Add an experimental unsafe(force_target_feature) attribute.

This uses the feature gate for
https://github.com/rust-lang/rust/issues/143352, but is described in
https://github.com/rust-lang/rfcs/pull/3820 which is strongly tied to
the experiment.

3 files changed, 99 insertions, 0 deletions

diff --git a/tests/ui/feature-gates/feature-gate-effective-target-features.default.stderr b/tests/ui/feature-gates/feature-gate-effective-target-features.default.stderr
new file mode 100644
index 00000000000..34a56fe342e
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-effective-target-features.default.stderr
@@ -0,0 +1,37 @@
+error[E0658]: the `#[force_target_feature]` attribute is an experimental feature
+  --> $DIR/feature-gate-effective-target-features.rs:13:5
+   |
+LL |     #[unsafe(force_target_feature(enable = "avx2"))]
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #143352 <https://github.com/rust-lang/rust/issues/143352> for more information
+   = help: add `#![feature(effective_target_features)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: `#[target_feature(..)]` cannot be applied to safe trait method
+  --> $DIR/feature-gate-effective-target-features.rs:21:5
+   |
+LL |     #[target_feature(enable = "avx2")]
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot be applied to safe trait method
+LL |
+LL |     fn foo(&self) {}
+   |     ------------- not an `unsafe` function
+
+error[E0053]: method `foo` has an incompatible type for trait
+  --> $DIR/feature-gate-effective-target-features.rs:23:5
+   |
+LL |     fn foo(&self) {}
+   |     ^^^^^^^^^^^^^ expected safe fn, found unsafe fn
+   |
+note: type in trait
+  --> $DIR/feature-gate-effective-target-features.rs:7:5
+   |
+LL |     fn foo(&self);
+   |     ^^^^^^^^^^^^^^
+   = note: expected signature `fn(&Bar2)`
+              found signature `#[target_features] fn(&Bar2)`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0053, E0658.
+For more information about an error, try `rustc --explain E0053`.
diff --git a/tests/ui/feature-gates/feature-gate-effective-target-features.feature.stderr b/tests/ui/feature-gates/feature-gate-effective-target-features.feature.stderr
new file mode 100644
index 00000000000..d51956fa4d2
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-effective-target-features.feature.stderr
@@ -0,0 +1,35 @@
+warning: the feature `effective_target_features` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/feature-gate-effective-target-features.rs:3:30
+   |
+LL | #![cfg_attr(feature, feature(effective_target_features))]
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #143352 <https://github.com/rust-lang/rust/issues/143352> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error: `#[target_feature(..)]` cannot be applied to safe trait method
+  --> $DIR/feature-gate-effective-target-features.rs:21:5
+   |
+LL |     #[target_feature(enable = "avx2")]
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot be applied to safe trait method
+LL |
+LL |     fn foo(&self) {}
+   |     ------------- not an `unsafe` function
+
+error[E0053]: method `foo` has an incompatible type for trait
+  --> $DIR/feature-gate-effective-target-features.rs:23:5
+   |
+LL |     fn foo(&self) {}
+   |     ^^^^^^^^^^^^^ expected safe fn, found unsafe fn
+   |
+note: type in trait
+  --> $DIR/feature-gate-effective-target-features.rs:7:5
+   |
+LL |     fn foo(&self);
+   |     ^^^^^^^^^^^^^^
+   = note: expected signature `fn(&Bar2)`
+              found signature `#[target_features] fn(&Bar2)`
+
+error: aborting due to 2 previous errors; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0053`.
diff --git a/tests/ui/feature-gates/feature-gate-effective-target-features.rs b/tests/ui/feature-gates/feature-gate-effective-target-features.rs
new file mode 100644
index 00000000000..d383897e438
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-effective-target-features.rs
@@ -0,0 +1,27 @@
+//@ revisions: default feature
+//@ only-x86_64
+#![cfg_attr(feature, feature(effective_target_features))]
+//[feature]~^ WARN the feature `effective_target_features` is incomplete and may not be safe to use and/or cause compiler crashes
+
+trait Foo {
+    fn foo(&self);
+}
+
+struct Bar;
+
+impl Foo for Bar {
+    #[unsafe(force_target_feature(enable = "avx2"))]
+    //[default]~^ ERROR the `#[force_target_feature]` attribute is an experimental feature
+    fn foo(&self) {}
+}
+
+struct Bar2;
+
+impl Foo for Bar2 {
+    #[target_feature(enable = "avx2")]
+    //~^ ERROR `#[target_feature(..)]` cannot be applied to safe trait method
+    fn foo(&self) {}
+    //~^ ERROR method `foo` has an incompatible type for trait
+}
+
+fn main() {}