Auto merge of #116930 - RalfJung:raw-ptr-match, r=<try>

patterns: reject raw pointers that are not just integers

Matching against `0 as *const i32` is fine, matching against `&42 as *const i32` is not.

Cc `@oli-obk` `@lcnr`

compiler/rustc_const_eval/src/const_eval/valtrees.rs

@@ -97,11 +97,27 @@ pub(crate) fn const_to_valtree_inner<'tcx>(
             Ok(ty::ValTree::Leaf(val.assert_int()))
         }
 
-        // Raw pointers are not allowed in type level constants, as we cannot properly test them for
-        // equality at compile-time (see `ptr_guaranteed_cmp`).
+        ty::RawPtr(_) => {
+            // Not all raw pointers are allowed, as we cannot properly test them for
+            // equality at compile-time (see `ptr_guaranteed_cmp`).
+            // However we allow those that are just integers in disguise.
+            // (We could allow wide raw pointers where both sides are integers in the future,
+            // but for now we reject them.)
+            let Ok(val) = ecx.read_scalar(place) else {
+                return Err(ValTreeCreationError::Other);
+            };
+            // We are in the CTFE machine, so ptr-to-int casts will fail.
+            // This can only be `Ok` if `val` already is an integer.
+            let Ok(val) = val.try_to_int() else {
+                return Err(ValTreeCreationError::Other);
+            };
+            // It's just a ScalarInt!
+            Ok(ty::ValTree::Leaf(val))
+        }
+
         // Technically we could allow function pointers (represented as `ty::Instance`), but this is not guaranteed to
         // agree with runtime equality tests.
-        ty::FnPtr(_) | ty::RawPtr(_) => Err(ValTreeCreationError::NonSupportedType),
+        ty::FnPtr(_) => Err(ValTreeCreationError::NonSupportedType),
 
         ty::Ref(_, _, _)  => {
             let Ok(derefd_place)= ecx.deref_pointer(place) else {
@@ -222,12 +238,14 @@ pub fn valtree_to_const_value<'tcx>(
             assert!(valtree.unwrap_branch().is_empty());
             mir::ConstValue::ZeroSized
         }
-        ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char => match valtree {
-            ty::ValTree::Leaf(scalar_int) => mir::ConstValue::Scalar(Scalar::Int(scalar_int)),
-            ty::ValTree::Branch(_) => bug!(
-                "ValTrees for Bool, Int, Uint, Float or Char should have the form ValTree::Leaf"
-            ),
-        },
+        ty::Bool | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Char | ty::RawPtr(_) => {
+            match valtree {
+                ty::ValTree::Leaf(scalar_int) => mir::ConstValue::Scalar(Scalar::Int(scalar_int)),
+                ty::ValTree::Branch(_) => bug!(
+                    "ValTrees for Bool, Int, Uint, Float, Char or RawPtr should have the form ValTree::Leaf"
+                ),
+            }
+        }
         ty::Ref(_, inner_ty, _) => {
             let mut ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, CanAccessStatics::No);
             let imm = valtree_to_ref(&mut ecx, valtree, *inner_ty);
@@ -281,7 +299,6 @@ pub fn valtree_to_const_value<'tcx>(
         | ty::Generator(..)
         | ty::GeneratorWitness(..)
         | ty::FnPtr(_)
-        | ty::RawPtr(_)
         | ty::Str
         | ty::Slice(_)
         | ty::Dynamic(..) => bug!("no ValTree should have been created for type {:?}", ty.kind()),

compiler/rustc_lint_defs/src/builtin.rs

@@ -2217,15 +2217,16 @@ declare_lint! {
     ///
     /// ### Explanation
     ///
-    /// Previous versions of Rust allowed function pointers and wide raw pointers in patterns.
+    /// Previous versions of Rust allowed function pointers and all raw pointers in patterns.
     /// While these work in many cases as expected by users, it is possible that due to
     /// optimizations pointers are "not equal to themselves" or pointers to different functions
     /// compare as equal during runtime. This is because LLVM optimizations can deduplicate
     /// functions if their bodies are the same, thus also making pointers to these functions point
     /// to the same location. Additionally functions may get duplicated if they are instantiated
-    /// in different crates and not deduplicated again via LTO.
+    /// in different crates and not deduplicated again via LTO. Pointer identity for memory
+    /// created by `const` is similarly unreliable.
     pub POINTER_STRUCTURAL_MATCH,
-    Allow,
+    Forbid,
     "pointers are not structural-match",
     @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,

compiler/rustc_mir_build/messages.ftl

@@ -242,7 +242,7 @@ mir_build_overlapping_range_endpoints = multiple patterns overlap on their endpo
 mir_build_pattern_not_covered = refutable pattern in {$origin}
     .pattern_ty = the matched value is of type `{$pattern_ty}`
 
-mir_build_pointer_pattern = function pointers and unsized pointers in patterns behave unpredictably and should not be relied upon. See https://github.com/rust-lang/rust/issues/70861 for details.
+mir_build_pointer_pattern = function pointers and raw pointers not derived from integers in patterns behave unpredictably and should not be relied upon. See https://github.com/rust-lang/rust/issues/70861 for details.
 
 mir_build_privately_uninhabited = pattern `{$witness_1}` is currently uninhabited, but this variant contains private fields which may become inhabited in the future
 

compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs

@@ -123,6 +123,8 @@ impl<'tcx> ConstToPat<'tcx> {
         });
         debug!(?check_body_for_struct_match_violation, ?mir_structural_match_violation);
 
+        let have_valtree =
+            matches!(cv, mir::Const::Ty(c) if matches!(c.kind(), ty::ConstKind::Value(_)));
         let inlined_const_as_pat = match cv {
             mir::Const::Ty(c) => match c.kind() {
                 ty::ConstKind::Param(_)
@@ -238,7 +240,9 @@ impl<'tcx> ConstToPat<'tcx> {
                 }
             } else if !self.saw_const_match_lint.get() {
                 match cv.ty().kind() {
-                    ty::RawPtr(pointee) if pointee.ty.is_sized(self.tcx(), self.param_env) => {}
+                    ty::RawPtr(..) if have_valtree => {
+                        // This is a good raw pointer, it was accepted by valtree construction.
+                    }
                     ty::FnPtr(..) | ty::RawPtr(..) => {
                         self.tcx().emit_spanned_lint(
                             lint::builtin::POINTER_STRUCTURAL_MATCH,
@@ -389,11 +393,19 @@ impl<'tcx> ConstToPat<'tcx> {
                 subpatterns: self
                     .field_pats(cv.unwrap_branch().iter().copied().zip(fields.iter()))?,
             },
-            ty::Adt(def, args) => PatKind::Leaf {
-                subpatterns: self.field_pats(cv.unwrap_branch().iter().copied().zip(
-                    def.non_enum_variant().fields.iter().map(|field| field.ty(self.tcx(), args)),
-                ))?,
-            },
+            ty::Adt(def, args) => {
+                assert!(!def.is_union()); // Valtree construction would never succeed for unions.
+                PatKind::Leaf {
+                    subpatterns: self.field_pats(
+                        cv.unwrap_branch().iter().copied().zip(
+                            def.non_enum_variant()
+                                .fields
+                                .iter()
+                                .map(|field| field.ty(self.tcx(), args)),
+                        ),
+                    )?,
+                }
+            }
             ty::Slice(elem_ty) => PatKind::Slice {
                 prefix: cv
                     .unwrap_branch()
@@ -480,10 +492,15 @@ impl<'tcx> ConstToPat<'tcx> {
                     }
                 }
             },
-            ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) => {
+            ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::RawPtr(..) => {
+                // The raw pointers we see here have been "vetted" by valtree construction to be
+                // just integers, so we simply allow them.
                 PatKind::Constant { value: mir::Const::Ty(ty::Const::new_value(tcx, cv, ty)) }
             }
-            ty::FnPtr(..) | ty::RawPtr(..) => unreachable!(),
+            ty::FnPtr(..) => {
+                // Valtree construction would never succeed for these, so this is unreachable.
+                unreachable!()
+            }
             _ => {
                 let err = InvalidPattern { span, non_sm_ty: ty };
                 let e = tcx.sess.emit_err(err);

tests/ui/consts/const_in_pattern/issue-44333.rs

@@ -16,9 +16,9 @@ const BAR: Func = bar;
 
 fn main() {
     match test(std::env::consts::ARCH.len()) {
-        FOO => println!("foo"), //~ WARN pointers in patterns behave unpredictably
+        FOO => println!("foo"), //~ WARN behave unpredictably
         //~^ WARN will become a hard error
-        BAR => println!("bar"), //~ WARN pointers in patterns behave unpredictably
+        BAR => println!("bar"), //~ WARN behave unpredictably
         //~^ WARN will become a hard error
         _ => unreachable!(),
     }

tests/ui/consts/const_in_pattern/issue-44333.stderr

@@ -1,4 +1,4 @@
-warning: function pointers and unsized pointers in patterns behave unpredictably and should not be relied upon. See https://github.com/rust-lang/rust/issues/70861 for details.
+warning: function pointers and raw pointers not derived from integers in patterns behave unpredictably and should not be relied upon. See https://github.com/rust-lang/rust/issues/70861 for details.
   --> $DIR/issue-44333.rs:19:9
    |
 LL |         FOO => println!("foo"),
@@ -12,7 +12,7 @@ note: the lint level is defined here
 LL | #![warn(pointer_structural_match)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^
 
-warning: function pointers and unsized pointers in patterns behave unpredictably and should not be relied upon. See https://github.com/rust-lang/rust/issues/70861 for details.
+warning: function pointers and raw pointers not derived from integers in patterns behave unpredictably and should not be relied upon. See https://github.com/rust-lang/rust/issues/70861 for details.
   --> $DIR/issue-44333.rs:21:9
    |
 LL |         BAR => println!("bar"),

tests/ui/consts/issue-34784.rs → tests/ui/consts/issue-34784-match-on-non-int-raw-ptr.rs

@@ -1,12 +1,11 @@
-// run-pass
-
-#![warn(pointer_structural_match)]
+#![deny(pointer_structural_match)]
 #![allow(dead_code)]
 const C: *const u8 = &0;
 
 fn foo(x: *const u8) {
     match x {
-        C => {}
+        C => {} //~ERROR: behave unpredictably
+        //~| previously accepted
         _ => {}
     }
 }
@@ -15,7 +14,8 @@ const D: *const [u8; 4] = b"abcd";
 
 fn main() {
     match D {
-        D => {}
+        D => {} //~ERROR: behave unpredictably
+        //~| previously accepted
         _ => {}
     }
 }

tests/ui/consts/issue-34784-match-on-non-int-raw-ptr.stderr

@@ -0,0 +1,25 @@
+error: function pointers and raw pointers not derived from integers in patterns behave unpredictably and should not be relied upon. See https://github.com/rust-lang/rust/issues/70861 for details.
+  --> $DIR/issue-34784-match-on-non-int-raw-ptr.rs:7:9
+   |
+LL |         C => {}
+   |         ^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #62411 <https://github.com/rust-lang/rust/issues/70861>
+note: the lint level is defined here
+  --> $DIR/issue-34784-match-on-non-int-raw-ptr.rs:1:9
+   |
+LL | #![deny(pointer_structural_match)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: function pointers and raw pointers not derived from integers in patterns behave unpredictably and should not be relied upon. See https://github.com/rust-lang/rust/issues/70861 for details.
+  --> $DIR/issue-34784-match-on-non-int-raw-ptr.rs:17:9
+   |
+LL |         D => {}
+   |         ^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #62411 <https://github.com/rust-lang/rust/issues/70861>
+
+error: aborting due to 2 previous errors
+

tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-63479-match-fnptr.rs

@@ -33,7 +33,7 @@ fn main() {
   let s = B(my_fn);
   match s {
     B(TEST) => println!("matched"),
-     //~^ WARN pointers in patterns behave unpredictably
+     //~^ WARN behave unpredictably
     //~| WARN this was previously accepted by the compiler but is being phased out
     _ => panic!("didn't match")
   };

tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/issue-63479-match-fnptr.stderr

@@ -1,4 +1,4 @@
-warning: function pointers and unsized pointers in patterns behave unpredictably and should not be relied upon. See https://github.com/rust-lang/rust/issues/70861 for details.
+warning: function pointers and raw pointers not derived from integers in patterns behave unpredictably and should not be relied upon. See https://github.com/rust-lang/rust/issues/70861 for details.
   --> $DIR/issue-63479-match-fnptr.rs:35:7
    |
 LL |     B(TEST) => println!("matched"),