uninit/zeroed lint: warn against NULL vtables

Author: RalfJung

src/librustc_lint/builtin.rs

@@ -1949,6 +1949,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidValue {
                 Adt(..) if ty.is_box() => Some((format!("`Box` must be non-null"), None)),
                 FnPtr(..) => Some((format!("Function pointers must be non-null"), None)),
                 Never => Some((format!("The never type (`!`) has no valid value"), None)),
+                RawPtr(tm) if matches!(tm.ty.kind, Dynamic(..)) => // raw ptr to dyn Trait
+                    Some((format!("The vtable of a wide raw pointer must be non-null"), None)),
                 // Primitive types with other constraints.
                 Bool if init == InitKind::Uninit =>
                     Some((format!("Booleans must be `true` or `false`"), None)),

src/librustc_lint/lib.rs

@@ -15,6 +15,7 @@
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(nll)]
+#![feature(matches_macro)]
 
 #![recursion_limit="256"]
 

src/test/ui/lint/uninitialized-zeroed.rs

@@ -67,6 +67,9 @@ fn main() {
         let _val: NonNull<i32> = mem::zeroed(); //~ ERROR: does not permit zero-initialization
         let _val: NonNull<i32> = mem::uninitialized(); //~ ERROR: does not permit being left uninitialized
 
+        let _val: *const dyn Send = mem::zeroed(); //~ ERROR: does not permit zero-initialization
+        let _val: *const dyn Send = mem::uninitialized(); //~ ERROR: does not permit being left uninitialized
+
         // Things that can be zero, but not uninit.
         let _val: bool = mem::zeroed();
         let _val: bool = mem::uninitialized(); //~ ERROR: does not permit being left uninitialized

src/test/ui/lint/uninitialized-zeroed.stderr

@@ -307,8 +307,30 @@ LL |         let _val: NonNull<i32> = mem::uninitialized();
    |
    = note: std::ptr::NonNull<i32> must be non-null
 
+error: the type `*const dyn std::marker::Send` does not permit zero-initialization
+  --> $DIR/uninitialized-zeroed.rs:70:37
+   |
+LL |         let _val: *const dyn Send = mem::zeroed();
+   |                                     ^^^^^^^^^^^^^
+   |                                     |
+   |                                     this code causes undefined behavior when executed
+   |                                     help: use `MaybeUninit<T>` instead
+   |
+   = note: The vtable of a wide raw pointer must be non-null
+
+error: the type `*const dyn std::marker::Send` does not permit being left uninitialized
+  --> $DIR/uninitialized-zeroed.rs:71:37
+   |
+LL |         let _val: *const dyn Send = mem::uninitialized();
+   |                                     ^^^^^^^^^^^^^^^^^^^^
+   |                                     |
+   |                                     this code causes undefined behavior when executed
+   |                                     help: use `MaybeUninit<T>` instead
+   |
+   = note: The vtable of a wide raw pointer must be non-null
+
 error: the type `bool` does not permit being left uninitialized
-  --> $DIR/uninitialized-zeroed.rs:72:26
+  --> $DIR/uninitialized-zeroed.rs:75:26
    |
 LL |         let _val: bool = mem::uninitialized();
    |                          ^^^^^^^^^^^^^^^^^^^^
@@ -319,7 +341,7 @@ LL |         let _val: bool = mem::uninitialized();
    = note: Booleans must be `true` or `false`
 
 error: the type `Wrap<char>` does not permit being left uninitialized
-  --> $DIR/uninitialized-zeroed.rs:75:32
+  --> $DIR/uninitialized-zeroed.rs:78:32
    |
 LL |         let _val: Wrap<char> = mem::uninitialized();
    |                                ^^^^^^^^^^^^^^^^^^^^
@@ -334,7 +356,7 @@ LL | struct Wrap<T> { wrapped: T }
    |                  ^^^^^^^^^^
 
 error: the type `NonBig` does not permit being left uninitialized
-  --> $DIR/uninitialized-zeroed.rs:78:28
+  --> $DIR/uninitialized-zeroed.rs:81:28
    |
 LL |         let _val: NonBig = mem::uninitialized();
    |                            ^^^^^^^^^^^^^^^^^^^^
@@ -345,7 +367,7 @@ LL |         let _val: NonBig = mem::uninitialized();
    = note: NonBig must be initialized inside its custom valid range
 
 error: the type `&'static i32` does not permit zero-initialization
-  --> $DIR/uninitialized-zeroed.rs:81:34
+  --> $DIR/uninitialized-zeroed.rs:84:34
    |
 LL |         let _val: &'static i32 = mem::transmute(0usize);
    |                                  ^^^^^^^^^^^^^^^^^^^^^^
@@ -356,7 +378,7 @@ LL |         let _val: &'static i32 = mem::transmute(0usize);
    = note: References must be non-null
 
 error: the type `&'static [i32]` does not permit zero-initialization
-  --> $DIR/uninitialized-zeroed.rs:82:36
+  --> $DIR/uninitialized-zeroed.rs:85:36
    |
 LL |         let _val: &'static [i32] = mem::transmute((0usize, 0usize));
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -367,7 +389,7 @@ LL |         let _val: &'static [i32] = mem::transmute((0usize, 0usize));
    = note: References must be non-null
 
 error: the type `std::num::NonZeroU32` does not permit zero-initialization
-  --> $DIR/uninitialized-zeroed.rs:83:32
+  --> $DIR/uninitialized-zeroed.rs:86:32
    |
 LL |         let _val: NonZeroU32 = mem::transmute(0);
    |                                ^^^^^^^^^^^^^^^^^
@@ -377,5 +399,5 @@ LL |         let _val: NonZeroU32 = mem::transmute(0);
    |
    = note: std::num::NonZeroU32 must be non-null
 
-error: aborting due to 30 previous errors
+error: aborting due to 32 previous errors