Strengthen validation of FFI attributes

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -85,55 +85,11 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: DefId) -> CodegenFnAttrs {
         } else if attr.has_name(sym::rustc_allocator) {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR;
         } else if attr.has_name(sym::ffi_returns_twice) {
-            if tcx.is_foreign_item(did) {
-                codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE;
-            } else {
-                // `#[ffi_returns_twice]` is only allowed `extern fn`s.
-                struct_span_err!(
-                    tcx.sess,
-                    attr.span,
-                    E0724,
-                    "`#[ffi_returns_twice]` may only be used on foreign functions"
-                )
-                .emit();
-            }
+            codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_RETURNS_TWICE;
         } else if attr.has_name(sym::ffi_pure) {
-            if tcx.is_foreign_item(did) {
-                if attrs.iter().any(|a| a.has_name(sym::ffi_const)) {
-                    // `#[ffi_const]` functions cannot be `#[ffi_pure]`
-                    struct_span_err!(
-                        tcx.sess,
-                        attr.span,
-                        E0757,
-                        "`#[ffi_const]` function cannot be `#[ffi_pure]`"
-                    )
-                    .emit();
-                } else {
-                    codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_PURE;
-                }
-            } else {
-                // `#[ffi_pure]` is only allowed on foreign functions
-                struct_span_err!(
-                    tcx.sess,
-                    attr.span,
-                    E0755,
-                    "`#[ffi_pure]` may only be used on foreign functions"
-                )
-                .emit();
-            }
+            codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_PURE;
         } else if attr.has_name(sym::ffi_const) {
-            if tcx.is_foreign_item(did) {
-                codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_CONST;
-            } else {
-                // `#[ffi_const]` is only allowed on foreign functions
-                struct_span_err!(
-                    tcx.sess,
-                    attr.span,
-                    E0756,
-                    "`#[ffi_const]` may only be used on foreign functions"
-                )
-                .emit();
-            }
+            codegen_fn_attrs.flags |= CodegenFnAttrFlags::FFI_CONST;
         } else if attr.has_name(sym::rustc_nounwind) {
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
         } else if attr.has_name(sym::rustc_reallocator) {

compiler/rustc_error_messages/locales/en-US/passes.ftl

@@ -182,6 +182,18 @@ passes_has_incoherent_inherent_impl =
     `rustc_has_incoherent_inherent_impls` attribute should be applied to types or traits.
     .label = only adts, extern types and traits are supported
 
+passes_both_ffi_const_and_pure =
+    `#[ffi_const]` function cannot be `#[ffi_pure]`
+
+passes_ffi_pure_invalid_target =
+    `#[ffi_pure]` may only be used on foreign functions
+
+passes_ffi_const_invalid_target =
+    `#[ffi_const]` may only be used on foreign functions
+
+passes_ffi_returns_twice_invalid_target =
+    `#[ffi_returns_twice]` may only be used on foreign functions
+
 passes_must_use_async =
     `must_use` attribute on `async` functions applies to the anonymous `Future` returned by the function, not the value within
     .label = this attribute does nothing, the `Future`s returned by async functions are already `must_use`

compiler/rustc_passes/src/check_attr.rs

@@ -150,6 +150,9 @@ impl CheckAttrVisitor<'_> {
                 sym::rustc_has_incoherent_inherent_impls => {
                     self.check_has_incoherent_inherent_impls(&attr, span, target)
                 }
+                sym::ffi_pure => self.check_ffi_pure(attr.span, attrs, target),
+                sym::ffi_const => self.check_ffi_const(attr.span, target),
+                sym::ffi_returns_twice => self.check_ffi_returns_twice(attr.span, target),
                 sym::rustc_const_unstable
                 | sym::rustc_const_stable
                 | sym::unstable
@@ -1171,6 +1174,38 @@ impl CheckAttrVisitor<'_> {
         }
     }
 
+    fn check_ffi_pure(&self, attr_span: Span, attrs: &[Attribute], target: Target) -> bool {
+        if target != Target::ForeignFn {
+            self.tcx.sess.emit_err(errors::FfiPureInvalidTarget { attr_span });
+            return false;
+        }
+        if attrs.iter().any(|a| a.has_name(sym::ffi_const)) {
+            // `#[ffi_const]` functions cannot be `#[ffi_pure]`
+            self.tcx.sess.emit_err(errors::BothFfiConstAndPure { attr_span });
+            false
+        } else {
+            true
+        }
+    }
+
+    fn check_ffi_const(&self, attr_span: Span, target: Target) -> bool {
+        if target == Target::ForeignFn {
+            true
+        } else {
+            self.tcx.sess.emit_err(errors::FfiConstInvalidTarget { attr_span });
+            false
+        }
+    }
+
+    fn check_ffi_returns_twice(&self, attr_span: Span, target: Target) -> bool {
+        if target == Target::ForeignFn {
+            true
+        } else {
+            self.tcx.sess.emit_err(errors::FfiReturnsTwiceInvalidTarget { attr_span });
+            false
+        }
+    }
+
     /// Warns against some misuses of `#[must_use]`
     fn check_must_use(&self, hir_id: HirId, attr: &Attribute, target: Target) -> bool {
         if !matches!(

compiler/rustc_passes/src/errors.rs

@@ -347,6 +347,34 @@ pub struct HasIncoherentInherentImpl {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(passes_both_ffi_const_and_pure, code = "E0757")]
+pub struct BothFfiConstAndPure {
+    #[primary_span]
+    pub attr_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(passes_ffi_pure_invalid_target, code = "E0755")]
+pub struct FfiPureInvalidTarget {
+    #[primary_span]
+    pub attr_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(passes_ffi_const_invalid_target, code = "E0756")]
+pub struct FfiConstInvalidTarget {
+    #[primary_span]
+    pub attr_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(passes_ffi_returns_twice_invalid_target, code = "E0724")]
+pub struct FfiReturnsTwiceInvalidTarget {
+    #[primary_span]
+    pub attr_span: Span,
+}
+
 #[derive(LintDiagnostic)]
 #[diag(passes_must_use_async)]
 pub struct MustUseAsync {

tests/ui/ffi_const.rs

@@ -3,3 +3,13 @@
 
 #[ffi_const] //~ ERROR `#[ffi_const]` may only be used on foreign functions
 pub fn foo() {}
+
+#[ffi_const] //~ ERROR `#[ffi_const]` may only be used on foreign functions
+macro_rules! bar {
+    () => ()
+}
+
+extern "C" {
+    #[ffi_const] //~ ERROR `#[ffi_const]` may only be used on foreign functions
+    static INT: i32;
+}

tests/ui/ffi_const.stderr

@@ -4,6 +4,18 @@ error[E0756]: `#[ffi_const]` may only be used on foreign functions
 LL | #[ffi_const]
    | ^^^^^^^^^^^^
 
-error: aborting due to previous error
+error[E0756]: `#[ffi_const]` may only be used on foreign functions
+  --> $DIR/ffi_const.rs:7:1
+   |
+LL | #[ffi_const]
+   | ^^^^^^^^^^^^
+
+error[E0756]: `#[ffi_const]` may only be used on foreign functions
+  --> $DIR/ffi_const.rs:13:5
+   |
+LL |     #[ffi_const]
+   |     ^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0756`.

tests/ui/ffi_pure.rs

@@ -3,3 +3,13 @@
 
 #[ffi_pure] //~ ERROR `#[ffi_pure]` may only be used on foreign functions
 pub fn foo() {}
+
+#[ffi_pure] //~ ERROR `#[ffi_pure]` may only be used on foreign functions
+macro_rules! bar {
+    () => ()
+}
+
+extern "C" {
+    #[ffi_pure] //~ ERROR `#[ffi_pure]` may only be used on foreign functions
+    static INT: i32;
+}

tests/ui/ffi_pure.stderr

@@ -4,6 +4,18 @@ error[E0755]: `#[ffi_pure]` may only be used on foreign functions
 LL | #[ffi_pure]
    | ^^^^^^^^^^^
 
-error: aborting due to previous error
+error[E0755]: `#[ffi_pure]` may only be used on foreign functions
+  --> $DIR/ffi_pure.rs:7:1
+   |
+LL | #[ffi_pure]
+   | ^^^^^^^^^^^
+
+error[E0755]: `#[ffi_pure]` may only be used on foreign functions
+  --> $DIR/ffi_pure.rs:13:5
+   |
+LL |     #[ffi_pure]
+   |     ^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0755`.

tests/ui/ffi_returns_twice.rs

@@ -3,3 +3,13 @@
 
 #[ffi_returns_twice] //~ ERROR `#[ffi_returns_twice]` may only be used on foreign functions
 pub fn foo() {}
+
+#[ffi_returns_twice] //~ ERROR `#[ffi_returns_twice]` may only be used on foreign functions
+macro_rules! bar {
+    () => ()
+}
+
+extern "C" {
+    #[ffi_returns_twice] //~ ERROR `#[ffi_returns_twice]` may only be used on foreign functions
+    static INT: i32;
+}

tests/ui/ffi_returns_twice.stderr

@@ -4,6 +4,18 @@ error[E0724]: `#[ffi_returns_twice]` may only be used on foreign functions
 LL | #[ffi_returns_twice]
    | ^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to previous error
+error[E0724]: `#[ffi_returns_twice]` may only be used on foreign functions
+  --> $DIR/ffi_returns_twice.rs:7:1
+   |
+LL | #[ffi_returns_twice]
+   | ^^^^^^^^^^^^^^^^^^^^
+
+error[E0724]: `#[ffi_returns_twice]` may only be used on foreign functions
+  --> $DIR/ffi_returns_twice.rs:13:5
+   |
+LL |     #[ffi_returns_twice]
+   |     ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0724`.