Suggest replacing . with :: in more error diagnostics.

[zachs18]

First commit makes the existing "help: use the path separator to refer to an item" also work when the base is a type alias, not just a trait/module/struct.

The existing unconditional DefKind::Mod | DefKind::Trait match arm is changed to a conditional DefKind::Mod | DefKind::Trait | DefKind::TyAlias arm that only matches if the path_sep suggestion-adding closure succeeds, so as not to stop the later DefKind::TyAlias-specific suggestions if the path-sep suggestion does not apply. This shouldn't change behavior for Mod or Trait (due to the default arm's return false etc).

This commit also updates tests/ui/resolve/issue-22692.rs to reflect this, and also renames it to something more meaningful.

This commit also makes the bad_struct_syntax_suggestion closure take err as a parameter instead of capturing it, since otherwise caused borrowing errors due to the change to using path_sep in a pattern guard.

Type alias diagnostic example

type S = String;

fn main() {
    let _ = S.new;
}

 error[E0423]: expected value, found type alias `S`
  --> diag7.rs:4:13
   |
 4 |     let _ = S.new;
   |             ^
   |
-  = note: can't use a type alias as a constructor
+  help: use the path separator to refer to an item
+  |
+4 |     let _ = S::new;
+  |              ~~

Second commit adds some cases for enums, where if there is a field/method expression where the field/method has the name of a unit/tuple variant, we assume the user intended to create that variant¹ and suggest replacing the . from the field/method suggestion with a :: path separator. If no such variant is found (or if the error is not a field/method expression), we give the existing suggestion that suggests adding ::TupleVariant(/* fields */) after the enum.

Enum diagnostic example

enum Foo {
    A(u32),
    B,
    C { x: u32 },
}

fn main() {
    let _ = Foo.A(42); // changed
    let _ = Foo.B;     // changed
    let _ = Foo.D(42); // no change
    let _ = Foo.D;     // no change
    let _ = Foo(42);   // no change
}

 error[E0423]: expected value, found enum `Foo`
  --> diag8.rs:8:13
   |
 8 |     let _ = Foo.A(42); // changed
   |             ^^^
   |
 note: the enum is defined here
  --> diag8.rs:1:1
   |
 1 | / enum Foo {
 2 | |     A(u32),
 3 | |     B,
 4 | |     C { x: u32 },
 5 | | }
   | |_^
-help: you might have meant to use the following enum variant
-  |
-8 |     let _ = Foo::B.A(42); // changed
-  |             ~~~~~~
-help: alternatively, the following enum variant is available
+help: use the path separator to refer to a variant
   |
-8 |     let _ = (Foo::A(/* fields */)).A(42); // changed
-  |             ~~~~~~~~~~~~~~~~~~~~~~
+8 |     let _ = Foo::A(42); // changed
+  |                ~~
 
 error[E0423]: expected value, found enum `Foo`
  --> diag8.rs:9:13
   |
 9 |     let _ = Foo.B;     // changed
   |             ^^^
   |
 note: the enum is defined here
  --> diag8.rs:1:1
   |
 1 | / enum Foo {
 2 | |     A(u32),
 3 | |     B,
 4 | |     C { x: u32 },
 5 | | }
   | |_^
-help: you might have meant to use the following enum variant
-  |
-9 |     let _ = Foo::B.B;     // changed
-  |             ~~~~~~
-help: alternatively, the following enum variant is available
+help: use the path separator to refer to a variant
   |
-9 |     let _ = (Foo::A(/* fields */)).B;     // changed
-  |             ~~~~~~~~~~~~~~~~~~~~~~
+9 |     let _ = Foo::B;     // changed
+  |                ~~
 
 error[E0423]: expected value, found enum `Foo`
   --> diag8.rs:10:13
    |
 10 |     let _ = Foo.D(42); // no change
    |             ^^^
    |
 note: the enum is defined here
   --> diag8.rs:1:1
    |
 1  | / enum Foo {
 2  | |     A(u32),
 3  | |     B,
 4  | |     C { x: u32 },
 5  | | }
    | |_^
 help: you might have meant to use the following enum variant
    |
 10 |     let _ = Foo::B.D(42); // no change
    |             ~~~~~~
 help: alternatively, the following enum variant is available
    |
 10 |     let _ = (Foo::A(/* fields */)).D(42); // no change
    |             ~~~~~~~~~~~~~~~~~~~~~~
 
 error[E0423]: expected value, found enum `Foo`
   --> diag8.rs:11:13
    |
 11 |     let _ = Foo.D;     // no change
    |             ^^^
    |
 note: the enum is defined here
   --> diag8.rs:1:1
    |
 1  | / enum Foo {
 2  | |     A(u32),
 3  | |     B,
 4  | |     C { x: u32 },
 5  | | }
    | |_^
 help: you might have meant to use the following enum variant
    |
 11 |     let _ = Foo::B.D;     // no change
    |             ~~~~~~
 help: alternatively, the following enum variant is available
    |
 11 |     let _ = (Foo::A(/* fields */)).D;     // no change
    |             ~~~~~~~~~~~~~~~~~~~~~~
 
 error[E0423]: expected function, tuple struct or tuple variant, found enum `Foo`
   --> diag8.rs:12:13
    |
 12 |     let _ = Foo(42);   // no change
    |             ^^^ help: try to construct one of the enum's variants: `Foo::A`
    |
    = help: you might have meant to construct the enum's non-tuple variant
 note: the enum is defined here
   --> diag8.rs:1:1
    |
 1  | / enum Foo {
 2  | |     A(u32),
 3  | |     B,
 4  | |     C { x: u32 },
 5  | | }
    | |_^
 
 error: aborting due to 5 previous errors

Footnotes

1. or if it's a field expression and a tuple variant, that they meant to refer the variant constructor. ↩

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[zachs18]

If the enum diagnostics aren't worth it I'm fine dropping them from the PR, the type alias one is my main reason for the PR.

[davidtwco]

@bors r+

[bors]

📌 Commit 4b94807 has been approved by davidtwco

It is now in the queue for this repository.

[jieyouxu]

I think this failed in rollup: https://github.com/rust-lang/rust/actions/runs/13396817895/job/37417817710?pr=137236

 ---- [ui] tests/ui/resolve/enum-expected-value-suggest-variants.rs stdout ----
[...]
  diff of stderr:
  
  105	   | |_^
  106	help: you might have meant to use one of the following enum variants
  107	   |
  -	LL -     let _: Bar = Bar.Bad(0);
  -	LL +     let _: Bar = Bar::E.Bad(0);

@bors r-

[zachs18]

Probably from #136958 . Latest push should fix it.

[davidtwco]

@bors r+

[bors]

📌 Commit 2c37250 has been approved by davidtwco

It is now in the queue for this repository.