check that entire ref is in-bounds before recursing; add macro for validation msgs on error

src/test/ui/consts/const-eval/ub-uninhabit.rs

@@ -9,14 +9,18 @@
 // except according to those terms.
 
 union Foo {
-    a: u8,
+    a: usize,
     b: Bar,
+    c: &'static Bar,
 }
 
 #[derive(Copy, Clone)]
 enum Bar {}
 
-const BAD_BAD_BAD: Bar = unsafe { Foo { a: 1 }.b};
+const BAD_BAD_BAD: Bar = unsafe { Foo { a: 1 }.b };
+//~^ ERROR this constant likely exhibits undefined behavior
+
+const BAD_BAD_REF: &Bar = unsafe { Foo { a: 1 }.c };
 //~^ ERROR this constant likely exhibits undefined behavior
 
 fn main() {

src/test/ui/consts/const-eval/ub-uninhabit.stderr

@@ -1,11 +1,19 @@
 error[E0080]: this constant likely exhibits undefined behavior
-  --> $DIR/ub-uninhabit.rs:19:1
+  --> $DIR/ub-uninhabit.rs:20:1
    |
-LL | const BAD_BAD_BAD: Bar = unsafe { Foo { a: 1 }.b};
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a value of an uninhabited type
+LL | const BAD_BAD_BAD: Bar = unsafe { Foo { a: 1 }.b };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a value of an uninhabited type
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
-error: aborting due to previous error
+error[E0080]: this constant likely exhibits undefined behavior
+  --> $DIR/ub-uninhabit.rs:23:1
+   |
+LL | const BAD_BAD_REF: &Bar = unsafe { Foo { a: 1 }.c };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a value of an uninhabited type at .<deref>
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0080`.

src/test/ui/consts/const-eval/ub-usize-in-ref.rs

@@ -8,15 +8,13 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-pass
-
 union Foo {
     a: &'static u8,
     b: usize,
 }
 
-// This might point to an invalid address, but that's the user's problem
 const USIZE_AS_STATIC_REF: &'static u8 = unsafe { Foo { b: 1337 }.a};
+//~^ ERROR this constant likely exhibits undefined behavior
 
 fn main() {
 }

src/test/ui/consts/const-eval/ub-usize-in-ref.stderr

@@ -0,0 +1,11 @@
+error[E0080]: this constant likely exhibits undefined behavior
+  --> $DIR/ub-usize-in-ref.rs:16:1
+   |
+LL | const USIZE_AS_STATIC_REF: &'static u8 = unsafe { Foo { b: 1337 }.a};
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered integer pointer in non-ZST reference
+   |
+   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.

src/test/ui/union-ub-fat-ptr.stderr

@@ -2,7 +2,7 @@ error[E0080]: this constant likely exhibits undefined behavior
   --> $DIR/union-ub-fat-ptr.rs:87:1
    |
 LL | const B: &str = unsafe { SliceTransmute { repr: SliceRepr { ptr: &42, len: 999 } }.str};
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized or out-of-bounds memory at .<deref>
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling reference (not entirely in bounds)
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
@@ -26,7 +26,7 @@ error[E0080]: this constant likely exhibits undefined behavior
   --> $DIR/union-ub-fat-ptr.rs:99:1
    |
 LL | const B2: &[u8] = unsafe { SliceTransmute { repr: SliceRepr { ptr: &42, len: 999 } }.slice};
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized or out-of-bounds memory at .<deref>[1]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered dangling reference (not entirely in bounds)
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
@@ -42,7 +42,7 @@ error[E0080]: this constant likely exhibits undefined behavior
   --> $DIR/union-ub-fat-ptr.rs:106:1
    |
 LL | const D: &Trait = unsafe { DynTransmute { repr: DynRepr { ptr: &92, vtable: &3 } }.rust};
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered invalid vtable in fat pointer at .<deref>
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered invalid drop fn in vtable
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
@@ -50,7 +50,7 @@ error[E0080]: this constant likely exhibits undefined behavior
   --> $DIR/union-ub-fat-ptr.rs:109:1
    |
 LL | const E: &Trait = unsafe { DynTransmute { repr2: DynRepr2 { ptr: &92, vtable: &3 } }.rust};
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered invalid vtable in fat pointer at .<deref>
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered invalid drop fn in vtable
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
@@ -98,7 +98,7 @@ error[E0080]: this constant likely exhibits undefined behavior
   --> $DIR/union-ub-fat-ptr.rs:132:1
    |
 LL | const J1: &str = unsafe { SliceTransmute { slice: &[0xFF] }.str };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered non-UTF-8 data in str at .<deref>
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized or non-UTF-8 data in str at .<deref>
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
 
@@ -106,7 +106,7 @@ error[E0080]: this constant likely exhibits undefined behavior
   --> $DIR/union-ub-fat-ptr.rs:135:1
    |
 LL | const J2: &MyStr = unsafe { SliceTransmute { slice: &[0xFF] }.my_str };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered non-UTF-8 data in str at .<deref>.0
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized or non-UTF-8 data 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 rust compiler repository if you believe it should not be considered undefined behavior