Rollup merge of #77855 - davidtwco:pr-77341-follow-up-non-constructable-variants, r=estebank

resolve: further improvements to "try using the enum's variant" diagnostic

Follow-up on https://github.com/rust-lang/rust/pull/77341#issuecomment-702738281.

This PR improves the diagnostic modified in #77341 to suggest not only those variants which do not have fields, but those with fields (by suggesting with placeholders). In addition, the wording of the tuple-variant-only case is improved slightly.

I've not made further changes to the tuple-variant-only case (e.g. to only suggest variants with the correct number of fields) because I don't think I have enough information to do so reliably (e.g. in the case where there is an attempt to construct a tuple variant, I have no information on how many fields were provided; and in the case of pattern matching, I only have a slice of spans and would need to check for things like `..` in those spans, which doesn't seem worth it).

r? @estebank

4 files changed, 230 insertions, 23 deletions

diff --git a/src/test/ui/did_you_mean/issue-43871-enum-instead-of-variant.stderr b/src/test/ui/did_you_mean/issue-43871-enum-instead-of-variant.stderr
index e1325b789d2..bca493e67d5 100644
--- a/src/test/ui/did_you_mean/issue-43871-enum-instead-of-variant.stderr
+++ b/src/test/ui/did_you_mean/issue-43871-enum-instead-of-variant.stderr
@@ -2,7 +2,7 @@ error[E0423]: expected function, tuple struct or tuple variant, found enum `Opti
   --> $DIR/issue-43871-enum-instead-of-variant.rs:19:13
    |
 LL |     let x = Option(1);
-   |             ^^^^^^ help: try using one of the enum's variants: `std::option::Option::Some`
+   |             ^^^^^^ help: try to construct one of the enum's variants: `std::option::Option::Some`
    |
    = help: you might have meant to construct the enum's non-tuple variant
 
@@ -10,7 +10,7 @@ error[E0532]: expected tuple struct or tuple variant, found enum `Option`
   --> $DIR/issue-43871-enum-instead-of-variant.rs:21:12
    |
 LL |     if let Option(_) = x {
-   |            ^^^^^^ help: try using one of the enum's variants: `std::option::Option::Some`
+   |            ^^^^^^ help: try to match against one of the enum's variants: `std::option::Option::Some`
    |
    = help: you might have meant to match against the enum's non-tuple variant
 
@@ -18,9 +18,14 @@ error[E0532]: expected tuple struct or tuple variant, found enum `Example`
   --> $DIR/issue-43871-enum-instead-of-variant.rs:27:12
    |
 LL |     if let Example(_) = y {
-   |            ^^^^^^^ help: try using one of the enum's variants: `Example::Ex`
+   |            ^^^^^^^ help: try to match against one of the enum's variants: `Example::Ex`
    |
    = help: you might have meant to match against the enum's non-tuple variant
+note: the enum is defined here
+  --> $DIR/issue-43871-enum-instead-of-variant.rs:1:1
+   |
+LL | enum Example { Ex(String), NotEx }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0423]: expected function, tuple struct or tuple variant, found enum `Void`
   --> $DIR/issue-43871-enum-instead-of-variant.rs:31:13
@@ -29,6 +34,11 @@ LL |     let y = Void();
    |             ^^^^
    |
    = help: the enum has no tuple variants to construct
+note: the enum is defined here
+  --> $DIR/issue-43871-enum-instead-of-variant.rs:3:1
+   |
+LL | enum Void {}
+   | ^^^^^^^^^^^^
 
 error[E0423]: expected function, tuple struct or tuple variant, found enum `ManyVariants`
   --> $DIR/issue-43871-enum-instead-of-variant.rs:33:13
@@ -38,6 +48,17 @@ LL |     let z = ManyVariants();
    |
    = help: the enum has no tuple variants to construct
    = help: you might have meant to construct one of the enum's non-tuple variants
+note: the enum is defined here
+  --> $DIR/issue-43871-enum-instead-of-variant.rs:5:1
+   |
+LL | / enum ManyVariants {
+LL | |     One,
+LL | |     Two,
+LL | |     Three,
+...  |
+LL | |     Ten,
+LL | | }
+   | |_^
 
 error: aborting due to 5 previous errors
 
diff --git a/src/test/ui/glob-resolve1.stderr b/src/test/ui/glob-resolve1.stderr
index 3c818f3ae48..cd128c1ea0b 100644
--- a/src/test/ui/glob-resolve1.stderr
+++ b/src/test/ui/glob-resolve1.stderr
@@ -24,7 +24,17 @@ error[E0423]: expected value, found enum `B`
   --> $DIR/glob-resolve1.rs:24:5
    |
 LL |     B;
-   |     ^ help: try using the enum's variant: `B::B1`
+   |     ^
+   |
+note: the enum is defined here
+  --> $DIR/glob-resolve1.rs:12:5
+   |
+LL |     pub enum B { B1 }
+   |     ^^^^^^^^^^^^^^^^^
+help: you might have meant to use the following enum variant
+   |
+LL |     B::B1;
+   |     ^^^^^
 
 error[E0425]: cannot find value `C` in this scope
   --> $DIR/glob-resolve1.rs:25:5
diff --git a/src/test/ui/issues/issue-73427.stderr b/src/test/ui/issues/issue-73427.stderr
index 88d19943f02..4b5f65b3461 100644
--- a/src/test/ui/issues/issue-73427.stderr
+++ b/src/test/ui/issues/issue-73427.stderr
@@ -4,8 +4,18 @@ error[E0423]: expected value, found enum `A`
 LL |     A.foo();
    |     ^
    |
-   = help: you might have meant to use one of the enum's other variants that have fields
-help: try using one of the enum's variants
+note: the enum is defined here
+  --> $DIR/issue-73427.rs:1:1
+   |
+LL | / enum A {
+LL | |     StructWithFields { x: () },
+LL | |     TupleWithFields(()),
+LL | |     Struct {},
+LL | |     Tuple(),
+LL | |     Unit,
+LL | | }
+   | |_^
+help: you might have meant to use one of the following enum variants
    |
 LL |     (A::Struct {}).foo();
    |     ^^^^^^^^^^^^^^
@@ -13,6 +23,12 @@ LL |     (A::Tuple()).foo();
    |     ^^^^^^^^^^^^
 LL |     A::Unit.foo();
    |     ^^^^^^^
+help: the following enum variants are available
+   |
+LL |     (A::StructWithFields { /* fields */ }).foo();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     (A::TupleWithFields(/* fields */)).foo();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0423]: expected value, found enum `B`
   --> $DIR/issue-73427.rs:31:5
@@ -20,23 +36,69 @@ error[E0423]: expected value, found enum `B`
 LL |     B.foo();
    |     ^
    |
-   = help: you might have meant to use one of the enum's variants
+note: the enum is defined here
+  --> $DIR/issue-73427.rs:9:1
+   |
+LL | / enum B {
+LL | |     StructWithFields { x: () },
+LL | |     TupleWithFields(()),
+LL | | }
+   | |_^
+help: the following enum variants are available
+   |
+LL |     (B::StructWithFields { /* fields */ }).foo();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     (B::TupleWithFields(/* fields */)).foo();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0423]: expected value, found enum `C`
   --> $DIR/issue-73427.rs:33:5
    |
 LL |     C.foo();
-   |     ^ help: try using one of the enum's variants: `C::Unit`
+   |     ^
+   |
+note: the enum is defined here
+  --> $DIR/issue-73427.rs:14:1
+   |
+LL | / enum C {
+LL | |     StructWithFields { x: () },
+LL | |     TupleWithFields(()),
+LL | |     Unit,
+LL | | }
+   | |_^
+help: you might have meant to use the following enum variant
+   |
+LL |     C::Unit.foo();
+   |     ^^^^^^^
+help: the following enum variants are available
    |
-   = help: you might have meant to use one of the enum's other variants that have fields
+LL |     (C::StructWithFields { /* fields */ }).foo();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     (C::TupleWithFields(/* fields */)).foo();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0423]: expected value, found enum `D`
   --> $DIR/issue-73427.rs:35:5
    |
 LL |     D.foo();
-   |     ^ help: try using one of the enum's variants: `D::Unit`
+   |     ^
+   |
+note: the enum is defined here
+  --> $DIR/issue-73427.rs:20:1
+   |
+LL | / enum D {
+LL | |     TupleWithFields(()),
+LL | |     Unit,
+LL | | }
+   | |_^
+help: you might have meant to use the following enum variant
    |
-   = help: you might have meant to use the enum's other variant that has fields
+LL |     D::Unit.foo();
+   |     ^^^^^^^
+help: the following enum variant is available
+   |
+LL |     (D::TupleWithFields(/* fields */)).foo();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0423]: expected function, tuple struct or tuple variant, found enum `A`
   --> $DIR/issue-73427.rs:40:13
@@ -45,7 +107,18 @@ LL |     let x = A(3);
    |             ^
    |
    = help: you might have meant to construct one of the enum's non-tuple variants
-help: try using one of the enum's variants
+note: the enum is defined here
+  --> $DIR/issue-73427.rs:1:1
+   |
+LL | / enum A {
+LL | |     StructWithFields { x: () },
+LL | |     TupleWithFields(()),
+LL | |     Struct {},
+LL | |     Tuple(),
+LL | |     Unit,
+LL | | }
+   | |_^
+help: try to construct one of the enum's variants
    |
 LL |     let x = A::TupleWithFields(3);
    |             ^^^^^^^^^^^^^^^^^^
@@ -59,7 +132,18 @@ LL |     if let A(3) = x { }
    |            ^
    |
    = help: you might have meant to match against one of the enum's non-tuple variants
-help: try using one of the enum's variants
+note: the enum is defined here
+  --> $DIR/issue-73427.rs:1:1
+   |
+LL | / enum A {
+LL | |     StructWithFields { x: () },
+LL | |     TupleWithFields(()),
+LL | |     Struct {},
+LL | |     Tuple(),
+LL | |     Unit,
+LL | | }
+   | |_^
+help: try to match against one of the enum's variants
    |
 LL |     if let A::TupleWithFields(3) = x { }
    |            ^^^^^^^^^^^^^^^^^^
diff --git a/src/test/ui/resolve/privacy-enum-ctor.stderr b/src/test/ui/resolve/privacy-enum-ctor.stderr
index 77429f800f1..807dadf417b 100644
--- a/src/test/ui/resolve/privacy-enum-ctor.stderr
+++ b/src/test/ui/resolve/privacy-enum-ctor.stderr
@@ -2,17 +2,57 @@ error[E0423]: expected value, found enum `n::Z`
   --> $DIR/privacy-enum-ctor.rs:23:9
    |
 LL |         n::Z;
-   |         ^^^^ help: try using one of the enum's variants: `m::Z::Unit`
+   |         ^^^^
    |
-   = help: you might have meant to use one of the enum's other variants that have fields
+note: the enum is defined here
+  --> $DIR/privacy-enum-ctor.rs:11:9
+   |
+LL | /         pub(in m) enum Z {
+LL | |             Fn(u8),
+LL | |             Struct {
+LL | |                 s: u8,
+LL | |             },
+LL | |             Unit,
+LL | |         }
+   | |_________^
+help: you might have meant to use the following enum variant
+   |
+LL |         m::Z::Unit;
+   |         ^^^^^^^^^^
+help: the following enum variants are available
+   |
+LL |         (m::Z::Fn(/* fields */));
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         (m::Z::Struct { /* fields */ });
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0423]: expected value, found enum `Z`
   --> $DIR/privacy-enum-ctor.rs:25:9
    |
 LL |         Z;
-   |         ^ help: try using one of the enum's variants: `m::Z::Unit`
+   |         ^
+   |
+note: the enum is defined here
+  --> $DIR/privacy-enum-ctor.rs:11:9
    |
-   = help: you might have meant to use one of the enum's other variants that have fields
+LL | /         pub(in m) enum Z {
+LL | |             Fn(u8),
+LL | |             Struct {
+LL | |                 s: u8,
+LL | |             },
+LL | |             Unit,
+LL | |         }
+   | |_________^
+help: you might have meant to use the following enum variant
+   |
+LL |         m::Z::Unit;
+   |         ^^^^^^^^^^
+help: the following enum variants are available
+   |
+LL |         (m::Z::Fn(/* fields */));
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         (m::Z::Struct { /* fields */ });
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0423]: expected value, found struct variant `Z::Struct`
   --> $DIR/privacy-enum-ctor.rs:29:20
@@ -34,11 +74,27 @@ LL |     fn f() {
 LL |     let _: E = m::E;
    |                ^^^^
    |
-   = help: you might have meant to use one of the enum's other variants that have fields
-help: try using one of the enum's variants
+note: the enum is defined here
+  --> $DIR/privacy-enum-ctor.rs:2:5
+   |
+LL | /     pub enum E {
+LL | |         Fn(u8),
+LL | |         Struct {
+LL | |             s: u8,
+LL | |         },
+LL | |         Unit,
+LL | |     }
+   | |_____^
+help: you might have meant to use the following enum variant
    |
 LL |     let _: E = E::Unit;
    |                ^^^^^^^
+help: the following enum variants are available
+   |
+LL |     let _: E = (E::Fn(/* fields */));
+   |                ^^^^^^^^^^^^^^^^^^^^^
+LL |     let _: E = (E::Struct { /* fields */ });
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 help: a function with a similar name exists
    |
 LL |     let _: E = m::f;
@@ -67,11 +123,27 @@ error[E0423]: expected value, found enum `E`
 LL |     let _: E = E;
    |                ^
    |
-   = help: you might have meant to use one of the enum's other variants that have fields
-help: try using one of the enum's variants
+note: the enum is defined here
+  --> $DIR/privacy-enum-ctor.rs:2:5
+   |
+LL | /     pub enum E {
+LL | |         Fn(u8),
+LL | |         Struct {
+LL | |             s: u8,
+LL | |         },
+LL | |         Unit,
+LL | |     }
+   | |_____^
+help: you might have meant to use the following enum variant
    |
 LL |     let _: E = E::Unit;
    |                ^^^^^^^
+help: the following enum variants are available
+   |
+LL |     let _: E = (E::Fn(/* fields */));
+   |                ^^^^^^^^^^^^^^^^^^^^^
+LL |     let _: E = (E::Struct { /* fields */ });
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 help: consider importing one of these items instead
    |
 LL | use std::f32::consts::E;
@@ -112,9 +184,29 @@ error[E0423]: expected value, found enum `m::n::Z`
   --> $DIR/privacy-enum-ctor.rs:57:16
    |
 LL |     let _: Z = m::n::Z;
-   |                ^^^^^^^ help: try using one of the enum's variants: `m::Z::Unit`
+   |                ^^^^^^^
+   |
+note: the enum is defined here
+  --> $DIR/privacy-enum-ctor.rs:11:9
+   |
+LL | /         pub(in m) enum Z {
+LL | |             Fn(u8),
+LL | |             Struct {
+LL | |                 s: u8,
+LL | |             },
+LL | |             Unit,
+LL | |         }
+   | |_________^
+help: you might have meant to use the following enum variant
+   |
+LL |     let _: Z = m::Z::Unit;
+   |                ^^^^^^^^^^
+help: the following enum variants are available
    |
-   = help: you might have meant to use one of the enum's other variants that have fields
+LL |     let _: Z = (m::Z::Fn(/* fields */));
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     let _: Z = (m::Z::Struct { /* fields */ });
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0412]: cannot find type `Z` in this scope
   --> $DIR/privacy-enum-ctor.rs:61:12