Do not suggest "is a function" for free variables

Part of #82323

compiler/rustc_typeck/src/check/method/suggest.rs

@@ -40,7 +40,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  Err(..) => return false,
  };
 
+ // This conditional prevents us from asking to call errors and unresolved types.
+ // It might seem that we can use `predicate_must_hold_modulo_regions`,
+ // but since a Dummy binder is used to fill in the FnOnce trait's arguments,
+ // type resolution always gives a "maybe" here.
+ if self.autoderef(span, ty).any(|(ty, _)| {
+ info!("check deref {:?} error", ty);
+ matches!(ty.kind(), ty::Error(_) | ty::Infer(_))
+ }) {
+ return false;
+ }
+
  self.autoderef(span, ty).any(|(ty, _)| {
+ info!("check deref {:?} impl FnOnce", ty);
  self.probe(|_| {
  let fn_once_substs = tcx.mk_substs_trait(
  ty,

src/test/ui/functions-closures/fn-help-with-err-generic-is-not-function.rs

@@ -0,0 +1,22 @@
+struct Struct<T>(T);
+impl Struct<T>
+//~^ ERROR cannot find type `T` in this scope
+//~| NOTE not found in this scope
+//~| HELP you might be missing a type parameter
+where
+ T: Copy,
+ //~^ ERROR cannot find type `T` in this scope
+ //~| NOTE not found in this scope
+{
+ // The part where it claims that there is no method named `len` is a bug. Feel free to fix it.
+ // This test is intended to ensure that a different bug, where it claimed
+ // that `v` was a function, does not regress.
+ fn method(v: Vec<u8>) { v.len(); }
+ //~^ ERROR type annotations needed
+ //~| NOTE cannot infer type
+ //~| NOTE type must be known at this point
+ //~| ERROR no method named `len`
+ //~| NOTE private field, not a method
+}
+
+fn main() {}

src/test/ui/functions-closures/fn-help-with-err-generic-is-not-function.stderr

@@ -0,0 +1,32 @@
+error[E0412]: cannot find type `T` in this scope
+ --> $DIR/fn-help-with-err-generic-is-not-function.rs:2:13
+ |
+LL | impl Struct<T>
+ | - ^ not found in this scope
+ | |
+ | help: you might be missing a type parameter: `<T>`
+
+error[E0412]: cannot find type `T` in this scope
+ --> $DIR/fn-help-with-err-generic-is-not-function.rs:7:5
+ |
+LL | T: Copy,
+ | ^ not found in this scope
+
+error[E0282]: type annotations needed
+ --> $DIR/fn-help-with-err-generic-is-not-function.rs:14:31
+ |
+LL | fn method(v: Vec<u8>) { v.len(); }
+ | ^^^ cannot infer type
+ |
+ = note: type must be known at this point
+
+error[E0599]: no method named `len` found for struct `Vec<u8>` in the current scope
+ --> $DIR/fn-help-with-err-generic-is-not-function.rs:14:31
+ |
+LL | fn method(v: Vec<u8>) { v.len(); }
+ | ^^^ private field, not a method
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0282, E0412, E0599.
+For more information about an error, try `rustc --explain E0282`.

src/test/ui/functions-closures/fn-help-with-err.rs

@@ -0,0 +1,16 @@
+// This test case checks the behavior of typeck::check::method::suggest::is_fn on Ty::Error.
+fn main() {
+ let arc = std::sync::Arc::new(oops);
+ //~^ ERROR cannot find value `oops` in this scope
+ //~| NOTE not found
+ // The error "note: `arc` is a function, perhaps you wish to call it" MUST NOT appear.
+ arc.blablabla();
+ //~^ ERROR no method named `blablabla`
+ //~| NOTE method not found
+ let arc2 = std::sync::Arc::new(|| 1);
+ // The error "note: `arc2` is a function, perhaps you wish to call it" SHOULD appear
+ arc2.blablabla();
+ //~^ ERROR no method named `blablabla`
+ //~| NOTE method not found
+ //~| NOTE `arc2` is a function, perhaps you wish to call it
+}

src/test/ui/functions-closures/fn-help-with-err.stderr

@@ -0,0 +1,24 @@
+error[E0425]: cannot find value `oops` in this scope
+ --> $DIR/fn-help-with-err.rs:3:35
+ |
+LL | let arc = std::sync::Arc::new(oops);
+ | ^^^^ not found in this scope
+
+error[E0599]: no method named `blablabla` found for struct `Arc<_>` in the current scope
+ --> $DIR/fn-help-with-err.rs:7:9
+ |
+LL | arc.blablabla();
+ | ^^^^^^^^^ method not found in `Arc<_>`
+
+error[E0599]: no method named `blablabla` found for struct `Arc<[closure@$DIR/fn-help-with-err.rs:10:36: 10:40]>` in the current scope
+ --> $DIR/fn-help-with-err.rs:12:10
+ |
+LL | arc2.blablabla();
+ | ^^^^^^^^^ method not found in `Arc<[closure@$DIR/fn-help-with-err.rs:10:36: 10:40]>`
+ |
+ = note: `arc2` is a function, perhaps you wish to call it
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0425, E0599.
+For more information about an error, try `rustc --explain E0425`.