;