From 90004f06d18f4658881230c675974cce0b631653 Mon Sep 17 00:00:00 2001
From: Camelid <camelidcamel@gmail.com>
Date: Fri, 8 Jan 2021 14:03:44 -0800
Subject: [PATCH] unsafeck: Don't treat AscribeUserType as use
Previously, if the MIR had an AscribeUserType statement that ascribed a
type to the pointee of a raw pointer, it would be treated as a dereference
of the raw pointer for purposes of unsafe-checking. For example, the
following code would be treated as containing a raw-pointer dereference:
fn foo(ptr: *const bool) {
let _: bool = *ptr;
}
Producing this error:
error[E0133]: dereference of raw pointer is unsafe and requires unsafe function or block
--> issue-80059.rs:2:12
|
2 | let _: bool = *ptr;
| ^^^^ dereference of raw pointer
Note that the error points to the type ascription as having a
dereference! That's because the generated AscribeUserType MIR statement
is treated as containing a dereference of `_1`:
AscribeUserType((*_1), +, UserTypeProjection { base: UserType(1), projs: [] });
Now the unsafe-checker ignores uses inside `AscribeUserType` statements,
which means this code now compiles successfully.
-----
Note that this code:
fn foo(ptr: *const bool) {
let _: bool = *ptr;
}
does *not* produce an error (it compiles fine) because of the magical
behavior of the `_` (wildcard) pattern (see #80059).
---
compiler/rustc_mir/src/transform/check_unsafety.rs | 9 ++++++++-
src/test/ui/unsafe/wildcard-type-ascription.rs | 7 +++++++
2 files changed, 15 insertions(+), 1 deletion(-)
create mode 100644 src/test/ui/unsafe/wildcard-type-ascription.rs
diff --git a/compiler/rustc_mir/src/transform/check_unsafety.rs b/compiler/rustc_mir/src/transform/check_unsafety.rs
index e64955c4986ce..4aa119e4da2e2 100644
--- a/compiler/rustc_mir/src/transform/check_unsafety.rs
+++ b/compiler/rustc_mir/src/transform/check_unsafety.rs
@@ -113,11 +113,18 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
| StatementKind::StorageLive(..)
| StatementKind::StorageDead(..)
| StatementKind::Retag { .. }
- | StatementKind::AscribeUserType(..)
| StatementKind::Coverage(..)
| StatementKind::Nop => {
// safe (at least as emitted during MIR construction)
}
+ StatementKind::AscribeUserType(..) => {
+ // safe (at least as emitted during MIR construction)
+ // This is handled separately because we don't want
+ // super_statement to be called.
+ // See this for more:
+ // https://github.com/rust-lang/rust/issues/80059#issuecomment-756968485
+ return;
+ }
StatementKind::LlvmInlineAsm { .. } => self.require_unsafe(
UnsafetyViolationKind::General,
diff --git a/src/test/ui/unsafe/wildcard-type-ascription.rs b/src/test/ui/unsafe/wildcard-type-ascription.rs
new file mode 100644
index 0000000000000..260d80a352ff9
--- /dev/null
+++ b/src/test/ui/unsafe/wildcard-type-ascription.rs
@@ -0,0 +1,7 @@
+// check-pass
+
+fn foo(ptr: *const bool) {
+ let _: bool = *ptr;
+}
+
+fn main() {}