cool beans

Author: lcnr

compiler/rustc_middle/src/query/mod.rs

@@ -1412,6 +1412,10 @@ rustc_queries! {
         separate_provide_extern
     }
 
+    query is_general_impl(def_id: DefId) -> bool {
+        desc { |tcx| "looking up whether `{}` is a general impl", tcx.def_path_str(def_id) }
+    }
+
     query check_well_formed(key: LocalDefId) -> () {
         desc { |tcx| "checking that `{}` is well-formed", tcx.def_path_str(key.to_def_id()) }
     }

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -135,8 +135,23 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // candidate which assumes $0 == int, one that assumes `$0 ==
         // usize`, etc. This spells an ambiguity.
 
-        let mut candidates = self.filter_impls(candidates, stack.obligation);
-
+        let candidates = self.filter_impls(candidates, stack.obligation);
+        let mut candidates = candidates
+            .into_iter()
+            .map(|c| match c {
+                ImplCandidate(impl_def) if self.tcx().is_general_impl(impl_def) => {
+                    match self.evaluate_candidate(stack, &c) {
+                        Ok(eval) if eval.may_apply() => Ok(Some(c)),
+                        Ok(_) => Ok(None),
+                        Err(OverflowError::Canonical) => Err(Overflow(OverflowError::Canonical)),
+                        Err(OverflowError::ErrorReporting) => Err(ErrorReporting),
+                        Err(OverflowError::Error(e)) => Err(Overflow(OverflowError::Error(e))),
+                    }
+                }
+                _ => Ok(Some(c)),
+            })
+            .flat_map(Result::transpose)
+            .collect::<Result<Vec<_>, _>>()?;
         // If there is more than one candidate, first winnow them down
         // by considering extra conditions (nested obligations and so
         // forth). We don't winnow if there is exactly one

compiler/rustc_ty_utils/src/ty.rs

@@ -2,6 +2,7 @@ use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::subst::Subst;
+use rustc_middle::ty::util::IgnoreRegions;
 use rustc_middle::ty::{
     self, Binder, EarlyBinder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt,
 };
@@ -460,6 +461,13 @@ pub fn conservative_is_privately_uninhabited_raw<'tcx>(
     }
 }
 
+fn is_general_impl(tcx: TyCtxt<'_>, id: DefId) -> bool {
+    let Some(trait_ref) = tcx.impl_trait_ref(id) else {
+        span_bug!(tcx.def_span(id), "expected impl, found `{:?} for `{:?}`", tcx.def_kind(id), id);
+    };
+    tcx.uses_unique_generic_params(trait_ref.substs, IgnoreRegions::No).is_ok()
+}
+
 pub fn provide(providers: &mut ty::query::Providers) {
     *providers = ty::query::Providers {
         asyncness,
@@ -469,6 +477,7 @@ pub fn provide(providers: &mut ty::query::Providers) {
         instance_def_size_estimate,
         issue33140_self_ty,
         impl_defaultness,
+        is_general_impl,
         conservative_is_privately_uninhabited: conservative_is_privately_uninhabited_raw,
         ..*providers
     };

library/core/src/future/into_future.rs

@@ -99,6 +99,11 @@ use crate::future::Future;
 /// }
 /// ```
 #[stable(feature = "into_future", since = "1.64.0")]
+#[rustc_on_unimplemented(
+    label = "`{Self}` cannot be converted to a future",
+    message = "`{Self}` cannot be converted to a future",
+    note = "{Self} must be a future or must implement `IntoFuture` to be awaited"
+)]
 pub trait IntoFuture {
     /// The output that the future will produce on completion.
     #[stable(feature = "into_future", since = "1.64.0")]

library/core/src/iter/traits/collect.rs

@@ -227,6 +227,35 @@ pub trait FromIterator<A>: Sized {
 /// ```
 #[rustc_diagnostic_item = "IntoIterator"]
 #[rustc_skip_array_during_method_dispatch]
+#[rustc_on_unimplemented(
+    on(
+        _Self = "std::ops::RangeTo<Idx>",
+        label = "if you meant to iterate until a value, add a starting value",
+        note = "`..end` is a `RangeTo`, which cannot be iterated on; you might have meant to have a \
+              bounded `Range`: `0..end`"
+    ),
+    on(
+        _Self = "std::ops::RangeToInclusive<Idx>",
+        label = "if you meant to iterate until a value (including it), add a starting value",
+        note = "`..=end` is a `RangeToInclusive`, which cannot be iterated on; you might have meant \
+              to have a bounded `RangeInclusive`: `0..=end`"
+    ),
+    on(
+        _Self = "&str",
+        label = "cannot implicitly convert `{Self}` to an iterator; try calling `.chars()` or `.bytes()`"
+    ),
+    on(
+        _Self = "std::string::String",
+        label = "cannot implicitly convert `{Self}` to an iterator; try calling `.chars()` or `.bytes()`"
+    ),
+    on(
+        _Self = "{integral}",
+        note = "if you want to iterate between `start` until a value `end`, use the exclusive range \
+              syntax `start..end` or the inclusive range syntax `start..=end`"
+    ),
+    label = "`{Self}` cannot be converted to an iterator",
+    message = "`{Self}` cannot be converted to an iterator"
+)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait IntoIterator {
     /// The type of the elements being iterated over.

src/test/ui/associated-types/substs-ppaux.normal.stderr

@@ -70,18 +70,11 @@ help: use parentheses to call this function
 LL |     let x: () = foo::<'static>();
    |                               ++
 
-error[E0277]: the size for values of type `str` cannot be known at compilation time
+error[E0277]: the trait bound `str: Foo<'_, '_, u8>` is not satisfied
   --> $DIR/substs-ppaux.rs:49:5
    |
 LL |     <str as Foo<u8>>::bar;
-   |     ^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `str`
-note: required because of the requirements on the impl of `Foo<'_, '_, u8>` for `str`
-  --> $DIR/substs-ppaux.rs:11:17
-   |
-LL | impl<'a,'b,T,S> Foo<'a, 'b, S> for T {}
-   |                 ^^^^^^^^^^^^^^     ^
+   |     ^^^^^^^^^^^^^^^^^^^^^ the trait `Foo<'_, '_, u8>` is not implemented for `str`
 
 error: aborting due to 5 previous errors
 

src/test/ui/associated-types/substs-ppaux.verbose.stderr

@@ -70,18 +70,11 @@ help: use parentheses to call this function
 LL |     let x: () = foo::<'static>();
    |                               ++
 
-error[E0277]: the size for values of type `str` cannot be known at compilation time
+error[E0277]: the trait bound `str: Foo<'_#0r, '_#1r, u8>` is not satisfied
   --> $DIR/substs-ppaux.rs:49:5
    |
 LL |     <str as Foo<u8>>::bar;
-   |     ^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `str`
-note: required because of the requirements on the impl of `Foo<'_#0r, '_#1r, u8>` for `str`
-  --> $DIR/substs-ppaux.rs:11:17
-   |
-LL | impl<'a,'b,T,S> Foo<'a, 'b, S> for T {}
-   |                 ^^^^^^^^^^^^^^     ^
+   |     ^^^^^^^^^^^^^^^^^^^^^ the trait `Foo<'_#0r, '_#1r, u8>` is not implemented for `str`
 
 error: aborting due to 5 previous errors
 

src/test/ui/async-await/issue-70594.stderr

@@ -18,15 +18,14 @@ error[E0744]: `.await` is not allowed in a `const`
 LL |     [1; ().await];
    |           ^^^^^^
 
-error[E0277]: `()` is not a future
+error[E0277]: `()` cannot be converted to a future
   --> $DIR/issue-70594.rs:4:11
    |
 LL |     [1; ().await];
-   |           ^^^^^^ `()` is not a future
+   |           ^^^^^^ `()` cannot be converted to a future
    |
-   = help: the trait `Future` is not implemented for `()`
+   = help: the trait `IntoFuture` is not implemented for `()`
    = note: () must be a future or must implement `IntoFuture` to be awaited
-   = note: required because of the requirements on the impl of `IntoFuture` for `()`
 help: remove the `.await`
    |
 LL -     [1; ().await];

src/test/ui/async-await/issues/issue-62009-1.stderr

@@ -24,15 +24,14 @@ LL | fn main() {
 LL |     (|_| 2333).await;
    |               ^^^^^^ only allowed inside `async` functions and blocks
 
-error[E0277]: `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]` is not a future
+error[E0277]: `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]` cannot be converted to a future
   --> $DIR/issue-62009-1.rs:12:15
    |
 LL |     (|_| 2333).await;
-   |               ^^^^^^ `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]` is not a future
+   |               ^^^^^^ `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]` cannot be converted to a future
    |
-   = help: the trait `Future` is not implemented for `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]`
+   = help: the trait `IntoFuture` is not implemented for `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]`
    = note: [closure@$DIR/issue-62009-1.rs:12:6: 12:9] must be a future or must implement `IntoFuture` to be awaited
-   = note: required because of the requirements on the impl of `IntoFuture` for `[closure@$DIR/issue-62009-1.rs:12:6: 12:9]`
 help: remove the `.await`
    |
 LL -     (|_| 2333).await;

src/test/ui/async-await/unnecessary-await.stderr

@@ -1,14 +1,13 @@
-error[E0277]: `()` is not a future
+error[E0277]: `()` cannot be converted to a future
   --> $DIR/unnecessary-await.rs:9:10
    |
 LL |     boo().await;
-   |     -----^^^^^^ `()` is not a future
+   |     -----^^^^^^ `()` cannot be converted to a future
    |     |
    |     this call returns `()`
    |
-   = help: the trait `Future` is not implemented for `()`
+   = help: the trait `IntoFuture` is not implemented for `()`
    = note: () must be a future or must implement `IntoFuture` to be awaited
-   = note: required because of the requirements on the impl of `IntoFuture` for `()`
 help: remove the `.await`
    |
 LL -     boo().await;