Add support for registering attributes with rustc in plugins

This lets plugin authors opt attributes out of the `custom_attribute`
and `unused_attribute` checks.

Author: Manishearth

src/librustc/plugin/registry.rs

@@ -20,6 +20,7 @@ use syntax::codemap::Span;
 use syntax::parse::token;
 use syntax::ptr::P;
 use syntax::ast;
+use syntax::feature_gate::AttributeType;
 
 use std::collections::HashMap;
 use std::borrow::ToOwned;
@@ -54,6 +55,9 @@ pub struct Registry<'a> {
 
     #[doc(hidden)]
     pub llvm_passes: Vec<String>,
+
+    #[doc(hidden)]
+    pub attributes: Vec<(String, AttributeType)>,
 }
 
 impl<'a> Registry<'a> {
@@ -67,6 +71,7 @@ impl<'a> Registry<'a> {
             lint_passes: vec!(),
             lint_groups: HashMap::new(),
             llvm_passes: vec!(),
+            attributes: vec!(),
         }
     }
 
@@ -130,4 +135,22 @@ impl<'a> Registry<'a> {
     pub fn register_llvm_pass(&mut self, name: &str) {
         self.llvm_passes.push(name.to_owned());
     }
+
+
+    /// Register an attribute with an attribute type
+    ///
+    /// Registered attributes will bypass the `custom_attribute` feature gate
+    ///
+    /// `Whitelisted` attributes will additionally not trigger the `unused_attribute`
+    /// lint
+    ///
+    /// `CrateLevel` attributes will not be allowed on anything other than a crate
+    pub fn register_attribute(&mut self, name: String, ty: AttributeType) {
+        if let AttributeType::Gated(..) = ty {
+            self.sess.err("plugin tried to register a gated attribute. \
+                           Only `Normal`, `Whitelisted`, and `CrateLevel` \
+                           attributes are allowed");
+        }
+        self.attributes.push((name, ty));
+    }
 }

src/librustc/session/mod.rs

@@ -23,6 +23,7 @@ use syntax::parse;
 use syntax::parse::token;
 use syntax::parse::ParseSess;
 use syntax::{ast, codemap};
+use syntax::feature_gate::AttributeType;
 
 use rustc_back::target::Target;
 
@@ -54,6 +55,7 @@ pub struct Session {
     pub lint_store: RefCell<lint::LintStore>,
     pub lints: RefCell<NodeMap<Vec<(lint::LintId, codemap::Span, String)>>>,
     pub plugin_llvm_passes: RefCell<Vec<String>>,
+    pub plugin_attributes: RefCell<Vec<(String, AttributeType)>>,
     pub crate_types: RefCell<Vec<config::CrateType>>,
     pub crate_metadata: RefCell<Vec<String>>,
     pub features: RefCell<feature_gate::Features>,
@@ -416,6 +418,7 @@ pub fn build_session_(sopts: config::Options,
         lint_store: RefCell::new(lint::LintStore::new()),
         lints: RefCell::new(NodeMap()),
         plugin_llvm_passes: RefCell::new(Vec::new()),
+        plugin_attributes: RefCell::new(Vec::new()),
         crate_types: RefCell::new(Vec::new()),
         crate_metadata: RefCell::new(Vec::new()),
         delayed_span_bug: RefCell::new(None),

src/librustc_driver/driver.rs

@@ -444,7 +444,8 @@ pub fn phase_2_configure_and_expand(sess: &Session,
         }
     });
 
-    let Registry { syntax_exts, lint_passes, lint_groups, llvm_passes, .. } = registry;
+    let Registry { syntax_exts, lint_passes, lint_groups,
+                   llvm_passes, attributes, .. } = registry;
 
     {
         let mut ls = sess.lint_store.borrow_mut();
@@ -457,6 +458,7 @@ pub fn phase_2_configure_and_expand(sess: &Session,
         }
 
         *sess.plugin_llvm_passes.borrow_mut() = llvm_passes;
+        *sess.plugin_attributes.borrow_mut() = attributes.clone();
     }
 
     // Lint plugins are registered; now we can process command line flags.
@@ -511,7 +513,7 @@ pub fn phase_2_configure_and_expand(sess: &Session,
         let features =
             syntax::feature_gate::check_crate(sess.codemap(),
                                               &sess.parse_sess.span_diagnostic,
-                                              &krate);
+                                              &krate, &attributes);
         *sess.features.borrow_mut() = features;
         sess.abort_if_errors();
     });
@@ -541,7 +543,7 @@ pub fn phase_2_configure_and_expand(sess: &Session,
         let features =
             syntax::feature_gate::check_crate(sess.codemap(),
                                               &sess.parse_sess.span_diagnostic,
-                                              &krate);
+                                              &krate, &attributes);
         *sess.features.borrow_mut() = features;
         sess.abort_if_errors();
     });

src/librustc_lint/builtin.rs

@@ -641,9 +641,23 @@ impl LintPass for UnusedAttributes {
             }
         }
 
+        let plugin_attributes = cx.sess().plugin_attributes.borrow_mut();
+        for &(ref name, ty) in plugin_attributes.iter() {
+            match ty {
+                AttributeType::Whitelisted if attr.check_name(&*name) => {
+                    break;
+                },
+                _ => ()
+            }
+        }
+
         if !attr::is_used(attr) {
             cx.span_lint(UNUSED_ATTRIBUTES, attr.span, "unused attribute");
-            if KNOWN_ATTRIBUTES.contains(&(&attr.name(), AttributeType::CrateLevel)) {
+            if KNOWN_ATTRIBUTES.contains(&(&attr.name(), AttributeType::CrateLevel)) ||
+               plugin_attributes.iter()
+                                .find(|&&(ref x, t)| &*attr.name() == &*x &&
+                                                     AttributeType::CrateLevel == t)
+                                .is_some() {
                 let msg = match attr.node.style {
                     ast::AttrOuter => "crate-level attribute should be an inner \
                                        attribute: add an exclamation mark: #![foo]",

src/libsyntax/feature_gate.rs

@@ -359,6 +359,7 @@ struct Context<'a> {
     features: Vec<&'static str>,
     span_handler: &'a SpanHandler,
     cm: &'a CodeMap,
+    plugin_attributes: &'a [(String, AttributeType)],
 }
 
 impl<'a> Context<'a> {
@@ -373,7 +374,7 @@ impl<'a> Context<'a> {
         self.features.iter().any(|&n| n == feature)
     }
 
-    fn check_attribute(&self, attr: &ast::Attribute) {
+    fn check_attribute(&self, attr: &ast::Attribute, is_macro: bool) {
         debug!("check_attribute(attr = {:?})", attr);
         let name = &*attr.name();
         for &(n, ty) in KNOWN_ATTRIBUTES {
@@ -385,6 +386,13 @@ impl<'a> Context<'a> {
                 return;
             }
         }
+        for &(ref n, ref ty) in self.plugin_attributes.iter() {
+            if &*n == name {
+                // Plugins can't gate attributes, so we don't check for it
+                debug!("check_attribute: {:?} is registered by a plugin, {:?}", name, ty);
+                return;
+            }
+        }
         if name.starts_with("rustc_") {
             self.gate_feature("rustc_attrs", attr.span,
                               "unless otherwise specified, attributes \
@@ -395,12 +403,15 @@ impl<'a> Context<'a> {
                               "attributes of the form `#[derive_*]` are reserved \
                                for the compiler");
         } else {
-            self.gate_feature("custom_attribute", attr.span,
-                       &format!("The attribute `{}` is currently \
-                                unknown to the compiler and \
-                                may have meaning \
-                                added to it in the future",
-                                name));
+            // Only do the custom attribute lint post-expansion
+            if !is_macro {
+                self.gate_feature("custom_attribute", attr.span,
+                           &format!("The attribute `{}` is currently \
+                                    unknown to the compiler and \
+                                    may have meaning \
+                                    added to it in the future",
+                                    name));
+            }
         }
     }
 }
@@ -479,7 +490,7 @@ impl<'a, 'v> Visitor<'v> for MacroVisitor<'a> {
     }
 
     fn visit_attribute(&mut self, attr: &'v ast::Attribute) {
-        self.context.check_attribute(attr);
+        self.context.check_attribute(attr, true);
     }
 }
 
@@ -498,7 +509,7 @@ impl<'a> PostExpansionVisitor<'a> {
 impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
     fn visit_attribute(&mut self, attr: &ast::Attribute) {
         if !self.context.cm.span_allows_unstable(attr.span) {
-            self.context.check_attribute(attr);
+            self.context.check_attribute(attr, false);
         }
     }
 
@@ -685,6 +696,7 @@ impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
 
 fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler,
                         krate: &ast::Crate,
+                        plugin_attributes: &[(String, AttributeType)],
                         check: F)
                        -> Features
     where F: FnOnce(&mut Context, &ast::Crate)
@@ -693,6 +705,7 @@ fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler,
         features: Vec::new(),
         span_handler: span_handler,
         cm: cm,
+        plugin_attributes: plugin_attributes,
     };
 
     let mut accepted_features = Vec::new();
@@ -765,14 +778,14 @@ fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler,
 
 pub fn check_crate_macros(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 -> Features {
-    check_crate_inner(cm, span_handler, krate,
+    check_crate_inner(cm, span_handler, krate, &[] as &'static [_],
                       |ctx, krate| visit::walk_crate(&mut MacroVisitor { context: ctx }, krate))
 }
 
-pub fn check_crate(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
-                   -> Features
+pub fn check_crate(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate,
+                   plugin_attributes: &[(String, AttributeType)]) -> Features
 {
-    check_crate_inner(cm, span_handler, krate,
+    check_crate_inner(cm, span_handler, krate, plugin_attributes,
                       |ctx, krate| visit::walk_crate(&mut PostExpansionVisitor { context: ctx },
                                                      krate))
 }