Rollup merge of #106540 - lowr:patch/remove-paren-whitespace, r=cjgillot

Insert whitespace to avoid ident concatenation in suggestion

This PR tweaks the suggestion of removing misplaced parentheses around trait bounds so as to avoid concatenating two identifiers. Although subtle, this should make outputs less surprising especially when applying the `MachineApplicable` suggestions automatically.

Author: matthiaskrgr

compiler/rustc_parse/src/parser/ty.rs

@@ -1048,7 +1048,7 @@ impl<'a> Parser<'a> {
                 self.parse_remaining_bounds(bounds, true)?;
                 self.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
                 let sp = vec![lo, self.prev_token.span];
-                let sugg: Vec<_> = sp.iter().map(|sp| (*sp, String::new())).collect();
+                let sugg = vec![(lo, String::from(" ")), (self.prev_token.span, String::new())];
                 self.struct_span_err(sp, "incorrect braces around trait bounds")
                     .multipart_suggestion(
                         "remove the parentheses",

tests/ui/parser/trait-object-delimiters.rs

@@ -5,6 +5,8 @@ fn foo1(_: &dyn Drop + AsRef<str>) {} //~ ERROR ambiguous `+` in a type
 
 fn foo2(_: &dyn (Drop + AsRef<str>)) {} //~ ERROR incorrect braces around trait bounds
 
+fn foo2_no_space(_: &dyn(Drop + AsRef<str>)) {} //~ ERROR incorrect braces around trait bounds
+
 fn foo3(_: &dyn {Drop + AsRef<str>}) {} //~ ERROR expected parameter name, found `{`
 //~^ ERROR expected one of `!`, `(`, `)`, `*`, `,`, `?`, `for`, `~`, lifetime, or path, found `{`
 //~| ERROR at least one trait is required for an object type

tests/ui/parser/trait-object-delimiters.stderr

@@ -13,31 +13,43 @@ LL | fn foo2(_: &dyn (Drop + AsRef<str>)) {}
 help: remove the parentheses
    |
 LL - fn foo2(_: &dyn (Drop + AsRef<str>)) {}
-LL + fn foo2(_: &dyn Drop + AsRef<str>) {}
+LL + fn foo2(_: &dyn  Drop + AsRef<str>) {}
+   |
+
+error: incorrect braces around trait bounds
+  --> $DIR/trait-object-delimiters.rs:8:25
+   |
+LL | fn foo2_no_space(_: &dyn(Drop + AsRef<str>)) {}
+   |                         ^                 ^
+   |
+help: remove the parentheses
+   |
+LL - fn foo2_no_space(_: &dyn(Drop + AsRef<str>)) {}
+LL + fn foo2_no_space(_: &dyn Drop + AsRef<str>) {}
    |
 
 error: expected parameter name, found `{`
-  --> $DIR/trait-object-delimiters.rs:8:17
+  --> $DIR/trait-object-delimiters.rs:10:17
    |
 LL | fn foo3(_: &dyn {Drop + AsRef<str>}) {}
    |                 ^ expected parameter name
 
 error: expected one of `!`, `(`, `)`, `*`, `,`, `?`, `for`, `~`, lifetime, or path, found `{`
-  --> $DIR/trait-object-delimiters.rs:8:17
+  --> $DIR/trait-object-delimiters.rs:10:17
    |
 LL | fn foo3(_: &dyn {Drop + AsRef<str>}) {}
    |                -^ expected one of 10 possible tokens
    |                |
    |                help: missing `,`
 
 error: expected identifier, found `<`
-  --> $DIR/trait-object-delimiters.rs:12:17
+  --> $DIR/trait-object-delimiters.rs:14:17
    |
 LL | fn foo4(_: &dyn <Drop + AsRef<str>>) {}
    |                 ^ expected identifier
 
 error: invalid `dyn` keyword
-  --> $DIR/trait-object-delimiters.rs:14:25
+  --> $DIR/trait-object-delimiters.rs:16:25
    |
 LL | fn foo5(_: &(dyn Drop + dyn AsRef<str>)) {}
    |                         ^^^ help: remove this keyword
@@ -56,13 +68,13 @@ LL | fn foo1(_: &dyn Drop + AsRef<str>) {}
    = note: auto-traits like `Send` and `Sync` are traits that have special properties; for more information on them, visit <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>
 
 error[E0224]: at least one trait is required for an object type
-  --> $DIR/trait-object-delimiters.rs:8:13
+  --> $DIR/trait-object-delimiters.rs:10:13
    |
 LL | fn foo3(_: &dyn {Drop + AsRef<str>}) {}
    |             ^^^
 
 error[E0225]: only auto traits can be used as additional traits in a trait object
-  --> $DIR/trait-object-delimiters.rs:14:29
+  --> $DIR/trait-object-delimiters.rs:16:29
    |
 LL | fn foo5(_: &(dyn Drop + dyn AsRef<str>)) {}
    |                  ----       ^^^^^^^^^^ additional non-auto trait
@@ -72,7 +84,7 @@ LL | fn foo5(_: &(dyn Drop + dyn AsRef<str>)) {}
    = help: consider creating a new trait with all of these as supertraits and using that trait here instead: `trait NewTrait: Drop + AsRef<str> {}`
    = note: auto-traits like `Send` and `Sync` are traits that have special properties; for more information on them, visit <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>
 
-error: aborting due to 9 previous errors
+error: aborting due to 10 previous errors
 
 Some errors have detailed explanations: E0224, E0225.
 For more information about an error, try `rustc --explain E0224`.