Add tests for #[ffi_const] and #[ffi_pure] function attributes

Based on the work of gnzlbg <[email protected]>.

Author: neocturne

Diff for: src/test/codegen/ffi-const.rs

@@ -0,0 +1,12 @@
+// compile-flags: -C no-prepopulate-passes
+#![crate_type = "lib"]
+#![feature(ffi_const)]
+
+pub fn bar() { unsafe { foo() } }
+
+extern {
+    // CHECK-LABEL: declare void @foo()
+    // CHECK-SAME: [[ATTRS:#[0-9]+]]
+    // CHECK-DAG: attributes [[ATTRS]] = { {{.*}}readnone{{.*}} }
+    #[ffi_const] pub fn foo();
+}

Diff for: src/test/codegen/ffi-pure.rs

@@ -0,0 +1,12 @@
+// compile-flags: -C no-prepopulate-passes
+#![crate_type = "lib"]
+#![feature(ffi_pure)]
+
+pub fn bar() { unsafe { foo() } }
+
+extern {
+    // CHECK-LABEL: declare void @foo()
+    // CHECK-SAME: [[ATTRS:#[0-9]+]]
+    // CHECK-DAG: attributes [[ATTRS]] = { {{.*}}readonly{{.*}} }
+    #[ffi_pure] pub fn foo();
+}

Diff for: src/test/ui/feature-gates/feature-gate-ffi_const.rs

@@ -0,0 +1,6 @@
+#![crate_type = "lib"]
+
+extern {
+    #[ffi_const] //~ ERROR the `#[ffi_const]` attribute is an experimental feature
+    pub fn foo();
+}

Diff for: src/test/ui/feature-gates/feature-gate-ffi_const.stderr

@@ -0,0 +1,12 @@
+error[E0658]: the `#[ffi_const]` attribute is an experimental feature
+  --> $DIR/feature-gate-ffi_const.rs:4:5
+   |
+LL |     #[ffi_const]
+   |     ^^^^^^^^^^^^
+   |
+   = note: see issue #58328 <https://github.com/rust-lang/rust/issues/58328> for more information
+   = help: add `#![feature(ffi_const)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

Diff for: src/test/ui/feature-gates/feature-gate-ffi_pure.rs

@@ -0,0 +1,6 @@
+#![crate_type = "lib"]
+
+extern {
+    #[ffi_pure] //~ ERROR the `#[ffi_pure]` attribute is an experimental feature
+    pub fn foo();
+}

Diff for: src/test/ui/feature-gates/feature-gate-ffi_pure.stderr

@@ -0,0 +1,12 @@
+error[E0658]: the `#[ffi_pure]` attribute is an experimental feature
+  --> $DIR/feature-gate-ffi_pure.rs:4:5
+   |
+LL |     #[ffi_pure]
+   |     ^^^^^^^^^^^
+   |
+   = note: see issue #58329 <https://github.com/rust-lang/rust/issues/58329> for more information
+   = help: add `#![feature(ffi_pure)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

Diff for: src/test/ui/ffi_const.rs

@@ -0,0 +1,5 @@
+#![feature(ffi_const)]
+#![crate_type = "lib"]
+
+#[ffi_const] //~ ERROR `#[ffi_const]` may only be used on foreign functions
+pub fn foo() {}

Diff for: src/test/ui/ffi_const.stderr

@@ -0,0 +1,8 @@
+error[E0756]: `#[ffi_const]` may only be used on foreign functions
+  --> $DIR/ffi_const.rs:4:1
+   |
+LL | #[ffi_const]
+   | ^^^^^^^^^^^^
+
+error: aborting due to previous error
+

Diff for: src/test/ui/ffi_const2.rs

@@ -0,0 +1,11 @@
+#![feature(ffi_const, ffi_pure)]
+
+extern {
+    #[ffi_pure] //~ ERROR `#[ffi_const]` function cannot be `#[ffi_pure]`
+    #[ffi_const]
+    pub fn baz();
+}
+
+fn main() {
+    unsafe { baz() };
+}

Diff for: src/test/ui/ffi_const2.stderr

@@ -0,0 +1,8 @@
+error[E0757]: `#[ffi_const]` function cannot be `#[ffi_pure]`
+  --> $DIR/ffi_const2.rs:4:5
+   |
+LL |     #[ffi_pure]
+   |     ^^^^^^^^^^^
+
+error: aborting due to previous error
+

Diff for: src/test/ui/ffi_pure.rs

@@ -0,0 +1,5 @@
+#![feature(ffi_pure)]
+#![crate_type = "lib"]
+
+#[ffi_pure] //~ ERROR `#[ffi_pure]` may only be used on foreign functions
+pub fn foo() {}

Diff for: src/test/ui/ffi_pure.stderr

@@ -0,0 +1,8 @@
+error[E0755]: `#[ffi_pure]` may only be used on foreign functions
+  --> $DIR/ffi_pure.rs:4:1
+   |
+LL | #[ffi_pure]
+   | ^^^^^^^^^^^
+
+error: aborting due to previous error
+