Gate tool_attributes feature

Author: topecongiro

src/libsyntax/attr.rs

@@ -108,6 +108,12 @@ pub fn is_known(attr: &Attribute) -> bool {
     })
 }
 
+const RUST_KNOWN_TOOL: &[&str] = &["clippy", "rustfmt"];
+
+pub fn is_known_tool(attr: &Attribute) -> bool {
+    RUST_KNOWN_TOOL.contains(&attr.name().as_str().as_ref())
+}
+
 impl NestedMetaItem {
     /// Returns the MetaItem if self is a NestedMetaItemKind::MetaItem.
     pub fn meta_item(&self) -> Option<&MetaItem> {
@@ -251,6 +257,10 @@ impl Attribute {
     pub fn is_value_str(&self) -> bool {
         self.value_str().is_some()
     }
+
+    pub fn is_scoped(&self) -> bool {
+        self.path.segments.len() > 1
+    }
 }
 
 impl MetaItem {

src/libsyntax/diagnostic_list.rs

@@ -366,4 +366,5 @@ register_diagnostics! {
     E0589, // invalid `repr(align)` attribute
     E0629, // missing 'feature' (rustc_const_unstable)
     E0630, // rustc_const_unstable attribute must be paired with stable/unstable attribute
+    E0693, // an unknown tool name found in scoped attributes
 }

src/libsyntax/ext/expand.rs

@@ -857,12 +857,16 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
     fn check_attributes(&mut self, attrs: &[ast::Attribute]) {
         let features = self.cx.ecfg.features.unwrap();
         for attr in attrs.iter() {
-            feature_gate::check_attribute(attr, self.cx.parse_sess, features);
+            self.check_attribute_inner(attr, features);
         }
     }
 
     fn check_attribute(&mut self, at: &ast::Attribute) {
         let features = self.cx.ecfg.features.unwrap();
+        self.check_attribute_inner(at, features);
+    }
+
+    fn check_attribute_inner(&mut self, at: &ast::Attribute, features: &Features) {
         feature_gate::check_attribute(at, self.cx.parse_sess, features);
     }
 }

src/libsyntax/feature_gate.rs

@@ -449,6 +449,9 @@ declare_features! (
 
     // Use `?` as the Kleene "at most one" operator
     (active, macro_at_most_once_rep, "1.25.0", Some(48075)),
+
+    // Scoped attributes
+    (active, tool_attributes, "1.25.0", Some(44690)),
 );
 
 declare_features! (
@@ -1114,12 +1117,28 @@ impl<'a> Context<'a> {
             // before the plugin attributes are registered
             // so we skip this then
             if !is_macro {
-                gate_feature!(self, custom_attribute, attr.span,
-                              &format!("The attribute `{}` is currently \
-                                        unknown to the compiler and \
-                                        may have meaning \
-                                        added to it in the future",
-                                       attr.path));
+                if attr.is_scoped() {
+                    gate_feature!(self, tool_attributes, attr.span,
+                                  &format!("scoped attribute `{}` is experimental", attr.path));
+                    if attr::is_known_tool(attr) {
+                        attr::mark_used(attr);
+                    } else {
+                        span_err!(
+                            self.parse_sess.span_diagnostic,
+                            attr.span,
+                            E0693,
+                            "An unkown tool name found in scoped attributes: `{}`.",
+                            attr.path
+                        );
+                    }
+                } else {
+                    gate_feature!(self, custom_attribute, attr.span,
+                                  &format!("The attribute `{}` is currently \
+                                            unknown to the compiler and \
+                                            may have meaning \
+                                            added to it in the future",
+                                           attr.path));
+                }
             }
         }
     }