Structurally resolve before checking ! in HIR typeck

compiler/rustc_hir_typeck/src/expr.rs

@@ -68,7 +68,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // While we don't allow *arbitrary* coercions here, we *do* allow
         // coercions from ! to `expected`.
-        if ty.is_never() && self.expr_guaranteed_to_constitute_read_for_never(expr) {
+        if self.try_structurally_resolve_type(expr.span, ty).is_never()
+            && self.expr_guaranteed_to_constitute_read_for_never(expr)
+        {
             if let Some(_) = self.typeck_results.borrow().adjustments().get(expr.hir_id) {
                 let reported = self.dcx().span_delayed_bug(
                     expr.span,
@@ -274,7 +276,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // unless it's a place expression that isn't being read from, in which case
         // diverging would be unsound since we may never actually read the `!`.
         // e.g. `let _ = *never_ptr;` with `never_ptr: *const !`.
-        if ty.is_never() && self.expr_guaranteed_to_constitute_read_for_never(expr) {
+        if self.try_structurally_resolve_type(expr.span, ty).is_never()
+            && self.expr_guaranteed_to_constitute_read_for_never(expr)
+        {
             self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
         }
 

tests/ui/associated-consts/associated-const-type-parameter-arrays-2.rs

@@ -15,6 +15,7 @@ impl Foo for Def {
 pub fn test<A: Foo, B: Foo>() {
     let _array = [4; <A as Foo>::Y];
     //~^ ERROR constant expression depends on a generic parameter
+    //~| ERROR constant expression depends on a generic parameter
 }
 
 fn main() {

tests/ui/associated-consts/associated-const-type-parameter-arrays-2.stderr

@@ -6,5 +6,13 @@ LL |     let _array = [4; <A as Foo>::Y];
    |
    = note: this may fail depending on what value the parameter takes
 
-error: aborting due to 1 previous error
+error: constant expression depends on a generic parameter
+  --> $DIR/associated-const-type-parameter-arrays-2.rs:16:18
+   |
+LL |     let _array = [4; <A as Foo>::Y];
+   |                  ^^^^^^^^^^^^^^^^^^
+   |
+   = note: this may fail depending on what value the parameter takes
+
+error: aborting due to 2 previous errors
 

tests/ui/const-generics/const-arg-in-const-arg.min.stderr

@@ -53,7 +53,7 @@ LL |     let _: [u8; baz::<'b>(&())];
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:26:23
+  --> $DIR/const-arg-in-const-arg.rs:27:23
    |
 LL |     let _ = [0; bar::<N>()];
    |                       ^ cannot perform const operation using `N`
@@ -62,7 +62,7 @@ LL |     let _ = [0; bar::<N>()];
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:28:23
+  --> $DIR/const-arg-in-const-arg.rs:29:23
    |
 LL |     let _ = [0; faz::<'a>(&())];
    |                       ^^ cannot perform const operation using `'a`
@@ -71,7 +71,7 @@ LL |     let _ = [0; faz::<'a>(&())];
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:30:23
+  --> $DIR/const-arg-in-const-arg.rs:31:23
    |
 LL |     let _ = [0; baz::<'a>(&())];
    |                       ^^ cannot perform const operation using `'a`
@@ -80,7 +80,7 @@ LL |     let _ = [0; baz::<'a>(&())];
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:31:23
+  --> $DIR/const-arg-in-const-arg.rs:32:23
    |
 LL |     let _ = [0; faz::<'b>(&())];
    |                       ^^ cannot perform const operation using `'b`
@@ -89,7 +89,7 @@ LL |     let _ = [0; faz::<'b>(&())];
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:33:23
+  --> $DIR/const-arg-in-const-arg.rs:34:23
    |
 LL |     let _ = [0; baz::<'b>(&())];
    |                       ^^ cannot perform const operation using `'b`
@@ -98,7 +98,7 @@ LL |     let _ = [0; baz::<'b>(&())];
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:34:24
+  --> $DIR/const-arg-in-const-arg.rs:35:24
    |
 LL |     let _: Foo<{ foo::<T>() }>;
    |                        ^ cannot perform const operation using `T`
@@ -107,7 +107,7 @@ LL |     let _: Foo<{ foo::<T>() }>;
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:35:24
+  --> $DIR/const-arg-in-const-arg.rs:36:24
    |
 LL |     let _: Foo<{ bar::<N>() }>;
    |                        ^ cannot perform const operation using `N`
@@ -116,7 +116,7 @@ LL |     let _: Foo<{ bar::<N>() }>;
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:37:24
+  --> $DIR/const-arg-in-const-arg.rs:38:24
    |
 LL |     let _: Foo<{ faz::<'a>(&()) }>;
    |                        ^^ cannot perform const operation using `'a`
@@ -125,7 +125,7 @@ LL |     let _: Foo<{ faz::<'a>(&()) }>;
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:39:24
+  --> $DIR/const-arg-in-const-arg.rs:40:24
    |
 LL |     let _: Foo<{ baz::<'a>(&()) }>;
    |                        ^^ cannot perform const operation using `'a`
@@ -134,7 +134,7 @@ LL |     let _: Foo<{ baz::<'a>(&()) }>;
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:40:24
+  --> $DIR/const-arg-in-const-arg.rs:41:24
    |
 LL |     let _: Foo<{ faz::<'b>(&()) }>;
    |                        ^^ cannot perform const operation using `'b`
@@ -143,7 +143,7 @@ LL |     let _: Foo<{ faz::<'b>(&()) }>;
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:42:24
+  --> $DIR/const-arg-in-const-arg.rs:43:24
    |
 LL |     let _: Foo<{ baz::<'b>(&()) }>;
    |                        ^^ cannot perform const operation using `'b`
@@ -152,7 +152,7 @@ LL |     let _: Foo<{ baz::<'b>(&()) }>;
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:43:27
+  --> $DIR/const-arg-in-const-arg.rs:44:27
    |
 LL |     let _ = Foo::<{ foo::<T>() }>;
    |                           ^ cannot perform const operation using `T`
@@ -161,7 +161,7 @@ LL |     let _ = Foo::<{ foo::<T>() }>;
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:44:27
+  --> $DIR/const-arg-in-const-arg.rs:45:27
    |
 LL |     let _ = Foo::<{ bar::<N>() }>;
    |                           ^ cannot perform const operation using `N`
@@ -170,7 +170,7 @@ LL |     let _ = Foo::<{ bar::<N>() }>;
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:46:27
+  --> $DIR/const-arg-in-const-arg.rs:47:27
    |
 LL |     let _ = Foo::<{ faz::<'a>(&()) }>;
    |                           ^^ cannot perform const operation using `'a`
@@ -179,7 +179,7 @@ LL |     let _ = Foo::<{ faz::<'a>(&()) }>;
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:48:27
+  --> $DIR/const-arg-in-const-arg.rs:49:27
    |
 LL |     let _ = Foo::<{ baz::<'a>(&()) }>;
    |                           ^^ cannot perform const operation using `'a`
@@ -188,7 +188,7 @@ LL |     let _ = Foo::<{ baz::<'a>(&()) }>;
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:49:27
+  --> $DIR/const-arg-in-const-arg.rs:50:27
    |
 LL |     let _ = Foo::<{ faz::<'b>(&()) }>;
    |                           ^^ cannot perform const operation using `'b`
@@ -197,7 +197,7 @@ LL |     let _ = Foo::<{ faz::<'b>(&()) }>;
    = help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
 
 error: generic parameters may not be used in const operations
-  --> $DIR/const-arg-in-const-arg.rs:51:27
+  --> $DIR/const-arg-in-const-arg.rs:52:27
    |
 LL |     let _ = Foo::<{ baz::<'b>(&()) }>;
    |                           ^^ cannot perform const operation using `'b`
@@ -241,7 +241,7 @@ LL | const fn faz<'a>(_: &'a ()) -> usize { 13 }
    |              ^^
 
 error[E0747]: unresolved item provided when a constant was expected
-  --> $DIR/const-arg-in-const-arg.rs:35:24
+  --> $DIR/const-arg-in-const-arg.rs:36:24
    |
 LL |     let _: Foo<{ bar::<N>() }>;
    |                        ^
@@ -252,7 +252,7 @@ LL |     let _: Foo<{ bar::<{ N }>() }>;
    |                        +   +
 
 error[E0794]: cannot specify lifetime arguments explicitly if late bound lifetime parameters are present
-  --> $DIR/const-arg-in-const-arg.rs:37:24
+  --> $DIR/const-arg-in-const-arg.rs:38:24
    |
 LL |     let _: Foo<{ faz::<'a>(&()) }>;
    |                        ^^
@@ -264,7 +264,7 @@ LL | const fn faz<'a>(_: &'a ()) -> usize { 13 }
    |              ^^
 
 error[E0794]: cannot specify lifetime arguments explicitly if late bound lifetime parameters are present
-  --> $DIR/const-arg-in-const-arg.rs:40:24
+  --> $DIR/const-arg-in-const-arg.rs:41:24
    |
 LL |     let _: Foo<{ faz::<'b>(&()) }>;
    |                        ^^
@@ -283,8 +283,16 @@ LL |     let _ = [0; foo::<T>()];
    |
    = note: this may fail depending on what value the parameter takes
 
+error: constant expression depends on a generic parameter
+  --> $DIR/const-arg-in-const-arg.rs:25:13
+   |
+LL |     let _ = [0; foo::<T>()];
+   |             ^^^^^^^^^^^^^^^
+   |
+   = note: this may fail depending on what value the parameter takes
+
 error[E0747]: unresolved item provided when a constant was expected
-  --> $DIR/const-arg-in-const-arg.rs:26:23
+  --> $DIR/const-arg-in-const-arg.rs:27:23
    |
 LL |     let _ = [0; bar::<N>()];
    |                       ^
@@ -295,7 +303,7 @@ LL |     let _ = [0; bar::<{ N }>()];
    |                       +   +
 
 error[E0794]: cannot specify lifetime arguments explicitly if late bound lifetime parameters are present
-  --> $DIR/const-arg-in-const-arg.rs:28:23
+  --> $DIR/const-arg-in-const-arg.rs:29:23
    |
 LL |     let _ = [0; faz::<'a>(&())];
    |                       ^^
@@ -307,7 +315,7 @@ LL | const fn faz<'a>(_: &'a ()) -> usize { 13 }
    |              ^^
 
 error[E0794]: cannot specify lifetime arguments explicitly if late bound lifetime parameters are present
-  --> $DIR/const-arg-in-const-arg.rs:31:23
+  --> $DIR/const-arg-in-const-arg.rs:32:23
    |
 LL |     let _ = [0; faz::<'b>(&())];
    |                       ^^
@@ -319,7 +327,7 @@ LL | const fn faz<'a>(_: &'a ()) -> usize { 13 }
    |              ^^
 
 error[E0747]: unresolved item provided when a constant was expected
-  --> $DIR/const-arg-in-const-arg.rs:44:27
+  --> $DIR/const-arg-in-const-arg.rs:45:27
    |
 LL |     let _ = Foo::<{ bar::<N>() }>;
    |                           ^
@@ -330,7 +338,7 @@ LL |     let _ = Foo::<{ bar::<{ N }>() }>;
    |                           +   +
 
 error[E0794]: cannot specify lifetime arguments explicitly if late bound lifetime parameters are present
-  --> $DIR/const-arg-in-const-arg.rs:46:27
+  --> $DIR/const-arg-in-const-arg.rs:47:27
    |
 LL |     let _ = Foo::<{ faz::<'a>(&()) }>;
    |                           ^^
@@ -342,7 +350,7 @@ LL | const fn faz<'a>(_: &'a ()) -> usize { 13 }
    |              ^^
 
 error[E0794]: cannot specify lifetime arguments explicitly if late bound lifetime parameters are present
-  --> $DIR/const-arg-in-const-arg.rs:49:27
+  --> $DIR/const-arg-in-const-arg.rs:50:27
    |
 LL |     let _ = Foo::<{ faz::<'b>(&()) }>;
    |                           ^^
@@ -353,7 +361,7 @@ note: the late bound lifetime parameter is introduced here
 LL | const fn faz<'a>(_: &'a ()) -> usize { 13 }
    |              ^^
 
-error: aborting due to 36 previous errors
+error: aborting due to 37 previous errors
 
 Some errors have detailed explanations: E0747, E0794.
 For more information about an error, try `rustc --explain E0747`.

tests/ui/const-generics/const-arg-in-const-arg.rs

@@ -23,6 +23,7 @@ fn test<'a, 'b, T, const N: usize>() where &'b (): Sized {
     let _: [u8; baz::<'b>(&())]; //[min]~ ERROR generic parameters may not
 
     let _ = [0; foo::<T>()]; //[min]~ ERROR constant expression depends on a generic parameter
+                             //[min]~^ ERROR constant expression depends on a generic parameter
     let _ = [0; bar::<N>()]; //[min]~ ERROR generic parameters may not
                              //[min]~^ ERROR unresolved item provided when a constant was expected
     let _ = [0; faz::<'a>(&())]; //[min]~ ERROR generic parameters may not

tests/ui/const-generics/generic_const_exprs/dependence_lint.gce.stderr

@@ -1,11 +1,3 @@
-error: overly complex generic constant
-  --> $DIR/dependence_lint.rs:17:9
-   |
-LL |     [0; if false { size_of::<T>() } else { 3 }]; // lint on stable, error with gce
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ control flow is not supported in generic constants
-   |
-   = help: consider moving this anonymous constant into a `const` function
-
 error: overly complex generic constant
   --> $DIR/dependence_lint.rs:21:17
    |
@@ -36,5 +28,13 @@ help: try adding a `where` bound
 LL | fn foo<T>() where [(); size_of::<*mut T>()]: {
    |             ++++++++++++++++++++++++++++++++
 
+error: overly complex generic constant
+  --> $DIR/dependence_lint.rs:17:9
+   |
+LL |     [0; if false { size_of::<T>() } else { 3 }]; // lint on stable, error with gce
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ control flow is not supported in generic constants
+   |
+   = help: consider moving this anonymous constant into a `const` function
+
 error: aborting due to 4 previous errors
 

tests/ui/consts/too_generic_eval_ice.rs

@@ -7,6 +7,7 @@ impl<A, B> Foo<A, B> {
         [5; Self::HOST_SIZE] == [6; 0]
         //~^ ERROR constant expression depends on a generic parameter
         //~| ERROR constant expression depends on a generic parameter
+        //~| ERROR constant expression depends on a generic parameter
         //~| ERROR can't compare `[{integer}; Self::HOST_SIZE]` with `[{integer}; 0]`
     }
 }

tests/ui/consts/too_generic_eval_ice.stderr

@@ -6,6 +6,14 @@ LL |         [5; Self::HOST_SIZE] == [6; 0]
    |
    = note: this may fail depending on what value the parameter takes
 
+error: constant expression depends on a generic parameter
+  --> $DIR/too_generic_eval_ice.rs:7:9
+   |
+LL |         [5; Self::HOST_SIZE] == [6; 0]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this may fail depending on what value the parameter takes
+
 error: constant expression depends on a generic parameter
   --> $DIR/too_generic_eval_ice.rs:7:30
    |
@@ -32,6 +40,6 @@ LL |         [5; Self::HOST_SIZE] == [6; 0]
              `[T; N]` implements `PartialEq<[U]>`
            and 3 others
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

tests/ui/error-codes/E0746.stderr

@@ -19,8 +19,11 @@ error[E0746]: return type cannot have an unboxed trait object
 LL | fn bar() -> dyn Trait {
    |             ^^^^^^^^^ doesn't have a size known at compile-time
    |
-   = help: if there were a single returned type, you could use `impl Trait` instead
-help: box the return type, and wrap all of the returned values in `Box::new`
+help: consider returning an `impl Trait` instead of a `dyn Trait`
+   |
+LL | fn bar() -> impl Trait {
+   |             ~~~~
+help: alternatively, box the return type, and wrap all of the returned values in `Box::new`
    |
 LL ~ fn bar() -> Box<dyn Trait> {
 LL |     if true {