Suggest : Type instead of : _

Author: estebank

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] {""}
 }
 

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,

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
 

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
 

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
 

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
 

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
 

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

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
 

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