Rollup merge of #64809 - davidtwco:issue-64768-target-feature-const, r=varkor

hir: Disallow `target_feature` on constants

Fixes #64768.

This PR fixes an ICE when `#[target_feature]` is applied to constants by disallowing this with the same error as when `#[target_feature]` is applied to other places it shouldn't be.

I couldn't see anything in the [RFC](https://github.com/rust-lang/rfcs/blob/master/text/2045-target-feature.md) that suggested that `#[target_feature]` should be applicable to constants or any tests that suggested it should, though I might have missed something - if this is desirable in future, it remains possible to remove this error (but for the time being, I think this error is better than an ICE).

I also added some extra cases to the test for other places where `#[target_feature]` should not be permitted.

cc @gnzlbg

src/test/ui/attributes/multiple-invalid.rs

@@ -0,0 +1,10 @@
+// This test checks that all expected errors occur when there are multiple invalid attributes
+// on an item.
+
+#[inline]
+//~^ ERROR attribute should be applied to function or closure [E0518]
+#[target_feature(enable = "sse2")]
+//~^ ERROR attribute should be applied to a function
+const FOO: u8 = 0;
+
+fn main() { }

src/test/ui/attributes/multiple-invalid.stderr

@@ -0,0 +1,21 @@
+error[E0518]: attribute should be applied to function or closure
+  --> $DIR/multiple-invalid.rs:4:1
+   |
+LL | #[inline]
+   | ^^^^^^^^^
+...
+LL | const FOO: u8 = 0;
+   | ------------------ not a function or closure
+
+error: attribute should be applied to a function
+  --> $DIR/multiple-invalid.rs:6:1
+   |
+LL | #[target_feature(enable = "sse2")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |
+LL | const FOO: u8 = 0;
+   | ------------------ not a function
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0518`.

src/test/ui/target-feature-wrong.stderr

@@ -1,50 +0,0 @@
-error: malformed `target_feature` attribute input
-  --> $DIR/target-feature-wrong.rs:16:1
-   |
-LL | #[target_feature = "+sse2"]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: must be of the form: `#[target_feature(enable = "name")]`
-
-error: the feature named `foo` is not valid for this target
-  --> $DIR/target-feature-wrong.rs:18:18
-   |
-LL | #[target_feature(enable = "foo")]
-   |                  ^^^^^^^^^^^^^^ `foo` is not valid for this target
-
-error: malformed `target_feature` attribute input
-  --> $DIR/target-feature-wrong.rs:21:18
-   |
-LL | #[target_feature(bar)]
-   |                  ^^^ help: must be of the form: `enable = ".."`
-
-error: malformed `target_feature` attribute input
-  --> $DIR/target-feature-wrong.rs:23:18
-   |
-LL | #[target_feature(disable = "baz")]
-   |                  ^^^^^^^^^^^^^^^ help: must be of the form: `enable = ".."`
-
-error: `#[target_feature(..)]` can only be applied to `unsafe` functions
-  --> $DIR/target-feature-wrong.rs:27:1
-   |
-LL | #[target_feature(enable = "sse2")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can only be applied to `unsafe` functions
-...
-LL | fn bar() {}
-   | ----------- not an `unsafe` function
-
-error: attribute should be applied to a function
-  --> $DIR/target-feature-wrong.rs:33:1
-   |
-LL | #[target_feature(enable = "sse2")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-LL |
-LL | mod another {}
-   | -------------- not a function
-
-error: cannot use `#[inline(always)]` with `#[target_feature]`
-  --> $DIR/target-feature-wrong.rs:38:1
-   |
-LL | #[inline(always)]
-   | ^^^^^^^^^^^^^^^^^
-
-error: aborting due to 7 previous errors
-

src/test/ui/target-feature/gate.stderr

@@ -1,5 +1,5 @@
 error[E0658]: the target feature `avx512bw` is currently unstable
-  --> $DIR/target-feature-gate.rs:30:18
+  --> $DIR/gate.rs:30:18
    |
 LL | #[target_feature(enable = "avx512bw")]
    |                  ^^^^^^^^^^^^^^^^^^^

src/test/ui/target-feature/invalid-attribute.rs

@@ -35,6 +35,31 @@ fn bar() {}
 mod another {}
 //~^ NOTE not a function
 
+#[target_feature(enable = "sse2")]
+//~^ ERROR attribute should be applied to a function
+const FOO: usize = 7;
+//~^ NOTE not a function
+
+#[target_feature(enable = "sse2")]
+//~^ ERROR attribute should be applied to a function
+struct Foo;
+//~^ NOTE not a function
+
+#[target_feature(enable = "sse2")]
+//~^ ERROR attribute should be applied to a function
+enum Bar { }
+//~^ NOTE not a function
+
+#[target_feature(enable = "sse2")]
+//~^ ERROR attribute should be applied to a function
+union Qux { f1: u16, f2: u16 }
+//~^ NOTE not a function
+
+#[target_feature(enable = "sse2")]
+//~^ ERROR attribute should be applied to a function
+trait Baz { }
+//~^ NOTE not a function
+
 #[inline(always)]
 //~^ ERROR: cannot use `#[inline(always)]`
 #[target_feature(enable = "sse2")]

src/test/ui/target-feature/invalid-attribute.stderr

@@ -0,0 +1,95 @@
+error: malformed `target_feature` attribute input
+  --> $DIR/invalid-attribute.rs:16:1
+   |
+LL | #[target_feature = "+sse2"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: must be of the form: `#[target_feature(enable = "name")]`
+
+error: the feature named `foo` is not valid for this target
+  --> $DIR/invalid-attribute.rs:18:18
+   |
+LL | #[target_feature(enable = "foo")]
+   |                  ^^^^^^^^^^^^^^ `foo` is not valid for this target
+
+error: malformed `target_feature` attribute input
+  --> $DIR/invalid-attribute.rs:21:18
+   |
+LL | #[target_feature(bar)]
+   |                  ^^^ help: must be of the form: `enable = ".."`
+
+error: malformed `target_feature` attribute input
+  --> $DIR/invalid-attribute.rs:23:18
+   |
+LL | #[target_feature(disable = "baz")]
+   |                  ^^^^^^^^^^^^^^^ help: must be of the form: `enable = ".."`
+
+error: `#[target_feature(..)]` can only be applied to `unsafe` functions
+  --> $DIR/invalid-attribute.rs:27:1
+   |
+LL | #[target_feature(enable = "sse2")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can only be applied to `unsafe` functions
+...
+LL | fn bar() {}
+   | ----------- not an `unsafe` function
+
+error: attribute should be applied to a function
+  --> $DIR/invalid-attribute.rs:33:1
+   |
+LL | #[target_feature(enable = "sse2")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |
+LL | mod another {}
+   | -------------- not a function
+
+error: attribute should be applied to a function
+  --> $DIR/invalid-attribute.rs:38:1
+   |
+LL | #[target_feature(enable = "sse2")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |
+LL | const FOO: usize = 7;
+   | --------------------- not a function
+
+error: attribute should be applied to a function
+  --> $DIR/invalid-attribute.rs:43:1
+   |
+LL | #[target_feature(enable = "sse2")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |
+LL | struct Foo;
+   | ----------- not a function
+
+error: attribute should be applied to a function
+  --> $DIR/invalid-attribute.rs:48:1
+   |
+LL | #[target_feature(enable = "sse2")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |
+LL | enum Bar { }
+   | ------------ not a function
+
+error: attribute should be applied to a function
+  --> $DIR/invalid-attribute.rs:53:1
+   |
+LL | #[target_feature(enable = "sse2")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |
+LL | union Qux { f1: u16, f2: u16 }
+   | ------------------------------ not a function
+
+error: attribute should be applied to a function
+  --> $DIR/invalid-attribute.rs:58:1
+   |
+LL | #[target_feature(enable = "sse2")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |
+LL | trait Baz { }
+   | ------------- not a function
+
+error: cannot use `#[inline(always)]` with `#[target_feature]`
+  --> $DIR/invalid-attribute.rs:63:1
+   |
+LL | #[inline(always)]
+   | ^^^^^^^^^^^^^^^^^
+
+error: aborting due to 12 previous errors
+