Rollup merge of rust-lang#97109 - TaKO8Ki:fix-misleading-cannot-infer-type-for-type-parameter-error, r=oli-obk

Fix misleading `cannot infer type for type parameter` error closes rust-lang#93198

Author: matthiaskrgr

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -866,6 +866,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
  }
  }
 
+ self.report_ambiguous_type_parameter(&mut err, arg);
  err.span_label(
  span,
  arg_data.cannot_infer_msg(use_diag.filter(|d| d.applies_to(span))),
@@ -933,6 +934,28 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
  }
  }
 
+ fn report_ambiguous_type_parameter(&self, err: &mut Diagnostic, arg: GenericArg<'tcx>) {
+ if let GenericArgKind::Type(ty) = arg.unpack()
+ && let ty::Infer(ty::TyVar(ty_vid)) = *ty.kind()
+ {
+ let mut inner = self.inner.borrow_mut();
+ let ty_vars = &inner.type_variables();
+ let var_origin = ty_vars.var_origin(ty_vid);
+ if let TypeVariableOriginKind::TypeParameterDefinition(_, Some(def_id)) =
+ var_origin.kind
+ && let Some(parent_def_id) = self.tcx.parent(def_id).as_local()
+ && let Some(node) = self.tcx.hir().find_by_def_id(parent_def_id)
+ {
+ match node {
+ hir::Node::Item(item) if matches!(item.kind, hir::ItemKind::Impl(_) | hir::ItemKind::Fn(..)) => (),
+ hir::Node::ImplItem(impl_item) if matches!(impl_item.kind, hir::ImplItemKind::Fn(..)) => (),
+ _ => return,
+ }
+ err.span_help(self.tcx.def_span(def_id), "type parameter declared here");
+ }
+ }
+ }
+
  pub fn need_type_info_err_in_generator(
  &self,
  kind: hir::GeneratorKind,

src/test/ui/const-generics/issues/issue-83249.stderr

@@ -5,6 +5,12 @@ LL | let _ = foo([0; 1]);
  | - ^^^ cannot infer type for type parameter `T` declared on the function `foo`
  | |
  | consider giving this pattern a type
+ |
+help: type parameter declared here
+ --> $DIR/issue-83249.rs:12:8
+ |
+LL | fn foo<T: Foo>(_: [u8; T::N]) -> T {
+ | ^
 
 error: aborting due to previous error
 

src/test/ui/consts/issue-64662.stderr

@@ -3,12 +3,24 @@ error[E0282]: type annotations needed
  |
 LL | A = foo(),
  | ^^^ cannot infer type for type parameter `T` declared on the function `foo`
+ |
+help: type parameter declared here
+ --> $DIR/issue-64662.rs:6:14
+ |
+LL | const fn foo<T>() -> isize {
+ | ^
 
 error[E0282]: type annotations needed
  --> $DIR/issue-64662.rs:3:9
  |
 LL | B = foo(),
  | ^^^ cannot infer type for type parameter `T` declared on the function `foo`
+ |
+help: type parameter declared here
+ --> $DIR/issue-64662.rs:6:14
+ |
+LL | const fn foo<T>() -> isize {
+ | ^
 
 error: aborting due to 2 previous errors
 

src/test/ui/error-codes/E0401.stderr

@@ -37,6 +37,12 @@ error[E0282]: type annotations needed
  |
 LL | bfnr(x);
  | ^^^^ cannot infer type for type parameter `U` declared on the function `bfnr`
+ |
+help: type parameter declared here
+ --> $DIR/E0401.rs:4:13
+ |
+LL | fn bfnr<U, V: Baz<U>, W: Fn()>(y: T) {
+ | ^
 
 error: aborting due to 4 previous errors
 

src/test/ui/inference/ambiguous_type_parameter.rs

@@ -0,0 +1,17 @@
+use std::collections::HashMap;
+
+trait Store<K, V> {
+ fn get_raw(&self, key: &K) -> Option<()>;
+}
+
+struct InMemoryStore;
+
+impl<K> Store<String, HashMap<K, String>> for InMemoryStore {
+ fn get_raw(&self, key: &String) -> Option<()> {
+ None
+ }
+}
+
+fn main() {
+ InMemoryStore.get_raw(&String::default()); //~ ERROR type annotations needed
+}

src/test/ui/inference/ambiguous_type_parameter.stderr

@@ -0,0 +1,15 @@
+error[E0282]: type annotations needed
+ --> $DIR/ambiguous_type_parameter.rs:16:19
+ |
+LL | InMemoryStore.get_raw(&String::default());
+ | ^^^^^^^ cannot infer type for type parameter `K`
+ |
+help: type parameter declared here
+ --> $DIR/ambiguous_type_parameter.rs:9:6
+ |
+LL | impl<K> Store<String, HashMap<K, String>> for InMemoryStore {
+ | ^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0282`.

src/test/ui/inference/erase-type-params-in-label.stderr

@@ -6,6 +6,11 @@ LL | let foo = foo(1, "");
  | |
  | consider giving `foo` the explicit type `Foo<_, _, W, Z>`, where the type parameter `W` is specified
  |
+help: type parameter declared here
+ --> $DIR/erase-type-params-in-label.rs:25:14
+ |
+LL | fn foo<T, K, W: Default, Z: Default>(t: T, k: K) -> Foo<T, K, W, Z> {
+ | ^
  = note: cannot satisfy `_: Default`
 note: required by a bound in `foo`
  --> $DIR/erase-type-params-in-label.rs:25:17
@@ -25,6 +30,11 @@ LL | let bar = bar(1, "");
  | |
  | consider giving `bar` the explicit type `Bar<_, _, Z>`, where the type parameter `Z` is specified
  |
+help: type parameter declared here
+ --> $DIR/erase-type-params-in-label.rs:14:14
+ |
+LL | fn bar<T, K, Z: Default>(t: T, k: K) -> Bar<T, K, Z> {
+ | ^
  = note: cannot satisfy `_: Default`
 note: required by a bound in `bar`
  --> $DIR/erase-type-params-in-label.rs:14:17

src/test/ui/inference/issue-86162-1.stderr

@@ -4,6 +4,11 @@ error[E0283]: type annotations needed
 LL | foo(gen()); //<- Do not suggest `foo::<impl Clone>()`!
  | ^^^ cannot infer type for type parameter `impl Clone` declared on the function `foo`
  |
+help: type parameter declared here
+ --> $DIR/issue-86162-1.rs:3:11
+ |
+LL | fn foo(x: impl Clone) {}
+ | ^^^^^^^^^^
  = note: cannot satisfy `_: Clone`
 note: required by a bound in `foo`
  --> $DIR/issue-86162-1.rs:3:16

src/test/ui/inference/issue-86162-2.stderr

@@ -4,6 +4,11 @@ error[E0283]: type annotations needed
 LL | Foo::bar(gen()); //<- Do not suggest `Foo::bar::<impl Clone>()`!
  | ^^^^^^^^ cannot infer type for type parameter `impl Clone` declared on the associated function `bar`
  |
+help: type parameter declared here
+ --> $DIR/issue-86162-2.rs:8:15
+ |
+LL | fn bar(x: impl Clone) {}
+ | ^^^^^^^^^^
  = note: cannot satisfy `_: Clone`
 note: required by a bound in `Foo::bar`
  --> $DIR/issue-86162-2.rs:8:20

src/test/ui/issues/issue-6458.stderr

@@ -3,6 +3,12 @@ error[E0282]: type annotations needed
  |
 LL | foo(TypeWithState(marker::PhantomData));
  | ^^^ cannot infer type for type parameter `State` declared on the function `foo`
+ |
+help: type parameter declared here
+ --> $DIR/issue-6458.rs:6:12
+ |
+LL | pub fn foo<State>(_: TypeWithState<State>) {}
+ | ^^^^^
 
 error: aborting due to previous error