Auto merge of #121657 - estebank:issue-119665, r=davidtwco

Detect more cases of `=` to `:` typo

When a `Local` is fully parsed, but not followed by a `;`, keep the `:` span arround and mention it. If the type could continue being parsed as an expression, suggest replacing the `:` with a `=`.

```
error: expected one of `!`, `+`, `->`, `::`, `;`, or `=`, found `.`
 --> file.rs:2:32
  |
2 |     let _: std::env::temp_dir().join("foo");
  |          -                     ^ expected one of `!`, `+`, `->`, `::`, `;`, or `=`
  |          |
  |          while parsing the type for `_`
  |          help: use `=` if you meant to assign
```

Fix #119665.

compiler/rustc_ast/src/ast.rs

@@ -671,6 +671,16 @@ impl Pat {
         });
         contains_never_pattern
     }
+
+    /// Return a name suitable for diagnostics.
+    pub fn descr(&self) -> Option<String> {
+        match &self.kind {
+            PatKind::Wild => Some("_".to_string()),
+            PatKind::Ident(BindingAnnotation::NONE, ident, None) => Some(format!("{ident}")),
+            PatKind::Ref(pat, mutbl) => pat.descr().map(|d| format!("&{}{d}", mutbl.prefix_str())),
+            _ => None,
+        }
+    }
 }
 
 /// A single field in a struct pattern.
@@ -1053,6 +1063,7 @@ pub struct Local {
     pub ty: Option<P<Ty>>,
     pub kind: LocalKind,
     pub span: Span,
+    pub colon_sp: Option<Span>,
     pub attrs: AttrVec,
     pub tokens: Option<LazyAttrTokenStream>,
 }
@@ -3337,7 +3348,7 @@ mod size_asserts {
     static_assert_size!(Item, 136);
     static_assert_size!(ItemKind, 64);
     static_assert_size!(LitKind, 24);
-    static_assert_size!(Local, 72);
+    static_assert_size!(Local, 80);
     static_assert_size!(MetaItemLit, 40);
     static_assert_size!(Param, 40);
     static_assert_size!(Pat, 72);

compiler/rustc_ast/src/mut_visit.rs

@@ -609,7 +609,7 @@ pub fn noop_visit_parenthesized_parameter_data<T: MutVisitor>(
 }
 
 pub fn noop_visit_local<T: MutVisitor>(local: &mut P<Local>, vis: &mut T) {
-    let Local { id, pat, ty, kind, span, attrs, tokens } = local.deref_mut();
+    let Local { id, pat, ty, kind, span, colon_sp, attrs, tokens } = local.deref_mut();
     vis.visit_id(id);
     vis.visit_pat(pat);
     visit_opt(ty, |ty| vis.visit_ty(ty));
@@ -624,6 +624,7 @@ pub fn noop_visit_local<T: MutVisitor>(local: &mut P<Local>, vis: &mut T) {
         }
     }
     vis.visit_span(span);
+    visit_opt(colon_sp, |sp| vis.visit_span(sp));
     visit_attrs(attrs, vis);
     visit_lazy_tts(tokens, vis);
 }

compiler/rustc_expand/src/build.rs

@@ -165,6 +165,7 @@ impl<'a> ExtCtxt<'a> {
             id: ast::DUMMY_NODE_ID,
             kind: LocalKind::Init(ex),
             span: sp,
+            colon_sp: None,
             attrs: AttrVec::new(),
             tokens: None,
         });
@@ -194,6 +195,7 @@ impl<'a> ExtCtxt<'a> {
             id: ast::DUMMY_NODE_ID,
             kind: LocalKind::Init(ex),
             span: sp,
+            colon_sp: None,
             attrs: AttrVec::new(),
             tokens: None,
         });
@@ -208,6 +210,7 @@ impl<'a> ExtCtxt<'a> {
             id: ast::DUMMY_NODE_ID,
             kind: LocalKind::Decl,
             span,
+            colon_sp: None,
             attrs: AttrVec::new(),
             tokens: None,
         });

compiler/rustc_parse/src/parser/expr.rs

@@ -430,7 +430,7 @@ impl<'a> Parser<'a> {
     /// The method does not advance the current token.
     ///
     /// Also performs recovery for `and` / `or` which are mistaken for `&&` and `||` respectively.
-    fn check_assoc_op(&self) -> Option<Spanned<AssocOp>> {
+    pub fn check_assoc_op(&self) -> Option<Spanned<AssocOp>> {
         let (op, span) = match (AssocOp::from_token(&self.token), self.token.ident()) {
             // When parsing const expressions, stop parsing when encountering `>`.
             (
@@ -994,7 +994,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
+    pub fn parse_dot_suffix_expr(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
         match self.token.uninterpolate().kind {
             token::Ident(..) => self.parse_dot_suffix(base, lo),
             token::Literal(token::Lit { kind: token::Integer, symbol, suffix }) => {

compiler/rustc_parse/src/parser/stmt.rs

@@ -294,17 +294,22 @@ impl<'a> Parser<'a> {
         let (pat, colon) =
             self.parse_pat_before_ty(None, RecoverComma::Yes, PatternLocation::LetBinding)?;
 
-        let (err, ty) = if colon {
+        let (err, ty, colon_sp) = if colon {
             // Save the state of the parser before parsing type normally, in case there is a `:`
             // instead of an `=` typo.
             let parser_snapshot_before_type = self.clone();
             let colon_sp = self.prev_token.span;
             match self.parse_ty() {
-                Ok(ty) => (None, Some(ty)),
+                Ok(ty) => (None, Some(ty), Some(colon_sp)),
                 Err(mut err) => {
-                    if let Ok(snip) = self.span_to_snippet(pat.span) {
-                        err.span_label(pat.span, format!("while parsing the type for `{snip}`"));
-                    }
+                    err.span_label(
+                        colon_sp,
+                        format!(
+                            "while parsing the type for {}",
+                            pat.descr()
+                                .map_or_else(|| "the binding".to_string(), |n| format!("`{n}`"))
+                        ),
+                    );
                     // we use noexpect here because we don't actually expect Eq to be here
                     // but we are still checking for it in order to be able to handle it if
                     // it is there
@@ -317,11 +322,11 @@ impl<'a> Parser<'a> {
                             mem::replace(self, parser_snapshot_before_type);
                         Some((parser_snapshot_after_type, colon_sp, err))
                     };
-                    (err, None)
+                    (err, None, Some(colon_sp))
                 }
             }
         } else {
-            (None, None)
+            (None, None, None)
         };
         let init = match (self.parse_initializer(err.is_some()), err) {
             (Ok(init), None) => {
@@ -380,7 +385,16 @@ impl<'a> Parser<'a> {
             }
         };
         let hi = if self.token == token::Semi { self.token.span } else { self.prev_token.span };
-        Ok(P(ast::Local { ty, pat, kind, id: DUMMY_NODE_ID, span: lo.to(hi), attrs, tokens: None }))
+        Ok(P(ast::Local {
+            ty,
+            pat,
+            kind,
+            id: DUMMY_NODE_ID,
+            span: lo.to(hi),
+            colon_sp,
+            attrs,
+            tokens: None,
+        }))
     }
 
     fn check_let_else_init_bool_expr(&self, init: &ast::Expr) {
@@ -750,15 +764,55 @@ impl<'a> Parser<'a> {
                 }
             }
             StmtKind::Expr(_) | StmtKind::MacCall(_) => {}
-            StmtKind::Local(local) if let Err(e) = self.expect_semi() => {
+            StmtKind::Local(local) if let Err(mut e) = self.expect_semi() => {
                 // We might be at the `,` in `let x = foo<bar, baz>;`. Try to recover.
                 match &mut local.kind {
                     LocalKind::Init(expr) | LocalKind::InitElse(expr, _) => {
                         self.check_mistyped_turbofish_with_multiple_type_params(e, expr)?;
                         // We found `foo<bar, baz>`, have we fully recovered?
                         self.expect_semi()?;
                     }
-                    LocalKind::Decl => return Err(e),
+                    LocalKind::Decl => {
+                        if let Some(colon_sp) = local.colon_sp {
+                            e.span_label(
+                                colon_sp,
+                                format!(
+                                    "while parsing the type for {}",
+                                    local.pat.descr().map_or_else(
+                                        || "the binding".to_string(),
+                                        |n| format!("`{n}`")
+                                    )
+                                ),
+                            );
+                            let suggest_eq = if self.token.kind == token::Dot
+                                && let _ = self.bump()
+                                && let mut snapshot = self.create_snapshot_for_diagnostic()
+                                && let Ok(_) = snapshot.parse_dot_suffix_expr(
+                                    colon_sp,
+                                    self.mk_expr_err(
+                                        colon_sp,
+                                        self.dcx().delayed_bug("error during `:` -> `=` recovery"),
+                                    ),
+                                ) {
+                                true
+                            } else if let Some(op) = self.check_assoc_op()
+                                && op.node.can_continue_expr_unambiguously()
+                            {
+                                true
+                            } else {
+                                false
+                            };
+                            if suggest_eq {
+                                e.span_suggestion_short(
+                                    colon_sp,
+                                    "use `=` if you meant to assign",
+                                    "=",
+                                    Applicability::MaybeIncorrect,
+                                );
+                            }
+                        }
+                        return Err(e);
+                    }
                 }
                 eat_semi = false;
             }

tests/ui/const-generics/bad-const-generic-exprs.stderr

@@ -146,9 +146,9 @@ error: expected one of `,` or `>`, found `0`
   --> $DIR/bad-const-generic-exprs.rs:43:17
    |
 LL |     let _: Wow<!0>;
-   |         -       ^ expected one of `,` or `>`
-   |         |
-   |         while parsing the type for `_`
+   |          -      ^ expected one of `,` or `>`
+   |          |
+   |          while parsing the type for `_`
    |
 help: you might have meant to end the type parameters here
    |

tests/ui/issues/issue-34334.stderr

@@ -2,9 +2,9 @@ error: expected one of `,`, `:`, or `>`, found `=`
   --> $DIR/issue-34334.rs:2:29
    |
 LL |     let sr: Vec<(u32, _, _) = vec![];
-   |         --                  ^ expected one of `,`, `:`, or `>`
-   |         |
-   |         while parsing the type for `sr`
+   |           -                 ^ expected one of `,`, `:`, or `>`
+   |           |
+   |           while parsing the type for `sr`
    |
 help: you might have meant to end the type parameters here
    |

tests/ui/parser/better-expected.stderr

@@ -2,9 +2,9 @@ error: expected one of `!`, `(`, `+`, `::`, `;`, `<`, or `]`, found `3`
   --> $DIR/better-expected.rs:2:19
    |
 LL |     let x: [isize 3];
-   |         -         ^ expected one of 7 possible tokens
-   |         |
-   |         while parsing the type for `x`
+   |          -        ^ expected one of 7 possible tokens
+   |          |
+   |          while parsing the type for `x`
 
 error: aborting due to 1 previous error
 

tests/ui/parser/issues/issue-84117.stderr

@@ -2,9 +2,9 @@ error: expected one of `>`, a const expression, lifetime, or type, found `}`
   --> $DIR/issue-84117.rs:2:67
    |
 LL |     let outer_local:e_outer<&str, { let inner_local:e_inner<&str, }
-   |                                         -----------               ^ expected one of `>`, a const expression, lifetime, or type
-   |                                         |
-   |                                         while parsing the type for `inner_local`
+   |                                                    -              ^ expected one of `>`, a const expression, lifetime, or type
+   |                                                    |
+   |                                                    while parsing the type for `inner_local`
    |
 help: you might have meant to end the type parameters here
    |
@@ -25,7 +25,7 @@ error: expected one of `,` or `>`, found `}`
   --> $DIR/issue-84117.rs:8:1
    |
 LL |     let outer_local:e_outer<&str, { let inner_local:e_inner<&str, }
-   |         ----------- while parsing the type for `outer_local`       - expected one of `,` or `>`
+   |                    - while parsing the type for `outer_local`      - expected one of `,` or `>`
 ...
 LL | }
    | ^ unexpected token
@@ -43,9 +43,9 @@ error: expected one of `>`, a const expression, lifetime, or type, found `}`
   --> $DIR/issue-84117.rs:2:67
    |
 LL |     let outer_local:e_outer<&str, { let inner_local:e_inner<&str, }
-   |                                         -----------               ^ expected one of `>`, a const expression, lifetime, or type
-   |                                         |
-   |                                         while parsing the type for `inner_local`
+   |                                                    -              ^ expected one of `>`, a const expression, lifetime, or type
+   |                                                    |
+   |                                                    while parsing the type for `inner_local`
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 help: you might have meant to end the type parameters here

tests/ui/parser/missing-closing-angle-bracket-eq-constraint.stderr

@@ -2,9 +2,9 @@ error: expected one of `,`, `:`, or `>`, found `=`
   --> $DIR/missing-closing-angle-bracket-eq-constraint.rs:7:23
    |
 LL |   let v : Vec<(u32,_) = vec![];
-   |       -               ^ expected one of `,`, `:`, or `>`
-   |       |
-   |       while parsing the type for `v`
+   |         -             ^ expected one of `,`, `:`, or `>`
+   |         |
+   |         while parsing the type for `v`
    |
 help: you might have meant to end the type parameters here
    |
@@ -15,9 +15,9 @@ error: expected one of `!`, `(`, `+`, `,`, `::`, `<`, or `>`, found `{`
   --> $DIR/missing-closing-angle-bracket-eq-constraint.rs:13:32
    |
 LL |   let foo : Foo::<T1, T2 = Foo {_a : arg1, _b : arg2};
-   |       ---                      ^ expected one of 7 possible tokens
-   |       |
-   |       while parsing the type for `foo`
+   |           -                    ^ expected one of 7 possible tokens
+   |           |
+   |           while parsing the type for `foo`
    |
 help: you might have meant to end the type parameters here
    |
@@ -28,9 +28,9 @@ error: expected one of `,`, `:`, or `>`, found `=`
   --> $DIR/missing-closing-angle-bracket-eq-constraint.rs:18:18
    |
 LL |   let v : Vec<'a = vec![];
-   |       -          ^ expected one of `,`, `:`, or `>`
-   |       |
-   |       while parsing the type for `v`
+   |         -        ^ expected one of `,`, `:`, or `>`
+   |         |
+   |         while parsing the type for `v`
    |
 help: you might have meant to end the type parameters here
    |

tests/ui/parser/nested-missing-closing-angle-bracket.stderr

@@ -2,7 +2,7 @@ error: expected one of `,` or `>`, found `;`
   --> $DIR/nested-missing-closing-angle-bracket.rs:2:46
    |
 LL |   let v : Vec::<Vec<(u32,_,_)> = vec![vec![]];
-   |       - while parsing the type for `v`       ^ expected one of `,` or `>`
+   |         - while parsing the type for `v`     ^ expected one of `,` or `>`
 
 error: aborting due to 1 previous error
 

tests/ui/parser/recover/recover-colon-instead-of-eq-in-local.rs

@@ -0,0 +1,3 @@
+fn main() {
+    let _: std::env::temp_dir().join("foo"); //~ ERROR expected one of
+}

tests/ui/parser/recover/recover-colon-instead-of-eq-in-local.stderr

@@ -0,0 +1,11 @@
+error: expected one of `!`, `+`, `->`, `::`, `;`, or `=`, found `.`
+  --> $DIR/recover-colon-instead-of-eq-in-local.rs:2:32
+   |
+LL |     let _: std::env::temp_dir().join("foo");
+   |          -                     ^ expected one of `!`, `+`, `->`, `::`, `;`, or `=`
+   |          |
+   |          while parsing the type for `_`
+   |          help: use `=` if you meant to assign
+
+error: aborting due to 1 previous error
+

tests/ui/parser/removed-syntax/removed-syntax-fn-sigil.stderr

@@ -8,7 +8,9 @@ error: expected one of `->`, `;`, or `=`, found `~`
   --> $DIR/removed-syntax-fn-sigil.rs:2:14
    |
 LL |     let x: fn~() = || ();
-   |              ^ expected one of `->`, `;`, or `=`
+   |          -   ^ expected one of `->`, `;`, or `=`
+   |          |
+   |          while parsing the type for `x`
 
 error: aborting due to 2 previous errors
 

tests/ui/pattern/bindings-after-at/nested-type-ascription-syntactically-invalid.stderr

@@ -2,7 +2,9 @@ error: expected one of `!`, `(`, `+`, `::`, `;`, `<`, or `=`, found `@`
   --> $DIR/nested-type-ascription-syntactically-invalid.rs:18:15
    |
 LL |     let a: u8 @ b = 0;
-   |               ^ expected one of 7 possible tokens
+   |          -    ^ expected one of 7 possible tokens
+   |          |
+   |          while parsing the type for `a`
 
 error: expected one of `)`, `,`, `@`, or `|`, found `:`
   --> $DIR/nested-type-ascription-syntactically-invalid.rs:24:15
@@ -16,7 +18,9 @@ error: expected one of `!`, `(`, `+`, `::`, `;`, `<`, or `=`, found `@`
   --> $DIR/nested-type-ascription-syntactically-invalid.rs:30:15
    |
 LL |     let a: T1 @ Outer(b: T2);
-   |               ^ expected one of 7 possible tokens
+   |          -    ^ expected one of 7 possible tokens
+   |          |
+   |          while parsing the type for `a`
 
 error: aborting due to 3 previous errors