resolve: prohibit foreign statics w/ generics

This commit modifies resolve to disallow foreign statics that use
parent generics.

`improper_ctypes` is not written to support type parameters, as these
are normally disallowed before the lint is run. Thus, type parameters in
foreign statics must be prohibited before the lint.

The only other case where this *could* have occured is in functions,
but typeck prohibits this with a "foreign items may not have type
parameters" error - a similar error did not exist for statics, because
statics cannot have type parameters, but they can use any
type parameters that are in scope (which isn't the case for functions).

Signed-off-by: David Wood <david@davidtw.co>

src/test/ui/inner-static-type-parameter.stderr

@@ -2,9 +2,7 @@ error[E0401]: can't use generic parameters from outer function
   --> $DIR/inner-static-type-parameter.rs:6:19
    |
 LL | fn foo<T>() {
-   |    --- - type parameter from outer function
-   |    |
-   |    try adding a local generic parameter in this method instead
+   |        - type parameter from outer function
 LL |     static a: Bar<T> = Bar::What;
    |                   ^ use of generic parameter from outer function
 

src/test/ui/resolve/issue-65025-extern-static-parent-generics.rs

@@ -0,0 +1,10 @@
+unsafe fn foo<A>() {
+    extern "C" {
+        static baz: *const A;
+        //~^ ERROR can't use generic parameters from outer function
+    }
+
+    let bar: *const u64 = core::mem::transmute(&baz);
+}
+
+fn main() { }

src/test/ui/resolve/issue-65025-extern-static-parent-generics.stderr

@@ -0,0 +1,12 @@
+error[E0401]: can't use generic parameters from outer function
+  --> $DIR/issue-65025-extern-static-parent-generics.rs:3:28
+   |
+LL | unsafe fn foo<A>() {
+   |               - type parameter from outer function
+LL |     extern "C" {
+LL |         static baz: *const A;
+   |                            ^ use of generic parameter from outer function
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0401`.

src/test/ui/resolve/issue-65035-static-with-parent-generics.rs

@@ -0,0 +1,29 @@
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+fn f<T>() {
+    extern "C" {
+        static a: *const T;
+        //~^ ERROR can't use generic parameters from outer function
+    }
+}
+
+fn g<T: Default>() {
+    static a: *const T = Default::default();
+    //~^ ERROR can't use generic parameters from outer function
+}
+
+fn h<const N: usize>() {
+    extern "C" {
+        static a: [u8; N];
+        //~^ ERROR can't use generic parameters from outer function
+    }
+}
+
+fn i<const N: usize>() {
+    static a: [u8; N] = [0; N];
+    //~^ ERROR can't use generic parameters from outer function
+    //~^^ ERROR can't use generic parameters from outer function
+}
+
+fn main() {}

src/test/ui/resolve/issue-65035-static-with-parent-generics.stderr

@@ -0,0 +1,53 @@
+error[E0401]: can't use generic parameters from outer function
+  --> $DIR/issue-65035-static-with-parent-generics.rs:6:26
+   |
+LL | fn f<T>() {
+   |      - type parameter from outer function
+LL |     extern "C" {
+LL |         static a: *const T;
+   |                          ^ use of generic parameter from outer function
+
+error[E0401]: can't use generic parameters from outer function
+  --> $DIR/issue-65035-static-with-parent-generics.rs:12:22
+   |
+LL | fn g<T: Default>() {
+   |      - type parameter from outer function
+LL |     static a: *const T = Default::default();
+   |                      ^ use of generic parameter from outer function
+
+error[E0401]: can't use generic parameters from outer function
+  --> $DIR/issue-65035-static-with-parent-generics.rs:18:24
+   |
+LL | fn h<const N: usize>() {
+   |            - const parameter from outer function
+LL |     extern "C" {
+LL |         static a: [u8; N];
+   |                        ^ use of generic parameter from outer function
+
+error[E0401]: can't use generic parameters from outer function
+  --> $DIR/issue-65035-static-with-parent-generics.rs:24:20
+   |
+LL | fn i<const N: usize>() {
+   |            - const parameter from outer function
+LL |     static a: [u8; N] = [0; N];
+   |                    ^ use of generic parameter from outer function
+
+error[E0401]: can't use generic parameters from outer function
+  --> $DIR/issue-65035-static-with-parent-generics.rs:24:29
+   |
+LL | fn i<const N: usize>() {
+   |            - const parameter from outer function
+LL |     static a: [u8; N] = [0; N];
+   |                             ^ use of generic parameter from outer function
+
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-65035-static-with-parent-generics.rs:1:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+
+error: aborting due to 5 previous errors
+
+For more information about this error, try `rustc --explain E0401`.