also identiy MaybeUninit::uninit().assume_init() as dangerous

Author: RalfJung

src/librustc/lint/context.rs

@@ -699,6 +699,9 @@ impl<'a, 'tcx> LateContext<'a, 'tcx> {
 
     /// Check if a `DefId`'s path matches the given absolute type path usage.
     ///
+    /// Anonymous scopes such as `extern` imports are matched with `kw::Invalid`;
+    /// inherent `impl` blocks are matched with the name of the type.
+    ///
     /// # Examples
     ///
     /// ```rust,ignore (no context or def id available)

src/librustc_lint/builtin.rs

@@ -1911,8 +1911,13 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidValue {
             // `Invalid` represents the empty string and matches that.
             const TRANSMUTE_PATH: &[Symbol] =
                 &[sym::core, sym::intrinsics, kw::Invalid, sym::transmute];
+            const MU_ZEROED_PATH: &[Symbol] =
+                &[sym::core, sym::mem, sym::maybe_uninit, sym::MaybeUninit, sym::zeroed];
+            const MU_UNINIT_PATH: &[Symbol] =
+                &[sym::core, sym::mem, sym::maybe_uninit, sym::MaybeUninit, sym::uninit];
 
             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
+                // Find calls to `mem::{uninitialized,zeroed}` methods.
                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
                     let def_id = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
 
@@ -1927,8 +1932,22 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidValue {
                             return Some(InitKind::Zeroed);
                         }
                     }
-                    // FIXME: Also detect `MaybeUninit::zeroed().assume_init()` and
-                    // `MaybeUninit::uninit().assume_init()`.
+                }
+            } else if let hir::ExprKind::MethodCall(ref path, _, ref args) = expr.kind {
+                // Find problematic calls to `MaybeUninit::assume_init`.
+                if path.ident.name == sym::assume_init {
+                    // This is a call to *some* method named `assume_init`.
+                    // See if the `self` parameter is one of the dangerous constructors.
+                    if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
+                        if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
+                            let def_id = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
+                            if cx.match_def_path(def_id, MU_ZEROED_PATH) {
+                                return Some(InitKind::Zeroed);
+                            } else if cx.match_def_path(def_id, MU_UNINIT_PATH) {
+                                return Some(InitKind::Uninit);
+                            }
+                        }
+                    }
                 }
             }
 

src/libsyntax_pos/symbol.rs

@@ -148,6 +148,7 @@ symbols! {
         associated_type_bounds,
         associated_type_defaults,
         associated_types,
+        assume_init,
         async_await,
         async_closure,
         attr,
@@ -417,6 +418,8 @@ symbols! {
         match_beginning_vert,
         match_default_bindings,
         may_dangle,
+        maybe_uninit,
+        MaybeUninit,
         mem,
         member_constraints,
         message,
@@ -709,6 +712,7 @@ symbols! {
         underscore_imports,
         underscore_lifetimes,
         uniform_paths,
+        uninit,
         uninitialized,
         universal_impl_trait,
         unmarked_api,

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

@@ -85,10 +85,16 @@ fn main() {
         let _val: &'static [i32] = mem::transmute((0usize, 0usize)); //~ ERROR: does not permit zero-initialization
         let _val: NonZeroU32 = mem::transmute(0); //~ ERROR: does not permit zero-initialization
 
+        // `MaybeUninit` cases
+        let _val: NonNull<i32> = MaybeUninit::zeroed().assume_init(); //~ ERROR: does not permit zero-initialization
+        let _val: NonNull<i32> = MaybeUninit::uninit().assume_init(); //~ ERROR: does not permit being left uninitialized
+        let _val: bool = MaybeUninit::uninit().assume_init(); //~ ERROR: does not permit being left uninitialized
+
         // Some more types that should work just fine.
         let _val: Option<&'static i32> = mem::zeroed();
         let _val: Option<fn()> = mem::zeroed();
         let _val: MaybeUninit<&'static i32> = mem::zeroed();
         let _val: i32 = mem::zeroed();
+        let _val: bool = MaybeUninit::zeroed().assume_init();
     }
 }

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

@@ -399,5 +399,38 @@ LL |         let _val: NonZeroU32 = mem::transmute(0);
    |
    = note: std::num::NonZeroU32 must be non-null
 
-error: aborting due to 32 previous errors
+error: the type `std::ptr::NonNull<i32>` does not permit zero-initialization
+  --> $DIR/uninitialized-zeroed.rs:89:34
+   |
+LL |         let _val: NonNull<i32> = MaybeUninit::zeroed().assume_init();
+   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                  |
+   |                                  this code causes undefined behavior when executed
+   |                                  help: use `MaybeUninit<T>` instead
+   |
+   = note: std::ptr::NonNull<i32> must be non-null
+
+error: the type `std::ptr::NonNull<i32>` does not permit being left uninitialized
+  --> $DIR/uninitialized-zeroed.rs:90:34
+   |
+LL |         let _val: NonNull<i32> = MaybeUninit::uninit().assume_init();
+   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                  |
+   |                                  this code causes undefined behavior when executed
+   |                                  help: use `MaybeUninit<T>` instead
+   |
+   = note: std::ptr::NonNull<i32> must be non-null
+
+error: the type `bool` does not permit being left uninitialized
+  --> $DIR/uninitialized-zeroed.rs:91:26
+   |
+LL |         let _val: bool = MaybeUninit::uninit().assume_init();
+   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                          |
+   |                          this code causes undefined behavior when executed
+   |                          help: use `MaybeUninit<T>` instead
+   |
+   = note: Booleans must be `true` or `false`
+
+error: aborting due to 35 previous errors