Check arg/ret sizedness at ExprKind::Path.

src/librustc_typeck/check/mod.rs

@@ -3956,6 +3956,31 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                     tcx.types.err
                 };
 
+                if let ty::FnDef(..) = ty.sty {
+                    let fn_sig = ty.fn_sig(tcx);
+                    if !tcx.features().unsized_locals {
+                        // We want to remove some Sized bounds from std functions,
+                        // but don't want to expose the removal to stable Rust.
+                        // i.e. we don't want to allow
+                        //
+                        // ```rust
+                        // drop as fn(str);
+                        // ```
+                        //
+                        // to work in stable even if the Sized bound on `drop` is relaxed.
+                        for i in 0..fn_sig.inputs().skip_binder().len() {
+                            let input = tcx.erase_late_bound_regions(&fn_sig.input(i));
+                            self.require_type_is_sized_deferred(input, expr.span,
+                                                                traits::SizedArgumentType);
+                        }
+                    }
+                    // Here we want to prevent struct constructors from returning unsized types.
+                    // There were two cases this happened: fn pointer coercion in stable
+                    // and usual function call in presense of unsized_locals.
+                    let output = tcx.erase_late_bound_regions(&fn_sig.output());
+                    self.require_type_is_sized_deferred(output, expr.span, traits::SizedReturnType);
+                }
+
                 // We always require that the type provided as the value for
                 // a type parameter outlives the moment of instantiation.
                 let substs = self.tables.borrow().node_substs(expr.hir_id);

src/test/ui/issues/issue-30355.nll.stderr

@@ -1,22 +0,0 @@
-error[E0161]: cannot move a value of type X: the size of X cannot be statically determined
-  --> $DIR/issue-30355.rs:15:6
-   |
-LL |     &X(*Y)
-   |      ^^^^^
-
-error[E0161]: cannot move a value of type [u8]: the size of [u8] cannot be statically determined
-  --> $DIR/issue-30355.rs:15:8
-   |
-LL |     &X(*Y)
-   |        ^^
-
-error[E0508]: cannot move out of type `[u8]`, a non-copy slice
-  --> $DIR/issue-30355.rs:15:8
-   |
-LL |     &X(*Y)
-   |        ^^ cannot move out of here
-
-error: aborting due to 3 previous errors
-
-Some errors occurred: E0161, E0508.
-For more information about an error, try `rustc --explain E0161`.

src/test/ui/issues/issue-30355.rs

@@ -13,9 +13,7 @@ pub struct X([u8]);
 pub static Y: &'static X = {
     const Y: &'static [u8] = b"";
     &X(*Y)
-    //~^ ERROR cannot move out
-    //~^^ ERROR cannot move a
-    //~^^^ ERROR cannot move a
+    //~^ ERROR E0277
 };
 
 fn main() {}

src/test/ui/issues/issue-30355.stderr

@@ -1,22 +1,14 @@
-error[E0161]: cannot move a value of type X: the size of X cannot be statically determined
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
   --> $DIR/issue-30355.rs:15:6
    |
 LL |     &X(*Y)
-   |      ^^^^^
-
-error[E0161]: cannot move a value of type [u8]: the size of [u8] cannot be statically determined
-  --> $DIR/issue-30355.rs:15:8
+   |      ^ doesn't have a size known at compile-time
    |
-LL |     &X(*Y)
-   |        ^^
+   = help: the trait `std::marker::Sized` is not implemented for `[u8]`
+   = note: to learn more, visit <https://doc.rust-lang.org/book/second-edition/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+   = note: all function arguments must have a statically known size
+   = help: unsized locals are gated as an unstable feature
 
-error[E0507]: cannot move out of borrowed content
-  --> $DIR/issue-30355.rs:15:8
-   |
-LL |     &X(*Y)
-   |        ^^ cannot move out of borrowed content
+error: aborting due to previous error
 
-error: aborting due to 3 previous errors
-
-Some errors occurred: E0161, E0507.
-For more information about an error, try `rustc --explain E0161`.
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/unsized-locals/unsized-exprs.rs

@@ -23,4 +23,6 @@ fn main() {
     //~^ERROR E0277
     udrop::<A<[u8]>>(A { 0: *foo() });
     //~^ERROR E0277
+    udrop::<A<[u8]>>(A(*foo()));
+    //~^ERROR E0277
 }

src/test/ui/unsized-locals/unsized-exprs.stderr

@@ -20,6 +20,17 @@ LL |     udrop::<A<[u8]>>(A { 0: *foo() });
    = note: required because it appears within the type `A<[u8]>`
    = note: structs must have a statically known size to be initialized
 
-error: aborting due to 2 previous errors
+error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
+  --> $DIR/unsized-exprs.rs:26:22
+   |
+LL |     udrop::<A<[u8]>>(A(*foo()));
+   |                      ^ doesn't have a size known at compile-time
+   |
+   = help: within `A<[u8]>`, the trait `std::marker::Sized` is not implemented for `[u8]`
+   = note: to learn more, visit <https://doc.rust-lang.org/book/second-edition/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+   = note: required because it appears within the type `A<[u8]>`
+   = note: the return type of a function must have a statically known size
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

src/test/ui/unsized-locals/unsized-exprs2.rs

@@ -21,6 +21,4 @@ impl std::ops::Add<i32> for A<[u8]> {
 fn main() {
     udrop::<[u8]>(foo()[..]);
     //~^ERROR cannot move out of indexed content
-    // FIXME: should be error
-    udrop::<A<[u8]>>(A(*foo()));
 }