Suggest `: Type` instead of `: _`

20 files changed, 79 insertions, 75 deletions

diff --git a/compiler/rustc_error_messages/locales/en-US/infer.ftl b/compiler/rustc_error_messages/locales/en-US/infer.ftl
index c9d83746d54..fbef2da7cb9 100644
--- a/compiler/rustc_error_messages/locales/en-US/infer.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/infer.ftl
@@ -34,6 +34,7 @@ infer_source_kind_subdiag_let = {$kind ->
         [const] the value of the constant
     } `{$arg_name}` is specified
     [underscore] , where the placeholders `_` are specified
+    [anon] , where the placeholder `Type` is specified
     *[empty] {""}
 }
 
diff --git a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
index 41e7a0608af..38655492244 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
@@ -77,13 +77,15 @@ impl InferenceDiagnosticsData {
         !(self.name == "_" && matches!(self.kind, UnderspecifiedArgKind::Type { .. }))
     }
 
-    fn where_x_is_kind(&self, in_type: Ty<'_>) -> &'static str {
-        if self.name == "_" {
+    fn where_x_is_kind(&self, in_type: Ty<'_>, is_collect: bool) -> &'static str {
+        if is_collect {
+            "empty"
+        } else if in_type.is_ty_infer() {
+            "anon"
+        } else if self.name == "_" {
             // FIXME: Consider specializing this message if there is a single `_`
             // in the type.
             "underscore"
-        } else if in_type.is_ty_infer() {
-            "empty"
         } else {
             "has_name"
         }
@@ -190,6 +192,7 @@ fn ty_to_string<'tcx>(infcx: &InferCtxt<'tcx>, ty: Ty<'tcx>) -> String {
         // We don't want the regular output for `fn`s because it includes its path in
         // invalid pseudo-syntax, we want the `fn`-pointer output instead.
         ty::FnDef(..) => ty.fn_sig(infcx.tcx).print(printer).unwrap().into_buffer(),
+        _ if ty.is_ty_infer() => "Type".to_string(),
         // FIXME: The same thing for closures, but this only works when the closure
         // does not capture anything.
         //
@@ -411,7 +414,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 infer_subdiags.push(SourceKindSubdiag::LetLike {
                     span: insert_span,
                     name: pattern_name.map(|name| name.to_string()).unwrap_or_else(String::new),
-                    x_kind: if is_collect { "empty" } else { arg_data.where_x_is_kind(ty) },
+                    x_kind: arg_data.where_x_is_kind(ty, is_collect),
                     prefix_kind: arg_data.kind.clone(),
                     prefix: arg_data.kind.try_get_prefix().unwrap_or_default(),
                     arg_name: arg_data.name,
@@ -427,7 +430,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 infer_subdiags.push(SourceKindSubdiag::LetLike {
                     span: insert_span,
                     name: String::new(),
-                    x_kind: arg_data.where_x_is_kind(ty),
+                    x_kind: arg_data.where_x_is_kind(ty, false),
                     prefix_kind: arg_data.kind.clone(),
                     prefix: arg_data.kind.try_get_prefix().unwrap_or_default(),
                     arg_name: arg_data.name,
diff --git a/src/test/ui/array-slice-vec/infer_array_len.stderr b/src/test/ui/array-slice-vec/infer_array_len.stderr
index bd757be126c..11a07164e8c 100644
--- a/src/test/ui/array-slice-vec/infer_array_len.stderr
+++ b/src/test/ui/array-slice-vec/infer_array_len.stderr
@@ -4,10 +4,10 @@ error[E0282]: type annotations needed
 LL |     let [_, _] = a.into();
    |         ^^^^^^
    |
-help: consider giving this pattern a type, where the placeholders `_` are specified
+help: consider giving this pattern a type, where the placeholder `Type` is specified
    |
-LL |     let [_, _]: _ = a.into();
-   |               +++
+LL |     let [_, _]: Type = a.into();
+   |               ++++++
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/closure-expected-type/expect-two-infer-vars-supply-ty-with-bound-region.stderr b/src/test/ui/closure-expected-type/expect-two-infer-vars-supply-ty-with-bound-region.stderr
index d5432755cfe..9e5705ba00b 100644
--- a/src/test/ui/closure-expected-type/expect-two-infer-vars-supply-ty-with-bound-region.stderr
+++ b/src/test/ui/closure-expected-type/expect-two-infer-vars-supply-ty-with-bound-region.stderr
@@ -4,10 +4,10 @@ error[E0282]: type annotations needed
 LL |     with_closure(|x: u32, y| {});
    |                           ^
    |
-help: consider giving this closure parameter an explicit type
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |     with_closure(|x: u32, y: _| {});
-   |                            +++
+LL |     with_closure(|x: u32, y: Type| {});
+   |                            ++++++
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/closures/issue-52437.stderr b/src/test/ui/closures/issue-52437.stderr
index f7d34890a79..c635e743293 100644
--- a/src/test/ui/closures/issue-52437.stderr
+++ b/src/test/ui/closures/issue-52437.stderr
@@ -10,10 +10,10 @@ error[E0282]: type annotations needed
 LL |     [(); &(&'static: loop { |x| {}; }) as *const _ as usize]
    |                              ^
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |     [(); &(&'static: loop { |x: _| {}; }) as *const _ as usize]
-   |                               +++
+LL |     [(); &(&'static: loop { |x: Type| {}; }) as *const _ as usize]
+   |                               ++++++
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/const-generics/issues/issue-83249.stderr b/src/test/ui/const-generics/issues/issue-83249.stderr
index 362b8554b2f..f148cb7699e 100644
--- a/src/test/ui/const-generics/issues/issue-83249.stderr
+++ b/src/test/ui/const-generics/issues/issue-83249.stderr
@@ -4,10 +4,10 @@ error[E0282]: type annotations needed
 LL |     let _ = foo([0; 1]);
    |         ^
    |
-help: consider giving this pattern a type
+help: consider giving this pattern a type, where the placeholder `Type` is specified
    |
-LL |     let _: _ = foo([0; 1]);
-   |          +++
+LL |     let _: Type = foo([0; 1]);
+   |          ++++++
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/impl-trait/issues/issue-86719.stderr b/src/test/ui/impl-trait/issues/issue-86719.stderr
index da184c26bfe..30bad841d15 100644
--- a/src/test/ui/impl-trait/issues/issue-86719.stderr
+++ b/src/test/ui/impl-trait/issues/issue-86719.stderr
@@ -18,10 +18,10 @@ error[E0282]: type annotations needed
 LL |         |_| true
    |          ^
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |         |_: _| true
-   |           +++
+LL |         |_: Type| true
+   |           ++++++
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/inference/issue-72690.stderr b/src/test/ui/inference/issue-72690.stderr
index e59bcea9512..37daeb6441f 100644
--- a/src/test/ui/inference/issue-72690.stderr
+++ b/src/test/ui/inference/issue-72690.stderr
@@ -30,10 +30,10 @@ error[E0282]: type annotations needed
 LL |     |x| String::from("x".as_ref());
    |      ^
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |     |x: _| String::from("x".as_ref());
-   |       +++
+LL |     |x: Type| String::from("x".as_ref());
+   |       ++++++
 
 error[E0283]: type annotations needed
   --> $DIR/issue-72690.rs:12:26
diff --git a/src/test/ui/issues/issue-18159.stderr b/src/test/ui/issues/issue-18159.stderr
index bedfeda2ea0..1cfb0e41504 100644
--- a/src/test/ui/issues/issue-18159.stderr
+++ b/src/test/ui/issues/issue-18159.stderr
@@ -4,10 +4,10 @@ error[E0282]: type annotations needed
 LL |     let x;
    |         ^
    |
-help: consider giving `x` an explicit type, where the placeholders `_` are specified
+help: consider giving `x` an explicit type, where the placeholder `Type` is specified
    |
-LL |     let x: _;
-   |          +++
+LL |     let x: Type;
+   |          ++++++
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-2151.stderr b/src/test/ui/issues/issue-2151.stderr
index 411fdc48344..f689afd4ea7 100644
--- a/src/test/ui/issues/issue-2151.stderr
+++ b/src/test/ui/issues/issue-2151.stderr
@@ -6,10 +6,10 @@ LL |     let x = panic!();
 LL |     x.clone();
    |     - type must be known at this point
    |
-help: consider giving `x` an explicit type, where the placeholders `_` are specified
+help: consider giving `x` an explicit type, where the placeholder `Type` is specified
    |
-LL |     let x: _ = panic!();
-   |          +++
+LL |     let x: Type = panic!();
+   |          ++++++
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-24036.stderr b/src/test/ui/issues/issue-24036.stderr
index fcfce56bcb1..2413db2cada 100644
--- a/src/test/ui/issues/issue-24036.stderr
+++ b/src/test/ui/issues/issue-24036.stderr
@@ -17,10 +17,10 @@ error[E0282]: type annotations needed
 LL |         1 => |c| c + 1,
    |               ^
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |         1 => |c: _| c + 1,
-   |                +++
+LL |         1 => |c: Type| c + 1,
+   |                ++++++
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/lazy-type-alias-impl-trait/branches3.stderr b/src/test/ui/lazy-type-alias-impl-trait/branches3.stderr
index 9d56d96c8c1..d14cad4d71c 100644
--- a/src/test/ui/lazy-type-alias-impl-trait/branches3.stderr
+++ b/src/test/ui/lazy-type-alias-impl-trait/branches3.stderr
@@ -4,10 +4,10 @@ error[E0282]: type annotations needed
 LL |         |s| s.len()
    |          ^  - type must be known at this point
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |         |s: _| s.len()
-   |           +++
+LL |         |s: Type| s.len()
+   |           ++++++
 
 error[E0282]: type annotations needed
   --> $DIR/branches3.rs:15:10
@@ -15,10 +15,10 @@ error[E0282]: type annotations needed
 LL |         |s| s.len()
    |          ^  - type must be known at this point
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |         |s: _| s.len()
-   |           +++
+LL |         |s: Type| s.len()
+   |           ++++++
 
 error[E0282]: type annotations needed
   --> $DIR/branches3.rs:23:10
@@ -26,10 +26,10 @@ error[E0282]: type annotations needed
 LL |         |s| s.len()
    |          ^  - type must be known at this point
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |         |s: _| s.len()
-   |           +++
+LL |         |s: Type| s.len()
+   |           ++++++
 
 error[E0282]: type annotations needed
   --> $DIR/branches3.rs:30:10
@@ -37,10 +37,10 @@ error[E0282]: type annotations needed
 LL |         |s| s.len()
    |          ^  - type must be known at this point
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |         |s: _| s.len()
-   |           +++
+LL |         |s: Type| s.len()
+   |           ++++++
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/match/match-unresolved-one-arm.stderr b/src/test/ui/match/match-unresolved-one-arm.stderr
index db5db38391e..0ebd56cb064 100644
--- a/src/test/ui/match/match-unresolved-one-arm.stderr
+++ b/src/test/ui/match/match-unresolved-one-arm.stderr
@@ -4,10 +4,10 @@ error[E0282]: type annotations needed
 LL |     let x = match () {
    |         ^
    |
-help: consider giving `x` an explicit type, where the placeholders `_` are specified
+help: consider giving `x` an explicit type, where the placeholder `Type` is specified
    |
-LL |     let x: _ = match () {
-   |          +++
+LL |     let x: Type = match () {
+   |          ++++++
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/pattern/pat-tuple-bad-type.stderr b/src/test/ui/pattern/pat-tuple-bad-type.stderr
index 86fd1e0c196..ff45e9fb7a3 100644
--- a/src/test/ui/pattern/pat-tuple-bad-type.stderr
+++ b/src/test/ui/pattern/pat-tuple-bad-type.stderr
@@ -7,10 +7,10 @@ LL |     let x;
 LL |         (..) => {}
    |         ---- type must be known at this point
    |
-help: consider giving `x` an explicit type, where the placeholders `_` are specified
+help: consider giving `x` an explicit type, where the placeholder `Type` is specified
    |
-LL |     let x: _;
-   |          +++
+LL |     let x: Type;
+   |          ++++++
 
 error[E0308]: mismatched types
   --> $DIR/pat-tuple-bad-type.rs:10:9
diff --git a/src/test/ui/pattern/rest-pat-semantic-disallowed.stderr b/src/test/ui/pattern/rest-pat-semantic-disallowed.stderr
index 5bf168a5711..df0aa942fed 100644
--- a/src/test/ui/pattern/rest-pat-semantic-disallowed.stderr
+++ b/src/test/ui/pattern/rest-pat-semantic-disallowed.stderr
@@ -191,10 +191,10 @@ error[E0282]: type annotations needed
 LL |     let x @ ..;
    |         ^^^^^^
    |
-help: consider giving this pattern a type, where the placeholders `_` are specified
+help: consider giving this pattern a type, where the placeholder `Type` is specified
    |
-LL |     let x @ ..: _;
-   |               +++
+LL |     let x @ ..: Type;
+   |               ++++++
 
 error: aborting due to 23 previous errors
 
diff --git a/src/test/ui/resolve/issue-85348.stderr b/src/test/ui/resolve/issue-85348.stderr
index cc9cd3fe68b..2cbc109055f 100644
--- a/src/test/ui/resolve/issue-85348.stderr
+++ b/src/test/ui/resolve/issue-85348.stderr
@@ -19,10 +19,10 @@ error[E0282]: type annotations needed
 LL |         let mut N;
    |             ^^^^^
    |
-help: consider giving `N` an explicit type, where the placeholders `_` are specified
+help: consider giving `N` an explicit type, where the placeholder `Type` is specified
    |
-LL |         let mut N: _;
-   |                  +++
+LL |         let mut N: Type;
+   |                  ++++++
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/span/method-and-field-eager-resolution.stderr b/src/test/ui/span/method-and-field-eager-resolution.stderr
index 85205464626..554a2580c94 100644
--- a/src/test/ui/span/method-and-field-eager-resolution.stderr
+++ b/src/test/ui/span/method-and-field-eager-resolution.stderr
@@ -7,10 +7,10 @@ LL |
 LL |     x.0;
    |     - type must be known at this point
    |
-help: consider giving `x` an explicit type, where the placeholders `_` are specified
+help: consider giving `x` an explicit type, where the placeholder `Type` is specified
    |
-LL |     let mut x: _ = Default::default();
-   |              +++
+LL |     let mut x: Type = Default::default();
+   |              ++++++
 
 error[E0282]: type annotations needed
   --> $DIR/method-and-field-eager-resolution.rs:11:9
@@ -21,10 +21,10 @@ LL |
 LL |     x[0];
    |     - type must be known at this point
    |
-help: consider giving `x` an explicit type, where the placeholders `_` are specified
+help: consider giving `x` an explicit type, where the placeholder `Type` is specified
    |
-LL |     let mut x: _ = Default::default();
-   |              +++
+LL |     let mut x: Type = Default::default();
+   |              ++++++
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/type-alias-impl-trait/closures_in_branches.stderr b/src/test/ui/type-alias-impl-trait/closures_in_branches.stderr
index 6f8b5cc4cc5..0d7341bfb91 100644
--- a/src/test/ui/type-alias-impl-trait/closures_in_branches.stderr
+++ b/src/test/ui/type-alias-impl-trait/closures_in_branches.stderr
@@ -4,10 +4,10 @@ error[E0282]: type annotations needed
 LL |         |x| x.len()
    |          ^  - type must be known at this point
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |         |x: _| x.len()
-   |           +++
+LL |         |x: Type| x.len()
+   |           ++++++
 
 error[E0282]: type annotations needed
   --> $DIR/closures_in_branches.rs:21:10
@@ -15,10 +15,10 @@ error[E0282]: type annotations needed
 LL |         |x| x.len()
    |          ^  - type must be known at this point
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |         |x: _| x.len()
-   |           +++
+LL |         |x: Type| x.len()
+   |           ++++++
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/type/type-check/unknown_type_for_closure.stderr b/src/test/ui/type/type-check/unknown_type_for_closure.stderr
index 2ba5f07a8f4..01e053ccd51 100644
--- a/src/test/ui/type/type-check/unknown_type_for_closure.stderr
+++ b/src/test/ui/type/type-check/unknown_type_for_closure.stderr
@@ -10,10 +10,10 @@ error[E0282]: type annotations needed
 LL |     let x = |_| {};
    |              ^
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |     let x = |_: _| {};
-   |               +++
+LL |     let x = |_: Type| {};
+   |               ++++++
 
 error[E0282]: type annotations needed
   --> $DIR/unknown_type_for_closure.rs:10:14
diff --git a/src/test/ui/type/type-path-err-node-types.stderr b/src/test/ui/type/type-path-err-node-types.stderr
index 24cc4a2a761..51077dedbbe 100644
--- a/src/test/ui/type/type-path-err-node-types.stderr
+++ b/src/test/ui/type/type-path-err-node-types.stderr
@@ -28,10 +28,10 @@ error[E0282]: type annotations needed
 LL |     let _ = |a, b: _| -> _ { 0 };
    |              ^
    |
-help: consider giving this closure parameter an explicit type, where the placeholders `_` are specified
+help: consider giving this closure parameter an explicit type, where the placeholder `Type` is specified
    |
-LL |     let _ = |a: _, b: _| -> _ { 0 };
-   |               +++
+LL |     let _ = |a: Type, b: _| -> _ { 0 };
+   |               ++++++
 
 error: aborting due to 5 previous errors