Ignore AscribeUserType in unsafeck to avoid duplicate diagnostics.

Author: cjgillot

compiler/rustc_mir_transform/src/check_unsafety.rs

@@ -100,14 +100,16 @@ impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
             | StatementKind::StorageLive(..)
             | StatementKind::StorageDead(..)
             | StatementKind::Retag { .. }
-            | StatementKind::AscribeUserType(..)
             | StatementKind::PlaceMention(..)
             | StatementKind::Coverage(..)
             | StatementKind::Intrinsic(..)
             | StatementKind::ConstEvalCounter
             | StatementKind::Nop => {
                 // safe (at least as emitted during MIR construction)
             }
+            // `AscribeUserType` just exists to help MIR borrowck.  It has no semantics, and
+            // everything is already reported by `PlaceMention`.
+            StatementKind::AscribeUserType(..) => return,
         }
         self.super_statement(statement, location);
     }

tests/ui/binding/issue-53114-safety-checks.rs

@@ -36,7 +36,6 @@ fn let_ascribe_gets_unsafe_field() {
     let p = P { a: &2, b: &3 };
     let _: _ = &p.b;  //~ ERROR    reference to packed field
     let _: _ = u1.a;  //~ ERROR  [E0133]
-                      //~^ ERROR  [E0133]
     let _: _ = &u2.a; //~ ERROR  [E0133]
 
     // variation on above with `_` in substructure

tests/ui/binding/issue-53114-safety-checks.stderr

@@ -26,7 +26,7 @@ LL |     let _: _ = &p.b;
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/issue-53114-safety-checks.rs:43:20
+  --> $DIR/issue-53114-safety-checks.rs:42:20
    |
 LL |     let (_,): _ = (&p.b,);
    |                    ^^^^
@@ -35,7 +35,7 @@ LL |     let (_,): _ = (&p.b,);
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/issue-53114-safety-checks.rs:52:11
+  --> $DIR/issue-53114-safety-checks.rs:51:11
    |
 LL |     match &p.b  { _ => { } }
    |           ^^^^
@@ -44,7 +44,7 @@ LL |     match &p.b  { _ => { } }
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/issue-53114-safety-checks.rs:57:12
+  --> $DIR/issue-53114-safety-checks.rs:56:12
    |
 LL |     match (&p.b,)  { (_,) => { } }
    |            ^^^^
@@ -93,70 +93,62 @@ LL |     let _: _ = u1.a;
    = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
 
 error[E0133]: access to union field is unsafe and requires unsafe function or block
-  --> $DIR/issue-53114-safety-checks.rs:38:12
-   |
-LL |     let _: _ = u1.a;
-   |            ^ access to union field
-   |
-   = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
-
-error[E0133]: access to union field is unsafe and requires unsafe function or block
-  --> $DIR/issue-53114-safety-checks.rs:40:16
+  --> $DIR/issue-53114-safety-checks.rs:39:16
    |
 LL |     let _: _ = &u2.a;
    |                ^^^^^ access to union field
    |
    = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
 
 error[E0133]: access to union field is unsafe and requires unsafe function or block
-  --> $DIR/issue-53114-safety-checks.rs:44:20
+  --> $DIR/issue-53114-safety-checks.rs:43:20
    |
 LL |     let (_,): _ = (u1.a,);
    |                    ^^^^ access to union field
    |
    = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
 
 error[E0133]: access to union field is unsafe and requires unsafe function or block
-  --> $DIR/issue-53114-safety-checks.rs:45:20
+  --> $DIR/issue-53114-safety-checks.rs:44:20
    |
 LL |     let (_,): _ = (&u2.a,);
    |                    ^^^^^ access to union field
    |
    = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
 
 error[E0133]: access to union field is unsafe and requires unsafe function or block
-  --> $DIR/issue-53114-safety-checks.rs:53:11
+  --> $DIR/issue-53114-safety-checks.rs:52:11
    |
 LL |     match u1.a  { _ => { } }
    |           ^^^^ access to union field
    |
    = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
 
 error[E0133]: access to union field is unsafe and requires unsafe function or block
-  --> $DIR/issue-53114-safety-checks.rs:54:11
+  --> $DIR/issue-53114-safety-checks.rs:53:11
    |
 LL |     match &u2.a { _ => { } }
    |           ^^^^^ access to union field
    |
    = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
 
 error[E0133]: access to union field is unsafe and requires unsafe function or block
-  --> $DIR/issue-53114-safety-checks.rs:58:12
+  --> $DIR/issue-53114-safety-checks.rs:57:12
    |
 LL |     match (u1.a,)  { (_,) => { } }
    |            ^^^^ access to union field
    |
    = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
 
 error[E0133]: access to union field is unsafe and requires unsafe function or block
-  --> $DIR/issue-53114-safety-checks.rs:59:12
+  --> $DIR/issue-53114-safety-checks.rs:58:12
    |
 LL |     match (&u2.a,) { (_,) => { } }
    |            ^^^^^ access to union field
    |
    = note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
 
-error: aborting due to 19 previous errors
+error: aborting due to 18 previous errors
 
 Some errors have detailed explanations: E0133, E0793.
 For more information about an error, try `rustc --explain E0133`.

tests/ui/unsafe/unsafe-fn-deref-ptr.mir.stderr

@@ -15,21 +15,13 @@ LL |     let _: u8 = *p;
    = note: raw pointers may be null, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
 
 error[E0133]: dereference of raw pointer is unsafe and requires unsafe function or block
-  --> $DIR/unsafe-fn-deref-ptr.rs:6:12
-   |
-LL |     let _: u8 = *p;
-   |            ^^ dereference of raw pointer
-   |
-   = note: raw pointers may be null, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
-
-error[E0133]: dereference of raw pointer is unsafe and requires unsafe function or block
-  --> $DIR/unsafe-fn-deref-ptr.rs:8:12
+  --> $DIR/unsafe-fn-deref-ptr.rs:7:12
    |
 LL |     return *p;
    |            ^^ dereference of raw pointer
    |
    = note: raw pointers may be null, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0133`.

tests/ui/unsafe/unsafe-fn-deref-ptr.rs

@@ -4,7 +4,6 @@
 fn f(p: *const u8) -> u8 {
     let _ = *p; //~ ERROR dereference of raw pointer is unsafe
     let _: u8 = *p; //~ ERROR dereference of raw pointer is unsafe
-                    //[mir]~^ ERROR dereference of raw pointer is unsafe
     return *p; //~ ERROR dereference of raw pointer is unsafe
 }
 

tests/ui/unsafe/unsafe-fn-deref-ptr.thir.stderr

@@ -15,7 +15,7 @@ LL |     let _: u8 = *p;
    = note: raw pointers may be null, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
 
 error[E0133]: dereference of raw pointer is unsafe and requires unsafe function or block
-  --> $DIR/unsafe-fn-deref-ptr.rs:8:12
+  --> $DIR/unsafe-fn-deref-ptr.rs:7:12
    |
 LL |     return *p;
    |            ^^ dereference of raw pointer