Rollup merge of #153967 - estebank:infer_must_implement, r=petrochenkov

Tweak wording of failed predicate in inference error

Special case message talking about `Predicate` that couldn't be satisfied when in inference errors so that we don't say "cannot satisfy `_: Trait`" and instead say "type must implement `Trait`".

compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs

@@ -11,6 +11,7 @@
 use rustc_infer::traits::{
     Obligation, ObligationCause, ObligationCauseCode, PolyTraitObligation, PredicateObligation,
 };
+use rustc_middle::ty::print::PrintPolyTraitPredicateExt;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable as _, TypeVisitableExt as _};
 use rustc_session::parse::feature_err_unstable_feature_bound;
 use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span};
@@ -306,8 +307,18 @@ pub(super) fn maybe_report_ambiguity(
                         err.cancel();
                         return e;
                     }
-                    let pred = self.tcx.short_string(predicate, &mut err.long_ty_path());
-                    err.note(format!("cannot satisfy `{pred}`"));
+                    if let Some(clause) = predicate.as_trait_clause()
+                        && let ty::Infer(_) = clause.self_ty().skip_binder().kind()
+                    {
+                        let tr = self.tcx.short_string(
+                            clause.print_modifiers_and_trait_path(),
+                            &mut err.long_ty_path(),
+                        );
+                        err.note(format!("the type must implement `{tr}`"));
+                    } else {
+                        let pred = self.tcx.short_string(predicate, &mut err.long_ty_path());
+                        err.note(format!("cannot satisfy `{pred}`"));
+                    }
                     let impl_candidates =
                         self.find_similar_impl_candidates(predicate.as_trait_clause().unwrap());
                     if impl_candidates.len() < 40 {

tests/ui/const-generics/issues/issue-83249.stderr

@@ -6,7 +6,7 @@ LL |     let _ = foo([0; 1]);
    |             |
    |             required by a bound introduced by this call
    |
-   = note: cannot satisfy `_: Foo`
+   = note: the type must implement `Foo`
 help: the trait `Foo` is implemented for `u8`
   --> $DIR/issue-83249.rs:8:1
    |

tests/ui/generic-associated-types/ambig-hr-projection-issue-93340.old.stderr

@@ -4,7 +4,7 @@ error[E0283]: type annotations needed
 LL |     cmp_eq
    |     ^^^^^^ cannot infer type of the type parameter `A` declared on the function `cmp_eq`
    |
-   = note: cannot satisfy `_: Scalar`
+   = note: the type must implement `Scalar`
 note: required by a bound in `cmp_eq`
   --> $DIR/ambig-hr-projection-issue-93340.rs:10:22
    |

tests/ui/generic-associated-types/bugs/issue-88382.stderr

@@ -4,7 +4,7 @@ error[E0283]: type annotations needed
 LL |     do_something(SomeImplementation(), test);
    |                                        ^^^^ cannot infer type of the type parameter `I` declared on the function `test`
    |
-   = note: cannot satisfy `_: Iterable`
+   = note: the type must implement `Iterable`
 help: the trait `Iterable` is implemented for `SomeImplementation`
   --> $DIR/issue-88382.rs:13:1
    |

tests/ui/impl-trait/in-trait/not-inferred-generic.stderr

@@ -4,7 +4,7 @@ error[E0283]: type annotations needed
 LL |     ().publish_typed();
    |        ^^^^^^^^^^^^^ cannot infer type of the type parameter `F` declared on the method `publish_typed`
    |
-   = note: cannot satisfy `_: Clone`
+   = note: the type must implement `Clone`
    = note: opaque types cannot be accessed directly on a `trait`, they can only be accessed through a specific `impl`
 note: required by a bound in `TypedClient::publish_typed::{anon_assoc#0}`
   --> $DIR/not-inferred-generic.rs:4:12

tests/ui/impl-trait/opaque-cast-field-access-in-future.stderr

@@ -7,7 +7,7 @@ LL |
 LL |     loop {}
    |     ------- return type was inferred to be `!` here
    |
-   = note: cannot satisfy `_: Future`
+   = note: the type must implement `Future`
 
 error: aborting due to 1 previous error
 

tests/ui/impl-trait/where-allowed-2.stderr

@@ -4,7 +4,7 @@ error[E0283]: type annotations needed
 LL | fn in_adt_in_return() -> Vec<impl Debug> { panic!() }
    |                              ^^^^^^^^^^ cannot infer type
    |
-   = note: cannot satisfy `_: Debug`
+   = note: the type must implement `Debug`
 
 error: aborting due to 1 previous error
 

tests/ui/impl-trait/where-allowed.stderr

@@ -374,7 +374,7 @@ error[E0283]: type annotations needed
 LL | fn in_dyn_Fn_return_in_return() -> &'static dyn Fn() -> impl Debug { panic!() }
    |                                                         ^^^^^^^^^^ cannot infer type
    |
-   = note: cannot satisfy `_: Debug`
+   = note: the type must implement `Debug`
 
 error[E0283]: type annotations needed
   --> $DIR/where-allowed.rs:65:46

tests/ui/imports/import-trait-method.stderr

@@ -14,7 +14,7 @@ error[E0283]: type annotations needed
 LL | fn main() { foo(); }
    |             ^^^^^ cannot infer type
    |
-   = note: cannot satisfy `_: Foo`
+   = note: the type must implement `Foo`
 
 error: aborting due to 2 previous errors
 

tests/ui/inference/erase-type-params-in-label.stderr

@@ -4,7 +4,7 @@ error[E0283]: type annotations needed for `Foo<i32, &str, _, _>`
 LL |     let foo = foo(1, "");
    |         ^^^   ---------- type must be known at this point
    |
-   = note: cannot satisfy `_: Default`
+   = note: the type must implement `Default`
 note: required by a bound in `foo`
   --> $DIR/erase-type-params-in-label.rs:25:17
    |
@@ -21,7 +21,7 @@ error[E0283]: type annotations needed for `Bar<i32, &str, _>`
 LL |     let bar = bar(1, "");
    |         ^^^   ---------- type must be known at this point
    |
-   = note: cannot satisfy `_: Default`
+   = note: the type must implement `Default`
 note: required by a bound in `bar`
   --> $DIR/erase-type-params-in-label.rs:14:17
    |

tests/ui/inference/issue-86162-1.stderr

@@ -6,7 +6,7 @@ LL |     foo(gen()); //<- Do not suggest `foo::<impl Clone>()`!
    |     |
    |     required by a bound introduced by this call
    |
-   = note: cannot satisfy `_: Clone`
+   = note: the type must implement `Clone`
 note: required by a bound in `foo`
   --> $DIR/issue-86162-1.rs:3:16
    |

tests/ui/inference/issue-86162-2.stderr

@@ -6,7 +6,7 @@ LL |     Foo::bar(gen()); //<- Do not suggest `Foo::bar::<impl Clone>()`!
    |     |
    |     required by a bound introduced by this call
    |
-   = note: cannot satisfy `_: Clone`
+   = note: the type must implement `Clone`
 note: required by a bound in `Foo::bar`
   --> $DIR/issue-86162-2.rs:8:20
    |

tests/ui/inference/need_type_info/issue-113264-incorrect-impl-trait-in-path-suggestion.stderr

@@ -6,7 +6,7 @@ LL |     (S {}).owo(None)
    |            |
    |            required by a bound introduced by this call
    |
-   = note: cannot satisfy `_: T`
+   = note: the type must implement `T`
 note: required by a bound in `S::owo`
   --> $DIR/issue-113264-incorrect-impl-trait-in-path-suggestion.rs:6:35
    |

tests/ui/inference/question-mark-type-infer.stderr

@@ -4,7 +4,7 @@ error[E0283]: type annotations needed
 LL |     l.iter().map(f).collect()?
    |                     ^^^^^^^ cannot infer type of the type parameter `B` declared on the method `collect`
    |
-   = note: cannot satisfy `_: FromIterator<Result<i32, ()>>`
+   = note: the type must implement `FromIterator<Result<i32, ()>>`
 note: required by a bound in `collect`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
 help: consider specifying the generic argument
@@ -18,7 +18,7 @@ error[E0283]: type annotations needed
 LL |     let x = l.iter().map(f).collect()?;
    |                             ^^^^^^^ cannot infer type of the type parameter `B` declared on the method `collect`
    |
-   = note: cannot satisfy `_: FromIterator<Result<i32, ()>>`
+   = note: the type must implement `FromIterator<Result<i32, ()>>`
 note: required by a bound in `collect`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
 help: consider specifying the generic argument
@@ -32,7 +32,7 @@ error[E0283]: type annotations needed
 LL |     let x: Vec<i32> = l.iter().map(f).collect()?;
    |                                       ^^^^^^^ cannot infer type of the type parameter `B` declared on the method `collect`
    |
-   = note: cannot satisfy `_: FromIterator<Result<i32, ()>>`
+   = note: the type must implement `FromIterator<Result<i32, ()>>`
 note: required by a bound in `collect`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
 help: consider specifying the generic argument

tests/ui/inference/question-mark-type-inference-in-chain.rs

@@ -41,7 +41,7 @@ pub fn error2(lines: &[&str]) -> Result<Vec<Version>> {
     let mut tags: Vec<Version> = lines.iter().map(|e| parse(e)).collect()?;
     //~^ ERROR: type annotations needed
     //~| NOTE: cannot infer type of the type parameter `B`
-    //~| NOTE: cannot satisfy `_: FromIterator<std::result::Result<Version, Error>>`
+    //~| NOTE: the type must implement `FromIterator<std::result::Result<Version, Error>>`
     //~| NOTE: required by a bound in `collect`
     //~| HELP: consider specifying the generic argument
     tags.sort();

tests/ui/inference/question-mark-type-inference-in-chain.stderr

@@ -18,7 +18,7 @@ error[E0283]: type annotations needed
 LL |     let mut tags: Vec<Version> = lines.iter().map(|e| parse(e)).collect()?;
    |                                                                 ^^^^^^^ cannot infer type of the type parameter `B` declared on the method `collect`
    |
-   = note: cannot satisfy `_: FromIterator<std::result::Result<Version, Error>>`
+   = note: the type must implement `FromIterator<std::result::Result<Version, Error>>`
 note: required by a bound in `collect`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
 help: consider specifying the generic argument

tests/ui/suggestions/types/into-inference-needs-type.stderr

@@ -4,7 +4,7 @@ error[E0283]: type annotations needed
 LL |         .into()?;
    |          ^^^^
    |
-   = note: cannot satisfy `_: From<FilterMap<Map<std::slice::Iter<'_, &str>, {closure@$DIR/into-inference-needs-type.rs:10:14: 10:17}>, fn(Option<&str>) -> Option<Option<&str>> {Option::<Option<&str>>::Some}>>`
+   = note: the type must implement `From<FilterMap<Map<std::slice::Iter<'_, &str>, {closure@$DIR/into-inference-needs-type.rs:10:14: 10:17}>, fn(Option<&str>) -> Option<Option<&str>> {Option::<Option<&str>>::Some}>>`
    = note: required for `FilterMap<Map<std::slice::Iter<'_, &str>, {closure@$DIR/into-inference-needs-type.rs:10:14: 10:17}>, fn(Option<&str>) -> Option<Option<&str>> {Option::<Option<&str>>::Some}>` to implement `Into<_>`
 help: try using a fully qualified path to specify the expected types
    |

tests/ui/trait-bounds/argument-with-unnecessary-method-call.stderr

@@ -6,7 +6,7 @@ LL |     qux(Bar.into());
    |     |
    |     required by a bound introduced by this call
    |
-   = note: cannot satisfy `_: From<Bar>`
+   = note: the type must implement `From<Bar>`
 note: required by a bound in `qux`
   --> $DIR/argument-with-unnecessary-method-call.rs:6:16
    |

tests/ui/traits/next-solver/assembly/runaway-impl-candidate-selection.stderr

@@ -4,7 +4,7 @@ error[E0283]: type annotations needed
 LL |     println!("{:?}", iter::<_>());
    |                      ^^^^^^^^^ cannot infer type of the type parameter `T` declared on the function `iter`
    |
-   = note: cannot satisfy `_: Iterator`
+   = note: the type must implement `Iterator`
 note: required by a bound in `iter`
   --> $DIR/runaway-impl-candidate-selection.rs:8:12
    |

tests/ui/traits/overflow-computing-ambiguity.stderr

@@ -4,7 +4,7 @@ error[E0283]: type annotations needed
 LL |     hello();
    |     ^^^^^ cannot infer type of the type parameter `T` declared on the function `hello`
    |
-   = note: cannot satisfy `_: Hello`
+   = note: the type must implement `Hello`
 help: the following types implement trait `Hello`
   --> $DIR/overflow-computing-ambiguity.rs:8:1
    |

tests/ui/type-inference/panic-with-unspecified-type.stderr

@@ -7,7 +7,7 @@ LL |     panic!(std::default::Default::default());
    |     |      cannot infer type
    |     required by a bound introduced by this call
    |
-   = note: cannot satisfy `_: Any`
+   = note: the type must implement `Any`
 note: required by a bound in `std::rt::begin_panic`
   --> $SRC_DIR/std/src/panicking.rs:LL:COL
 

tests/ui/type-inference/sort_by_key.stderr

@@ -6,7 +6,7 @@ LL |     lst.sort_by_key(|&(v, _)| v.iter().sum());
    |         |
    |         type must be known at this point
    |
-   = note: cannot satisfy `_: Ord`
+   = note: the type must implement `Ord`
 note: required by a bound in `slice::<impl [T]>::sort_by_key`
   --> $SRC_DIR/alloc/src/slice.rs:LL:COL
 help: consider specifying the generic argument

tests/ui/type/type-annotation-needed.rs

@@ -6,5 +6,5 @@ fn main() {
     foo(42);
     //~^ ERROR type annotations needed
     //~| NOTE cannot infer type
-    //~| NOTE cannot satisfy
+    //~| NOTE the type must implement
 }

tests/ui/type/type-annotation-needed.stderr

@@ -4,7 +4,7 @@ error[E0283]: type annotations needed
 LL |     foo(42);
    |     ^^^ cannot infer type of the type parameter `T` declared on the function `foo`
    |
-   = note: cannot satisfy `_: Into<String>`
+   = note: the type must implement `Into<String>`
 note: required by a bound in `foo`
   --> $DIR/type-annotation-needed.rs:1:11
    |