Improve diagnostics when parsing angle args

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -2,14 +2,13 @@ use super::ty::AllowPlus;
 use super::TokenType;
 use super::{BlockMode, Parser, PathStyle, Restrictions, SemiColonMode, SeqSep, TokenExpectType};
 
+use rustc_ast as ast;
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Lit, LitKind, TokenKind};
 use rustc_ast::util::parser::AssocOp;
-use rustc_ast::{
-    self as ast, AngleBracketedArg, AngleBracketedArgs, AnonConst, AttrVec, BinOpKind, BindingMode,
-    Block, BlockCheckMode, Expr, ExprKind, GenericArg, Item, ItemKind, Mutability, Param, Pat,
-    PatKind, Path, PathSegment, QSelf, Ty, TyKind,
-};
+use rustc_ast::{AngleBracketedArg, AngleBracketedArgs, AnonConst, AttrVec};
+use rustc_ast::{BinOpKind, BindingMode, Block, BlockCheckMode, Expr, ExprKind, GenericArg, Item};
+use rustc_ast::{ItemKind, Mutability, Param, Pat, PatKind, Path, PathSegment, QSelf, Ty, TyKind};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{pluralize, struct_span_err};
@@ -220,6 +219,7 @@ impl<'a> Parser<'a> {
         edible: &[TokenKind],
         inedible: &[TokenKind],
     ) -> PResult<'a, bool /* recovered */> {
+        debug!("expected_one_of_not_found(edible: {:?}, inedible: {:?})", edible, inedible);
         fn tokens_to_string(tokens: &[TokenType]) -> String {
             let mut i = tokens.iter();
             // This might be a sign we need a connect method on `Iterator`.
@@ -245,6 +245,7 @@ impl<'a> Parser<'a> {
             .collect::<Vec<_>>();
         expected.sort_by_cached_key(|x| x.to_string());
         expected.dedup();
+
         let expect = tokens_to_string(&expected[..]);
         let actual = super::token_descr(&self.token);
         let (msg_exp, (label_sp, label_exp)) = if expected.len() > 1 {
@@ -270,6 +271,16 @@ impl<'a> Parser<'a> {
         };
         self.last_unexpected_token_span = Some(self.token.span);
         let mut err = self.struct_span_err(self.token.span, &msg_exp);
+
+        // Add suggestion for a missing closing angle bracket if '>' is included in expected_tokens
+        // there are unclosed angle brackets
+        if self.unmatched_angle_bracket_count > 0
+            && self.token.kind == TokenKind::Eq
+            && expected.iter().any(|tok| matches!(tok, TokenType::Token(TokenKind::Gt)))
+        {
+            err.span_label(self.prev_token.span, "maybe try to close unmatched angle bracket");
+        }
+
         let sp = if self.token == token::Eof {
             // This is EOF; don't want to point at the following char, but rather the last token.
             self.prev_token.span

compiler/rustc_parse/src/parser/mod.rs

@@ -272,7 +272,7 @@ impl TokenCursor {
     }
 }
 
-#[derive(Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq)]
 enum TokenType {
     Token(TokenKind),
     Keyword(Symbol),

compiler/rustc_parse/src/parser/path.rs

@@ -185,7 +185,6 @@ impl<'a> Parser<'a> {
 
     pub(super) fn parse_path_segment(&mut self, style: PathStyle) -> PResult<'a, PathSegment> {
         let ident = self.parse_path_segment_ident()?;
-
         let is_args_start = |token: &Token| {
             matches!(
                 token.kind,
@@ -420,7 +419,10 @@ impl<'a> Parser<'a> {
         match arg {
             Some(arg) => {
                 if self.check(&token::Colon) | self.check(&token::Eq) {
-                    let (ident, gen_args) = self.get_ident_from_generic_arg(arg, lo)?;
+                    let (ident, gen_args) = match self.get_ident_from_generic_arg(arg) {
+                        Ok(ident_gen_args) => ident_gen_args,
+                        Err(arg) => return Ok(Some(AngleBracketedArg::Arg(arg))),
+                    };
                     let kind = if self.eat(&token::Colon) {
                         // Parse associated type constraint bound.
 
@@ -561,50 +563,15 @@ impl<'a> Parser<'a> {
     fn get_ident_from_generic_arg(
         &self,
         gen_arg: GenericArg,
-        lo: Span,
-    ) -> PResult<'a, (Ident, Option<GenericArgs>)> {
-        let gen_arg_span = gen_arg.span();
-        match gen_arg {
-            GenericArg::Type(t) => match t.into_inner().kind {
-                ast::TyKind::Path(qself, mut path) => {
-                    if let Some(qself) = qself {
-                        let mut err = self.struct_span_err(
-                            gen_arg_span,
-                            "qualified paths cannot be used in associated type constraints",
-                        );
-                        err.span_label(
-                            qself.path_span,
-                            "not allowed in associated type constraints",
-                        );
-                        return Err(err);
-                    }
-                    if path.segments.len() == 1 {
-                        let path_seg = path.segments.remove(0);
-                        let ident = path_seg.ident;
-                        let gen_args = path_seg.args.map(|args| args.into_inner());
-                        return Ok((ident, gen_args));
-                    }
-                    let err = self.struct_span_err(
-                        path.span,
-                        "paths with multiple segments cannot be used in associated type constraints",
-                    );
-                    return Err(err);
-                }
-                _ => {
-                    let span = lo.to(self.prev_token.span);
-                    let err = self.struct_span_err(
-                        span,
-                        "only path types can be used in associated type constraints",
-                    );
-                    return Err(err);
+    ) -> Result<(Ident, Option<GenericArgs>), GenericArg> {
+        if let GenericArg::Type(ty) = &gen_arg {
+            if let ast::TyKind::Path(qself, path) = &ty.kind {
+                if qself.is_none() && path.segments.len() == 1 {
+                    let seg = &path.segments[0];
+                    return Ok((seg.ident, seg.args.as_deref().cloned()));
                 }
-            },
-            _ => {
-                let span = lo.to(self.prev_token.span);
-                let err = self
-                    .struct_span_err(span, "only types can be used in associated type constraints");
-                return Err(err);
             }
         }
+        Err(gen_arg)
     }
 }

src/test/ui/generic-associated-types/parse/trait-path-expected-token.stderr

@@ -2,7 +2,9 @@ error: expected one of `!`, `(`, `+`, `,`, `::`, `<`, or `>`, found `=`
   --> $DIR/trait-path-expected-token.rs:8:33
    |
 LL | fn f1<'a>(arg : Box<dyn X<Y = B = &'a ()>>) {}
-   |                                 ^ expected one of 7 possible tokens
+   |                               - ^ expected one of 7 possible tokens
+   |                               |
+   |                               maybe try to close unmatched angle bracket
 
 warning: the feature `generic_associated_types` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/trait-path-expected-token.rs:1:12

src/test/ui/generic-associated-types/parse/trait-path-expressions.rs

@@ -17,7 +17,7 @@ mod error2 {
   }
 
   fn f2<'a>(arg : Box<dyn X< { 1 } = 32 >>) {}
-    //~^ ERROR: only types can be used in associated type constraints
+    //~^ ERROR: expected one of
 }
 
 fn main() {}

src/test/ui/generic-associated-types/parse/trait-path-expressions.stderr

@@ -6,11 +6,13 @@ LL |   fn f1<'a>(arg : Box<dyn X< 1 = 32 >>) {}
    |                              |
    |                              while parsing a const generic argument starting here
 
-error: only types can be used in associated type constraints
-  --> $DIR/trait-path-expressions.rs:19:30
+error: expected one of `,`, `:`, or `>`, found `=`
+  --> $DIR/trait-path-expressions.rs:19:36
    |
 LL |   fn f2<'a>(arg : Box<dyn X< { 1 } = 32 >>) {}
-   |                              ^^^^^
+   |                                  - ^ expected one of `,`, `:`, or `>`
+   |                                  |
+   |                                  maybe try to close unmatched angle bracket
 
 warning: the feature `generic_associated_types` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/trait-path-expressions.rs:1:12

src/test/ui/generic-associated-types/parse/trait-path-missing-gen_arg.stderr

@@ -28,7 +28,9 @@ error: expected one of `>`, a const expression, lifetime, or type, found `=`
   --> $DIR/trait-path-missing-gen_arg.rs:17:30
    |
 LL |   fn f1<'a>(arg : Box<dyn X< = 32 >>) {}
-   |                              ^ expected one of `>`, a const expression, lifetime, or type
+   |                            - ^ expected one of `>`, a const expression, lifetime, or type
+   |                            |
+   |                            maybe try to close unmatched angle bracket
 
 warning: the feature `generic_associated_types` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/trait-path-missing-gen_arg.rs:1:12

src/test/ui/generic-associated-types/parse/trait-path-segments.rs

@@ -7,7 +7,7 @@ const _: () = {
     }
 
     fn f1<'a>(arg : Box<dyn X<X::Y = u32>>) {}
-        //~^ ERROR: paths with multiple segments cannot be used in associated type constraints
+        //~^ ERROR: expected one of
   };
 
 const _: () = {
@@ -18,7 +18,7 @@ const _: () = {
     trait Z {}
 
     impl<T : X<<Self as X>::Y<'a> = &'a u32>> Z for T {}
-        //~^ ERROR: qualified paths cannot be used in associated type constraints
+        //~^ ERROR: expected one of
 };
 
 const _: () = {
@@ -29,7 +29,7 @@ const _: () = {
     trait Z {}
 
     impl<T : X<X::Y<'a> = &'a u32>> Z for T {}
-        //~^ ERROR: paths with multiple segments cannot be used in associated type constraints
+        //~^ ERROR: expected one of
 };
 
 fn main() {}

src/test/ui/generic-associated-types/parse/trait-path-segments.stderr

@@ -1,22 +1,26 @@
-error: paths with multiple segments cannot be used in associated type constraints
-  --> $DIR/trait-path-segments.rs:9:31
+error: expected one of `!`, `(`, `+`, `,`, `::`, `:`, `<`, or `>`, found `=`
+  --> $DIR/trait-path-segments.rs:9:36
    |
 LL |     fn f1<'a>(arg : Box<dyn X<X::Y = u32>>) {}
-   |                               ^^^^
+   |                                  - ^ expected one of 8 possible tokens
+   |                                  |
+   |                                  maybe try to close unmatched angle bracket
 
-error: qualified paths cannot be used in associated type constraints
-  --> $DIR/trait-path-segments.rs:20:16
+error: expected one of `,`, `::`, `:`, or `>`, found `=`
+  --> $DIR/trait-path-segments.rs:20:35
    |
 LL |     impl<T : X<<Self as X>::Y<'a> = &'a u32>> Z for T {}
-   |                ^^^^^^^^^-^^^^^^^^
-   |                         |
-   |                         not allowed in associated type constraints
+   |                                 - ^ expected one of `,`, `::`, `:`, or `>`
+   |                                 |
+   |                                 maybe try to close unmatched angle bracket
 
-error: paths with multiple segments cannot be used in associated type constraints
-  --> $DIR/trait-path-segments.rs:31:16
+error: expected one of `!`, `+`, `,`, `::`, `:`, or `>`, found `=`
+  --> $DIR/trait-path-segments.rs:31:25
    |
 LL |     impl<T : X<X::Y<'a> = &'a u32>> Z for T {}
-   |                ^^^^^^^^
+   |                       - ^ expected one of `!`, `+`, `,`, `::`, `:`, or `>`
+   |                       |
+   |                       maybe try to close unmatched angle bracket
 
 warning: the feature `generic_associated_types` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/trait-path-segments.rs:1:12

src/test/ui/generic-associated-types/parse/trait-path-types.rs

@@ -7,17 +7,17 @@ trait X {
 
 const _: () = {
   fn f<'a>(arg : Box<dyn X< [u8; 1] = u32>>) {}
-      //~^ ERROR: only path types can be used in associated type constraints
+      //~^ ERROR: expected one of
 };
 
 const _: () = {
   fn f1<'a>(arg : Box<dyn X<(Y<'a>) = &'a ()>>) {}
-      //~^ ERROR: only path types can be used in associated type constraints
+      //~^ ERROR: expected one of
 };
 
 const _: () = {
   fn f1<'a>(arg : Box<dyn X< 'a = u32 >>) {}
-      //~^ ERROR: only types can be used in associated type constraints
+      //~^ ERROR: expected one of
 };
 
 fn main() {}

src/test/ui/generic-associated-types/parse/trait-path-types.stderr

@@ -1,20 +1,26 @@
-error: only path types can be used in associated type constraints
-  --> $DIR/trait-path-types.rs:9:29
+error: expected one of `,`, `:`, or `>`, found `=`
+  --> $DIR/trait-path-types.rs:9:37
    |
 LL |   fn f<'a>(arg : Box<dyn X< [u8; 1] = u32>>) {}
-   |                             ^^^^^^^
+   |                                   - ^ expected one of `,`, `:`, or `>`
+   |                                   |
+   |                                   maybe try to close unmatched angle bracket
 
-error: only path types can be used in associated type constraints
-  --> $DIR/trait-path-types.rs:14:29
+error: expected one of `,`, `:`, or `>`, found `=`
+  --> $DIR/trait-path-types.rs:14:37
    |
 LL |   fn f1<'a>(arg : Box<dyn X<(Y<'a>) = &'a ()>>) {}
-   |                             ^^^^^^^
+   |                                   - ^ expected one of `,`, `:`, or `>`
+   |                                   |
+   |                                   maybe try to close unmatched angle bracket
 
-error: only types can be used in associated type constraints
-  --> $DIR/trait-path-types.rs:19:30
+error: expected one of `,`, `:`, or `>`, found `=`
+  --> $DIR/trait-path-types.rs:19:33
    |
 LL |   fn f1<'a>(arg : Box<dyn X< 'a = u32 >>) {}
-   |                              ^^
+   |                              -- ^ expected one of `,`, `:`, or `>`
+   |                              |
+   |                              maybe try to close unmatched angle bracket
 
 warning: the feature `generic_associated_types` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/trait-path-types.rs:1:12

src/test/ui/issues/issue-34334.rs

@@ -1,6 +1,8 @@
 fn main () {
     let sr: Vec<(u32, _, _) = vec![];
-    //~^ ERROR only path types can be used in associated type constraints
+    //~^ ERROR expected one of
+
     let sr2: Vec<(u32, _, _)> = sr.iter().map(|(faction, th_sender, th_receiver)| {}).collect();
     //~^ ERROR a value of type `Vec<(u32, _, _)>` cannot be built
+
 }

src/test/ui/issues/issue-34334.stderr

@@ -1,13 +1,14 @@
-error: only path types can be used in associated type constraints
-  --> $DIR/issue-34334.rs:2:17
+error: expected one of `,`, `:`, or `>`, found `=`
+  --> $DIR/issue-34334.rs:2:29
    |
 LL |     let sr: Vec<(u32, _, _) = vec![];
-   |         --      ^^^^^^^^^^^
-   |         |
+   |         --                - ^ expected one of `,`, `:`, or `>`
+   |         |                 |
+   |         |                 maybe try to close unmatched angle bracket
    |         while parsing the type for `sr`
 
 error[E0277]: a value of type `Vec<(u32, _, _)>` cannot be built from an iterator over elements of type `()`
-  --> $DIR/issue-34334.rs:4:87
+  --> $DIR/issue-34334.rs:5:87
    |
 LL |     let sr2: Vec<(u32, _, _)> = sr.iter().map(|(faction, th_sender, th_receiver)| {}).collect();
    |                                                                                       ^^^^^^^ value of type `Vec<(u32, _, _)>` cannot be built from `std::iter::Iterator<Item=()>`

src/test/ui/parser/missing-closing-angle-bracket-eq-constraint.rs

@@ -0,0 +1,23 @@
+struct Foo<T1, T2> {
+  _a : T1,
+  _b : T2,
+}
+
+fn test1<T>(arg : T) {
+  let v : Vec<(u32,_) = vec![];
+    //~^ ERROR: expected one of
+    //~| ERROR: type annotations needed
+}
+
+fn test2<T1, T2>(arg1 : T1, arg2 : T2) {
+  let foo : Foo::<T1, T2 = Foo {_a : arg1, _b : arg2};
+    //~^ ERROR: expected one of
+}
+
+fn test3<'a>(arg : &'a u32) {
+  let v : Vec<'a = vec![];
+    //~^ ERROR: expected one of
+    //~| ERROR: type annotations needed for `Vec<T>`
+}
+
+fn main() {}