Auto merge of #85332 - RalfJung:ptr-in-str, r=oli-obk

CTFE validation: handle pointers in str

I also finally learned how I can match *some* NOTEs in a ui test without matching all of them, and applied that to some const tests in the 2nd commit where I added NOTE because I did not know what I was doing. I can separate this into its own PR if you prefer.

Fixes #83182
r? `@oli-obk`

Author: bors

compiler/rustc_mir/src/interpret/validity.rs

@@ -833,6 +833,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
                     self.ecx.memory.read_bytes(mplace.ptr, Size::from_bytes(len)),
                     self.path,
                     err_ub!(InvalidUninitBytes(..)) => { "uninitialized data in `str`" },
+                    err_unsup!(ReadPointerAsBytes) => { "a pointer in `str`" },
                 );
             }
             ty::Array(tys, ..) | ty::Slice(tys)

src/test/ui/consts/const-eval/dangling.rs

@@ -3,13 +3,11 @@
 use std::mem;
 
 // Make sure we error with the right kind of error on a too large slice.
-const TEST: () = { unsafe { //~ NOTE
+const TEST: () = { unsafe {
     let slice: *const [u8] = mem::transmute((1usize, usize::MAX));
     let _val = &*slice; //~ ERROR: any use of this value will cause an error
-    //~| NOTE: slice is bigger than largest supported object
-    //~| on by default
+    //~| slice is bigger than largest supported object
     //~| WARN this was previously accepted by the compiler but is being phased out
-    //~| NOTE
 } };
 
 fn main() {}

src/test/ui/consts/const-eval/dangling.stderr

@@ -6,7 +6,6 @@ LL | |     let slice: *const [u8] = mem::transmute((1usize, usize::MAX));
 LL | |     let _val = &*slice;
    | |                ^^^^^^^ invalid metadata in wide pointer: slice is bigger than largest supported object
 LL | |
-...  |
 LL | |
 LL | | } };
    | |____-

src/test/ui/consts/const-points-to-static.rs

@@ -5,9 +5,7 @@
 
 const TEST: &u8 = &MY_STATIC;
 //~^ ERROR it is undefined behavior to use this value
-//~| NOTE  encountered a reference pointing to a static variable
-//~| NOTE undefined behavior
-//~| NOTE the raw bytes of the constant
+//~| encountered a reference pointing to a static variable
 
 static MY_STATIC: u8 = 4;
 

src/test/ui/consts/issue-83182.32bit.stderr

@@ -0,0 +1,14 @@
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/issue-83182.rs:5:1
+   |
+LL | const MYSTR_NO_INIT: &MyStr = unsafe { mem::transmute::<&[_], _>(&[&()]) };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer in `str` at .<deref>.0
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
+   = note: the raw bytes of the constant (size: 8, align: 4) {
+               ╾─alloc3──╼ 01 00 00 00                         │ ╾──╼....
+           }
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.

src/test/ui/consts/issue-83182.64bit.stderr

@@ -0,0 +1,14 @@
+error[E0080]: it is undefined behavior to use this value
+  --> $DIR/issue-83182.rs:5:1
+   |
+LL | const MYSTR_NO_INIT: &MyStr = unsafe { mem::transmute::<&[_], _>(&[&()]) };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer in `str` at .<deref>.0
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
+   = note: the raw bytes of the constant (size: 16, align: 8) {
+               ╾───────alloc3────────╼ 01 00 00 00 00 00 00 00 │ ╾──────╼........
+           }
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.

src/test/ui/consts/issue-83182.rs

@@ -0,0 +1,8 @@
+// stderr-per-bitwidth
+
+use std::mem;
+struct MyStr(str);
+const MYSTR_NO_INIT: &MyStr = unsafe { mem::transmute::<&[_], _>(&[&()]) };
+//~^ ERROR: it is undefined behavior to use this value
+//~| type validation failed: encountered a pointer in `str`
+fn main() {}

src/test/ui/consts/miri_unleashed/const_refers_to_static2.32bit.stderr

@@ -3,8 +3,6 @@ error[E0080]: it is undefined behavior to use this value
    |
 LL | / const REF_INTERIOR_MUT: &usize = {
 LL | |
-LL | |
-LL | |
 LL | |     static FOO: AtomicUsize = AtomicUsize::new(0);
 LL | |     unsafe { &*(&FOO as *const _ as *const usize) }
 LL | | };
@@ -16,12 +14,10 @@ LL | | };
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const_refers_to_static2.rs:20:1
+  --> $DIR/const_refers_to_static2.rs:18:1
    |
 LL | / const READ_IMMUT: &usize = {
 LL | |
-LL | |
-LL | |
 LL | |     static FOO: usize = 0;
 LL | |     &FOO
 LL | | };
@@ -35,17 +31,17 @@ LL | | };
 warning: skipping const checks
    |
 help: skipping check that does not even have a feature gate
-  --> $DIR/const_refers_to_static2.rs:16:18
+  --> $DIR/const_refers_to_static2.rs:14:18
    |
 LL |     unsafe { &*(&FOO as *const _ as *const usize) }
    |                  ^^^
 help: skipping check for `const_raw_ptr_deref` feature
-  --> $DIR/const_refers_to_static2.rs:16:14
+  --> $DIR/const_refers_to_static2.rs:14:14
    |
 LL |     unsafe { &*(&FOO as *const _ as *const usize) }
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/const_refers_to_static2.rs:25:6
+  --> $DIR/const_refers_to_static2.rs:21:6
    |
 LL |     &FOO
    |      ^^^

src/test/ui/consts/miri_unleashed/const_refers_to_static2.64bit.stderr

@@ -3,8 +3,6 @@ error[E0080]: it is undefined behavior to use this value
    |
 LL | / const REF_INTERIOR_MUT: &usize = {
 LL | |
-LL | |
-LL | |
 LL | |     static FOO: AtomicUsize = AtomicUsize::new(0);
 LL | |     unsafe { &*(&FOO as *const _ as *const usize) }
 LL | | };
@@ -16,12 +14,10 @@ LL | | };
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/const_refers_to_static2.rs:20:1
+  --> $DIR/const_refers_to_static2.rs:18:1
    |
 LL | / const READ_IMMUT: &usize = {
 LL | |
-LL | |
-LL | |
 LL | |     static FOO: usize = 0;
 LL | |     &FOO
 LL | | };
@@ -35,17 +31,17 @@ LL | | };
 warning: skipping const checks
    |
 help: skipping check that does not even have a feature gate
-  --> $DIR/const_refers_to_static2.rs:16:18
+  --> $DIR/const_refers_to_static2.rs:14:18
    |
 LL |     unsafe { &*(&FOO as *const _ as *const usize) }
    |                  ^^^
 help: skipping check for `const_raw_ptr_deref` feature
-  --> $DIR/const_refers_to_static2.rs:16:14
+  --> $DIR/const_refers_to_static2.rs:14:14
    |
 LL |     unsafe { &*(&FOO as *const _ as *const usize) }
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/const_refers_to_static2.rs:25:6
+  --> $DIR/const_refers_to_static2.rs:21:6
    |
 LL |     &FOO
    |      ^^^

src/test/ui/consts/miri_unleashed/const_refers_to_static2.rs

@@ -9,18 +9,14 @@ use std::sync::atomic::Ordering;
 // so they cause an immediate error when *defining* the const.
 
 const REF_INTERIOR_MUT: &usize = { //~ ERROR undefined behavior to use this value
-//~| NOTE encountered a reference pointing to a static variable
-//~| NOTE undefined behavior
-//~| NOTE the raw bytes of the constant
+//~| encountered a reference pointing to a static variable
     static FOO: AtomicUsize = AtomicUsize::new(0);
     unsafe { &*(&FOO as *const _ as *const usize) }
 };
 
 // ok some day perhaps
 const READ_IMMUT: &usize = { //~ ERROR it is undefined behavior to use this value
-//~| NOTE encountered a reference pointing to a static variable
-//~| NOTE undefined behavior
-//~| NOTE the raw bytes of the constant
+//~| encountered a reference pointing to a static variable
     static FOO: usize = 0;
     &FOO
 };