Implement check_attr

Author: tiif

compiler/rustc_passes/messages.ftl

@@ -594,6 +594,10 @@ passes_rustc_allow_const_fn_unstable =
     attribute should be applied to `const fn`
     .label = not a `const fn`
 
+passes_rustc_unstable_feature_bound = 
+    attribute should be applied to `impl` or free function outside of any `impl` or trait 
+    .label = not an `impl` or free function 
+
 passes_rustc_const_stable_indirect_pairing =
     `const_stable_indirect` attribute does not make sense on `rustc_const_stable` function, its behavior is already implied
 passes_rustc_dirty_clean =

compiler/rustc_passes/src/check_attr.rs

@@ -142,8 +142,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 }
                 Attribute::Parsed(AttributeKind::Repr(_)) => { /* handled below this loop and elsewhere */
                 }
-                Attribute::Parsed(AttributeKind::AllowUnstableFeature(_)) => {
-                    // FIXME: handle this later.
+                Attribute::Parsed(AttributeKind::AllowUnstableFeature(syms)) => {
+                    self.check_unstable_feature_bound(syms.first().unwrap().1, span, target)
                 }
                 Attribute::Parsed(
                     AttributeKind::BodyStability { .. }
@@ -2277,6 +2277,47 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
+    fn check_unstable_feature_bound(&self, attr_span: Span, span: Span, target: Target) {
+        match target {
+            Target::Fn | Target::Impl => {}
+            Target::ExternCrate |
+            Target::Use |
+            Target::Static |
+            Target::Const |
+            Target::Closure |
+            Target::Mod |
+            Target::ForeignMod |
+            Target::GlobalAsm |
+            Target::TyAlias |
+            Target::Enum |
+            Target::Variant |
+            Target::Struct |
+            Target::Field |
+            Target::Union |
+            Target::Trait |
+            Target::TraitAlias |
+            Target::Expression |
+            Target::Statement |
+            Target::Arm |
+            Target::AssocConst |
+            Target::Method(_) |
+            Target::AssocTy |
+            Target::ForeignFn |
+            Target::ForeignStatic |
+            Target::ForeignTy |
+            Target::GenericParam(_) |
+            Target::MacroDef |
+            Target::Param |
+            Target::PatField |
+            Target::ExprField |
+            Target::WherePredicate => {
+                self.tcx
+                    .dcx()
+                    .emit_err(errors::RustcUnstableFeatureBound{ attr_span, span });
+            }
+        }
+    }
+
     fn check_rustc_std_internal_symbol(&self, attr: &Attribute, span: Span, target: Target) {
         match target {
             Target::Fn | Target::Static | Target::ForeignFn | Target::ForeignStatic => {}

compiler/rustc_passes/src/errors.rs

@@ -662,6 +662,16 @@ pub(crate) struct RustcAllowConstFnUnstable {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(passes_rustc_unstable_feature_bound)]
+pub(crate) struct RustcUnstableFeatureBound {
+    #[primary_span]
+    pub attr_span: Span,
+    #[label]
+    pub span: Span,
+}
+
+
 #[derive(Diagnostic)]
 #[diag(passes_rustc_std_internal_symbol)]
 pub(crate) struct RustcStdInternalSymbol {