Auto merge of rust-lang#79606 - ThePuzzlemaker:issue-79458-fix, r=scottmcm

bors · bors · commit d37afad0cc87 · 2020-12-02T07:37:40.000Z
Do not show negative polarity trait implementations in diagnostic messages for similar implementations This fixes rust-lang#79458. Previously, this code: ```rust #[derive(Clone)] struct Foo<'a, T> { x: &'a mut T, } ``` would have suggested that `<&mut T as Clone>` was an implementation that was found. This is due to the fact that the standard library now has `impl<'_, T> !Clone for &'_ mut T`, and explicit negative polarity implementations were not filtered out in diagnostic output when suggesting similar implementations. This PR fixes this issue by filtering out negative polarity trait implementations in `find_similar_impl_candidates` within `rustc_trait_selection::traits::error_reporting::InferCtxtPrivExt<'tcx>`. It also adds a UI regression test for this issue and fixes UI tests that had incorrectly been modified to expect the invalid output. r? `@scottmcm`
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -1310,10 +1310,20 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
                             return None;
                         }
                     }
+                    if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative {
+                        return None;
+                    }
                     Some(imp)
                 })
                 .collect(),
-            None => all_impls.map(|def_id| self.tcx.impl_trait_ref(def_id).unwrap()).collect(),
+            None => all_impls
+                .filter_map(|def_id| {
+                    if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative {
+                        return None;
+                    }
+                    self.tcx.impl_trait_ref(def_id)
+                })
+                .collect(),
         }
     }
 
diff --git a/src/test/ui/associated-types/hr-associated-type-bound-1.stderr b/src/test/ui/associated-types/hr-associated-type-bound-1.stderr
@@ -12,7 +12,6 @@ LL |     type U = str;
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/associated-types/hr-associated-type-bound-object.stderr b/src/test/ui/associated-types/hr-associated-type-bound-object.stderr
@@ -12,7 +12,6 @@ LL | fn f<'a, T: X<'a> + ?Sized>(x: &<T as X<'a>>::U) {
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/associated-types/hr-associated-type-bound-param-1.stderr b/src/test/ui/associated-types/hr-associated-type-bound-param-1.stderr
@@ -12,7 +12,6 @@ LL |     type V = str;
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/associated-types/hr-associated-type-bound-param-2.stderr b/src/test/ui/associated-types/hr-associated-type-bound-param-2.stderr
@@ -12,7 +12,6 @@ LL |     for<'b> <T as Z<'b, u16>>::W: Clone,
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error[E0277]: the trait bound `for<'b> <u16 as Z<'b, u16>>::W: Clone` is not satisfied
   --> $DIR/hr-associated-type-bound-param-2.rs:16:14
@@ -28,7 +27,6 @@ LL |     type W = str;
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error[E0277]: the trait bound `for<'b> <u16 as Z<'b, u16>>::W: Clone` is not satisfied
   --> $DIR/hr-associated-type-bound-param-2.rs:4:8
@@ -44,7 +42,6 @@ LL |     for<'b> <T as Z<'b, u16>>::W: Clone,
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/associated-types/hr-associated-type-bound-param-3.stderr b/src/test/ui/associated-types/hr-associated-type-bound-param-3.stderr
@@ -12,7 +12,6 @@ LL |     type U = str;
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/associated-types/hr-associated-type-bound-param-4.stderr b/src/test/ui/associated-types/hr-associated-type-bound-param-4.stderr
@@ -12,7 +12,6 @@ LL |     type U = str;
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/associated-types/hr-associated-type-bound-param-5.stderr b/src/test/ui/associated-types/hr-associated-type-bound-param-5.stderr
@@ -12,7 +12,6 @@ LL |     type U = str;
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error[E0277]: the trait bound `for<'b> <Vec<T> as X<'b, Vec<T>>>::U: Clone` is not satisfied
   --> $DIR/hr-associated-type-bound-param-5.rs:27:14
@@ -28,7 +27,6 @@ LL |     type U = str;
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error[E0277]: the trait bound `for<'b> <Vec<T> as X<'b, Vec<T>>>::U: Clone` is not satisfied
   --> $DIR/hr-associated-type-bound-param-5.rs:33:14
@@ -44,7 +42,6 @@ LL |     type U = str;
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error[E0277]: the trait bound `for<'b> <Box<T> as X<'b, Box<T>>>::U: Clone` is not satisfied
   --> $DIR/hr-associated-type-bound-param-5.rs:33:14
@@ -60,7 +57,6 @@ LL |     type U = str;
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/associated-types/hr-associated-type-bound-param-6.stderr b/src/test/ui/associated-types/hr-associated-type-bound-param-6.stderr
@@ -12,7 +12,6 @@ LL |     type U = str;
    |
    = help: the following implementations were found:
              <&T as Clone>
-             <&mut T as Clone>
 
 error[E0277]: the trait bound `for<'b> T: X<'b, T>` is not satisfied
   --> $DIR/hr-associated-type-bound-param-6.rs:12:12
diff --git a/src/test/ui/async-await/issue-64130-3-other.stderr b/src/test/ui/async-await/issue-64130-3-other.stderr
@@ -10,8 +10,6 @@ LL | async fn bar() {
 LL |     is_qux(bar());
    |     ^^^^^^ within `impl Future`, the trait `Qux` is not implemented for `Foo`
    |
-   = help: the following implementations were found:
-             <Foo as Qux>
 note: future does not implement `Qux` as this value is used across an await
   --> $DIR/issue-64130-3-other.rs:18:5
    |
diff --git a/src/test/ui/auto-traits/typeck-default-trait-impl-constituent-types-2.stderr b/src/test/ui/auto-traits/typeck-default-trait-impl-constituent-types-2.stderr
@@ -7,8 +7,6 @@ LL | fn is_mytrait<T: MyTrait>() {}
 LL |     is_mytrait::<(MyS2, MyS)>();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^ within `(MyS2, MyS)`, the trait `MyTrait` is not implemented for `MyS2`
    |
-   = help: the following implementations were found:
-             <MyS2 as MyTrait>
    = note: required because it appears within the type `(MyS2, MyS)`
 
 error: aborting due to previous error
diff --git a/src/test/ui/auto-traits/typeck-default-trait-impl-constituent-types.stderr b/src/test/ui/auto-traits/typeck-default-trait-impl-constituent-types.stderr
@@ -6,9 +6,6 @@ LL | fn is_mytrait<T: MyTrait>() {}
 ...
 LL |     is_mytrait::<MyS2>();
    |                  ^^^^ the trait `MyTrait` is not implemented for `MyS2`
-   |
-   = help: the following implementations were found:
-             <MyS2 as MyTrait>
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/auto-traits/typeck-default-trait-impl-negation.stderr b/src/test/ui/auto-traits/typeck-default-trait-impl-negation.stderr
@@ -6,9 +6,6 @@ LL | fn is_my_trait<T: MyTrait>() {}
 ...
 LL |     is_my_trait::<ThisImplsUnsafeTrait>();
    |                   ^^^^^^^^^^^^^^^^^^^^ the trait `MyTrait` is not implemented for `ThisImplsUnsafeTrait`
-   |
-   = help: the following implementations were found:
-             <ThisImplsUnsafeTrait as MyTrait>
 
 error[E0277]: the trait bound `ThisImplsTrait: MyUnsafeTrait` is not satisfied
   --> $DIR/typeck-default-trait-impl-negation.rs:25:26
@@ -18,9 +15,6 @@ LL | fn is_my_unsafe_trait<T: MyUnsafeTrait>() {}
 ...
 LL |     is_my_unsafe_trait::<ThisImplsTrait>();
    |                          ^^^^^^^^^^^^^^ the trait `MyUnsafeTrait` is not implemented for `ThisImplsTrait`
-   |
-   = help: the following implementations were found:
-             <ThisImplsTrait as MyUnsafeTrait>
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/traits/issue-79458.rs b/src/test/ui/traits/issue-79458.rs
@@ -0,0 +1,10 @@
+// Negative implementations should not be shown in trait suggestions.
+// This is a regression test of #79458.
+
+#[derive(Clone)]
+struct Foo<'a, T> {
+    bar: &'a mut T
+    //~^ ERROR the trait bound `&mut T: Clone` is not satisfied
+}
+
+fn main() {}
diff --git a/src/test/ui/traits/issue-79458.stderr b/src/test/ui/traits/issue-79458.stderr
@@ -0,0 +1,15 @@
+error[E0277]: the trait bound `&mut T: Clone` is not satisfied
+  --> $DIR/issue-79458.rs:6:5
+   |
+LL |     bar: &'a mut T
+   |     ^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `&mut T`
+   |
+   = help: the following implementations were found:
+             <&T as Clone>
+   = note: `Clone` is implemented for `&T`, but not for `&mut T`
+   = note: required by `clone`
+   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

Original file line number	Diff line number	Diff line change
`@@ -1310,10 +1310,20 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {`
`1310`	`1310`	`return None;`
`1311`	`1311`	`}`
`1312`	`1312`	`}`
	`1313`	`+ if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative {`
	`1314`	`+ return None;`
	`1315`	`+ }`
`1313`	`1316`	`Some(imp)`
`1314`	`1317`	`})`
`1315`	`1318`	`.collect(),`
`1316`		`- None => all_impls.map(\|def_id\| self.tcx.impl_trait_ref(def_id).unwrap()).collect(),`
	`1319`	`+ None => all_impls`
	`1320`	`+ .filter_map(\|def_id\| {`
	`1321`	`+ if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative {`
	`1322`	`+ return None;`
	`1323`	`+ }`
	`1324`	`+ self.tcx.impl_trait_ref(def_id)`
	`1325`	`+ })`
	`1326`	`+ .collect(),`
`1317`	`1327`	`}`
`1318`	`1328`	`}`
`1319`	`1329`
Original file line number	Diff line number	Diff line change
`@@ -12,7 +12,6 @@ LL \| type U = str;`
`12`	`12`	`\|`
`13`	`13`	`= help: the following implementations were found:`
`14`	`14`	`<&T as Clone>`
`15`		`- <&mut T as Clone>`
`16`	`15`
`17`	`16`	`error: aborting due to previous error`
`18`	`17`
Original file line number	Diff line number	Diff line change
`@@ -12,7 +12,6 @@ LL \| fn f<'a, T: X<'a> + ?Sized>(x: &<T as X<'a>>::U) {`
`12`	`12`	`\|`
`13`	`13`	`= help: the following implementations were found:`
`14`	`14`	`<&T as Clone>`
`15`		`- <&mut T as Clone>`
`16`	`15`
`17`	`16`	`error: aborting due to previous error`
`18`	`17`
Original file line number	Diff line number	Diff line change
`@@ -12,7 +12,6 @@ LL \| type V = str;`
`12`	`12`	`\|`
`13`	`13`	`= help: the following implementations were found:`
`14`	`14`	`<&T as Clone>`
`15`		`- <&mut T as Clone>`
`16`	`15`
`17`	`16`	`error: aborting due to previous error`
`18`	`17`
Original file line number	Diff line number	Diff line change
`@@ -12,7 +12,6 @@ LL \| for<'b> <T as Z<'b, u16>>::W: Clone,`
`12`	`12`	`\|`
`13`	`13`	`= help: the following implementations were found:`
`14`	`14`	`<&T as Clone>`
`15`		`- <&mut T as Clone>`
`16`	`15`
`17`	`16`	error[E0277]: the trait bound `for<'b> <u16 as Z<'b, u16>>::W: Clone` is not satisfied
`18`	`17`	`--> $DIR/hr-associated-type-bound-param-2.rs:16:14`
`@@ -28,7 +27,6 @@ LL \| type W = str;`
`28`	`27`	`\|`
`29`	`28`	`= help: the following implementations were found:`
`30`	`29`	`<&T as Clone>`
`31`		`- <&mut T as Clone>`
`32`	`30`
`33`	`31`	error[E0277]: the trait bound `for<'b> <u16 as Z<'b, u16>>::W: Clone` is not satisfied
`34`	`32`	`--> $DIR/hr-associated-type-bound-param-2.rs:4:8`
`@@ -44,7 +42,6 @@ LL \| for<'b> <T as Z<'b, u16>>::W: Clone,`
`44`	`42`	`\|`
`45`	`43`	`= help: the following implementations were found:`
`46`	`44`	`<&T as Clone>`
`47`		`- <&mut T as Clone>`
`48`	`45`
`49`	`46`	`error: aborting due to 3 previous errors`
`50`	`47`
Original file line number	Diff line number	Diff line change
`@@ -10,8 +10,6 @@ LL \| async fn bar() {`
`10`	`10`	`LL \| is_qux(bar());`
`11`	`11`	\| ^^^^^^ within `impl Future`, the trait `Qux` is not implemented for `Foo`
`12`	`12`	`\|`
`13`		`- = help: the following implementations were found:`
`14`		`- <Foo as Qux>`
`15`	`13`	note: future does not implement `Qux` as this value is used across an await
`16`	`14`	`--> $DIR/issue-64130-3-other.rs:18:5`
`17`	`15`	`\|`