3 files changed, 35 insertions, 11 deletions
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 2c43563b104..f9387e29262 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1393,7 +1393,9 @@ impl<'a> Parser<'a> {
             self.parse_yield_expr(attrs)
         } else if self.is_do_yeet() {
             self.parse_yeet_expr(attrs)
-        } else if self.eat_keyword(kw::Let) {
+        } else if self.check_keyword(kw::Let) {
+            self.manage_let_chains_context();
+            self.bump();
             self.parse_let_expr(attrs)
         } else if self.eat_keyword(kw::Underscore) {
             Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore, attrs))
@@ -2355,16 +2357,30 @@ impl<'a> Parser<'a> {
         Ok(cond)
     }
 
+    // Checks if `let` is in an invalid position like `let x = let y = 1;` or
+    // if the current `let` is in a let_chains context but nested in another
+    // expression like `if let Some(_) = _opt && [1, 2, 3][let _ = ()] = 1`.
+    //
+    // This method expects that the current token is `let`.
+    fn manage_let_chains_context(&mut self) {
+        debug_assert!(matches!(self.token.kind, TokenKind::Ident(kw::Let, _)));
+        let is_in_a_let_chains_context_but_nested_in_other_expr = self.let_expr_allowed
+            && !matches!(
+                self.prev_token.kind,
+                TokenKind::AndAnd
+                    | TokenKind::CloseDelim(Delimiter::Brace)
+                    | TokenKind::Ident(kw::If, _)
+                    | TokenKind::Ident(kw::While, _)
+            );
+        if !self.let_expr_allowed || is_in_a_let_chains_context_but_nested_in_other_expr {
+            self.struct_span_err(self.token.span, "expected expression, found `let` statement")
+                .emit();
+        }
+    }
+
     /// Parses a `let $pat = $expr` pseudo-expression.
     /// The `let` token has already been eaten.
     fn parse_let_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
-        if !self.let_expr_allowed {
-            self.struct_span_err(
-                self.prev_token.span,
-                "expected expression, found `let` statement",
-            )
-            .emit();
-        }
         let lo = self.prev_token.span;
         let pat = self.parse_pat_allow_top_alt(
             None,
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index bf685aa8cad..87bc0d9762e 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -271,8 +271,7 @@ impl<'a> Parser<'a> {
             // MACRO_RULES ITEM
             self.parse_item_macro_rules(vis, has_bang)?
         } else if self.isnt_macro_invocation()
-            && (self.token.is_ident_named(Symbol::intern("import"))
-                || self.token.is_ident_named(Symbol::intern("using")))
+            && (self.token.is_ident_named(sym::import) || self.token.is_ident_named(sym::using))
         {
             return self.recover_import_as_use();
         } else if self.isnt_macro_invocation() && vis.kind.is_pub() {
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 00002f6f59b..67e6402c0ae 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -1353,7 +1353,16 @@ impl<'a> Parser<'a> {
 
     /// Parses `extern string_literal?`.
     fn parse_extern(&mut self) -> Extern {
-        if self.eat_keyword(kw::Extern) { Extern::from_abi(self.parse_abi()) } else { Extern::None }
+        if self.eat_keyword(kw::Extern) {
+            let mut extern_span = self.prev_token.span;
+            let abi = self.parse_abi();
+            if let Some(abi) = abi {
+                extern_span = extern_span.to(abi.span);
+            }
+            Extern::from_abi(abi, extern_span)
+        } else {
+            Extern::None
+        }
     }
 
     /// Parses a string literal as an ABI spec.