Remove Session.used_attrs and move logic to CheckAttrVisitor

Instead of updating global state to mark attributes as used,
we now explicitly emit a warning when an attribute is used in
an unsupported position. As a side effect, we are to emit more
detailed warning messages (instead of just a generic "unused" message).

`Session.check_name` is removed, since its only purpose was to mark
the attribute as used. All of the callers are modified to use
`Attribute.has_name`

Additionally, `AttributeType::AssumedUsed` is removed - an 'assumed
used' attribute is implemented by simply not performing any checks
in `CheckAttrVisitor` for a particular attribute.

We no longer emit unused attribute warnings for the `#[rustc_dummy]`
attribute - it's an internal attribute used for tests, so it doesn't
mark sense to treat it as 'unused'.

With this commit, a large source of global untracked state is removed.

Cargo.lock

@@ -4115,10 +4115,12 @@ dependencies = [
  "rustc_attr",
  "rustc_data_structures",
  "rustc_errors",
+ "rustc_feature",
  "rustc_hir",
  "rustc_index",
  "rustc_lexer",
  "rustc_middle",
+ "rustc_parse",
  "rustc_serialize",
  "rustc_session",
  "rustc_span",

compiler/rustc_ast_lowering/src/lib.rs

@@ -2281,7 +2281,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     synthetic: param
                         .attrs
                         .iter()
-                        .filter(|attr| self.sess.check_name(attr, sym::rustc_synthetic))
+                        .filter(|attr| attr.has_name(sym::rustc_synthetic))
                         .map(|_| hir::SyntheticTyParamKind::FromAttr)
                         .next(),
                 };

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -268,7 +268,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             gate_feature_fn!(self, has_feature, attr.span, name, descr);
         }
         // Check unstable flavors of the `#[doc]` attribute.
-        if self.sess.check_name(attr, sym::doc) {
+        if attr.has_name(sym::doc) {
             for nested_meta in attr.meta_item_list().unwrap_or_default() {
                 macro_rules! gate_doc { ($($name:ident => $feature:ident)*) => {
                     $(if nested_meta.has_name(sym::$name) {
@@ -287,7 +287,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         }
 
         // Check for unstable modifiers on `#[link(..)]` attribute
-        if self.sess.check_name(attr, sym::link) {
+        if attr.has_name(sym::link) {
             for nested_meta in attr.meta_item_list().unwrap_or_default() {
                 if nested_meta.has_name(sym::modifiers) {
                     gate_feature_post!(
@@ -709,7 +709,7 @@ fn maybe_stage_features(sess: &Session, krate: &ast::Crate) {
 
     if !sess.opts.unstable_features.is_nightly_build() {
         let lang_features = &sess.features_untracked().declared_lang_features;
-        for attr in krate.attrs.iter().filter(|attr| sess.check_name(attr, sym::feature)) {
+        for attr in krate.attrs.iter().filter(|attr| attr.has_name(sym::feature)) {
             let mut err = struct_span_err!(
                 sess.parse_sess.span_diagnostic,
                 attr.span,

compiler/rustc_attr/src/builtin.rs

@@ -166,8 +166,6 @@ where
             continue; // not a stability level
         }
 
-        sess.mark_attr_used(attr);
-
         let meta = attr.meta();
 
         if attr.has_name(sym::rustc_promotable) {
@@ -636,8 +634,7 @@ where
     let diagnostic = &sess.parse_sess.span_diagnostic;
 
     'outer: for attr in attrs_iter {
-        if !(sess.check_name(attr, sym::deprecated) || sess.check_name(attr, sym::rustc_deprecated))
-        {
+        if !(attr.has_name(sym::deprecated) || attr.has_name(sym::rustc_deprecated)) {
             continue;
         }
 
@@ -700,17 +697,17 @@ where
                                     continue 'outer;
                                 }
                             }
-                            sym::note if sess.check_name(attr, sym::deprecated) => {
+                            sym::note if attr.has_name(sym::deprecated) => {
                                 if !get(mi, &mut note) {
                                     continue 'outer;
                                 }
                             }
-                            sym::reason if sess.check_name(attr, sym::rustc_deprecated) => {
+                            sym::reason if attr.has_name(sym::rustc_deprecated) => {
                                 if !get(mi, &mut note) {
                                     continue 'outer;
                                 }
                             }
-                            sym::suggestion if sess.check_name(attr, sym::rustc_deprecated) => {
+                            sym::suggestion if attr.has_name(sym::rustc_deprecated) => {
                                 if !get(mi, &mut suggestion) {
                                     continue 'outer;
                                 }
@@ -721,7 +718,7 @@ where
                                     meta.span(),
                                     AttrError::UnknownMetaItem(
                                         pprust::path_to_string(&mi.path),
-                                        if sess.check_name(attr, sym::deprecated) {
+                                        if attr.has_name(sym::deprecated) {
                                             &["since", "note"]
                                         } else {
                                             &["since", "reason", "suggestion"]
@@ -747,11 +744,11 @@ where
             }
         }
 
-        if suggestion.is_some() && sess.check_name(attr, sym::deprecated) {
+        if suggestion.is_some() && attr.has_name(sym::deprecated) {
             unreachable!("only allowed on rustc_deprecated")
         }
 
-        if sess.check_name(attr, sym::rustc_deprecated) {
+        if attr.has_name(sym::rustc_deprecated) {
             if since.is_none() {
                 handle_errors(&sess.parse_sess, attr.span, AttrError::MissingSince);
                 continue;
@@ -763,9 +760,7 @@ where
             }
         }
 
-        sess.mark_attr_used(&attr);
-
-        let is_since_rustc_version = sess.check_name(attr, sym::rustc_deprecated);
+        let is_since_rustc_version = attr.has_name(sym::rustc_deprecated);
         depr = Some((Deprecation { since, note, suggestion, is_since_rustc_version }, attr.span));
     }
 
@@ -816,7 +811,6 @@ pub fn find_repr_attrs(sess: &Session, attr: &Attribute) -> Vec<ReprAttr> {
     let diagnostic = &sess.parse_sess.span_diagnostic;
     if attr.has_name(sym::repr) {
         if let Some(items) = attr.meta_item_list() {
-            sess.mark_attr_used(attr);
             for item in items {
                 let mut recognised = false;
                 if item.is_word() {
@@ -1015,14 +1009,13 @@ pub enum TransparencyError {
 }
 
 pub fn find_transparency(
-    sess: &Session,
     attrs: &[Attribute],
     macro_rules: bool,
 ) -> (Transparency, Option<TransparencyError>) {
     let mut transparency = None;
     let mut error = None;
     for attr in attrs {
-        if sess.check_name(attr, sym::rustc_macro_transparency) {
+        if attr.has_name(sym::rustc_macro_transparency) {
             if let Some((_, old_span)) = transparency {
                 error = Some(TransparencyError::MultipleTransparencyAttrs(old_span, attr.span));
                 break;

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -677,8 +677,6 @@ impl<'a> TraitDef<'a> {
         let self_type = cx.ty_path(path);
 
         let attr = cx.attribute(cx.meta_word(self.span, sym::automatically_derived));
-        // Just mark it now since we know that it'll end up used downstream
-        cx.sess.mark_attr_used(&attr);
         let opt_trait_ref = Some(trait_ref);
         let unused_qual = {
             let word = rustc_ast::attr::mk_nested_word_item(Ident::new(

compiler/rustc_builtin_macros/src/proc_macro_harness.rs

@@ -260,11 +260,11 @@ impl<'a> Visitor<'a> for CollectProcMacros<'a> {
             return;
         }
 
-        if self.sess.check_name(attr, sym::proc_macro_derive) {
+        if attr.has_name(sym::proc_macro_derive) {
             self.collect_custom_derive(item, attr);
-        } else if self.sess.check_name(attr, sym::proc_macro_attribute) {
+        } else if attr.has_name(sym::proc_macro_attribute) {
             self.collect_attr_proc_macro(item);
-        } else if self.sess.check_name(attr, sym::proc_macro) {
+        } else if attr.has_name(sym::proc_macro) {
             self.collect_bang_proc_macro(item);
         };
 

compiler/rustc_builtin_macros/src/test_harness.rs

@@ -188,8 +188,7 @@ impl<'a> MutVisitor for EntryPointCleaner<'a> {
                     let attrs = attrs
                         .into_iter()
                         .filter(|attr| {
-                            !self.sess.check_name(attr, sym::rustc_main)
-                                && !self.sess.check_name(attr, sym::start)
+                            !attr.has_name(sym::rustc_main) && !attr.has_name(sym::start)
                         })
                         .chain(iter::once(allow_dead_code))
                         .collect();

compiler/rustc_expand/src/config.rs

@@ -5,7 +5,7 @@ use rustc_ast::token::{DelimToken, Token, TokenKind};
 use rustc_ast::tokenstream::{AttrAnnotatedTokenStream, AttrAnnotatedTokenTree};
 use rustc_ast::tokenstream::{DelimSpan, Spacing};
 use rustc_ast::tokenstream::{LazyTokenStream, TokenTree};
-use rustc_ast::{self as ast, AstLike, AttrItem, AttrStyle, Attribute, MetaItem};
+use rustc_ast::{self as ast, AstLike, AttrStyle, Attribute, MetaItem};
 use rustc_attr as attr;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::map_in_place::MapInPlace;
@@ -14,7 +14,7 @@ use rustc_feature::{Feature, Features, State as FeatureState};
 use rustc_feature::{
     ACCEPTED_FEATURES, ACTIVE_FEATURES, REMOVED_FEATURES, STABLE_REMOVED_FEATURES,
 };
-use rustc_parse::{parse_in, validate_attr};
+use rustc_parse::validate_attr;
 use rustc_session::parse::feature_err;
 use rustc_session::Session;
 use rustc_span::edition::{Edition, ALL_EDITIONS};
@@ -75,7 +75,7 @@ fn get_features(
     // Process the edition umbrella feature-gates first, to ensure
     // `edition_enabled_features` is completed before it's queried.
     for attr in krate_attrs {
-        if !sess.check_name(attr, sym::feature) {
+        if !attr.has_name(sym::feature) {
             continue;
         }
 
@@ -108,7 +108,7 @@ fn get_features(
     }
 
     for attr in krate_attrs {
-        if !sess.check_name(attr, sym::feature) {
+        if !attr.has_name(sym::feature) {
             continue;
         }
 
@@ -237,11 +237,6 @@ macro_rules! configure {
     };
 }
 
-const CFG_ATTR_GRAMMAR_HELP: &str = "#[cfg_attr(condition, attribute, other_attribute, ...)]";
-const CFG_ATTR_NOTE_REF: &str = "for more information, visit \
-    <https://doc.rust-lang.org/reference/conditional-compilation.html\
-    #the-cfg_attr-attribute>";
-
 impl<'a> StripUnconfigured<'a> {
     pub fn configure<T: AstLike>(&mut self, mut node: T) -> Option<T> {
         self.process_cfg_attrs(&mut node);
@@ -349,19 +344,17 @@ impl<'a> StripUnconfigured<'a> {
             return vec![attr];
         }
 
-        let (cfg_predicate, expanded_attrs) = match self.parse_cfg_attr(&attr) {
-            None => return vec![],
-            Some(r) => r,
-        };
+        let (cfg_predicate, expanded_attrs) =
+            match rustc_parse::parse_cfg_attr(&attr, &self.sess.parse_sess) {
+                None => return vec![],
+                Some(r) => r,
+            };
 
         // Lint on zero attributes in source.
         if expanded_attrs.is_empty() {
             return vec![attr];
         }
 
-        // At this point we know the attribute is considered used.
-        self.sess.mark_attr_used(&attr);
-
         if !attr::cfg_matches(&cfg_predicate, &self.sess.parse_sess, self.features) {
             return vec![];
         }
@@ -415,46 +408,10 @@ impl<'a> StripUnconfigured<'a> {
             .collect()
     }
 
-    fn parse_cfg_attr(&self, attr: &Attribute) -> Option<(MetaItem, Vec<(AttrItem, Span)>)> {
-        match attr.get_normal_item().args {
-            ast::MacArgs::Delimited(dspan, delim, ref tts) if !tts.is_empty() => {
-                let msg = "wrong `cfg_attr` delimiters";
-                validate_attr::check_meta_bad_delim(&self.sess.parse_sess, dspan, delim, msg);
-                match parse_in(&self.sess.parse_sess, tts.clone(), "`cfg_attr` input", |p| {
-                    p.parse_cfg_attr()
-                }) {
-                    Ok(r) => return Some(r),
-                    Err(mut e) => {
-                        e.help(&format!("the valid syntax is `{}`", CFG_ATTR_GRAMMAR_HELP))
-                            .note(CFG_ATTR_NOTE_REF)
-                            .emit();
-                    }
-                }
-            }
-            _ => self.error_malformed_cfg_attr_missing(attr.span),
-        }
-        None
-    }
-
-    fn error_malformed_cfg_attr_missing(&self, span: Span) {
-        self.sess
-            .parse_sess
-            .span_diagnostic
-            .struct_span_err(span, "malformed `cfg_attr` attribute input")
-            .span_suggestion(
-                span,
-                "missing condition and attribute",
-                CFG_ATTR_GRAMMAR_HELP.to_string(),
-                Applicability::HasPlaceholders,
-            )
-            .note(CFG_ATTR_NOTE_REF)
-            .emit();
-    }
-
     /// Determines if a node with the given attributes should be included in this configuration.
     fn in_cfg(&self, attrs: &[Attribute]) -> bool {
         attrs.iter().all(|attr| {
-            if !is_cfg(self.sess, attr) {
+            if !is_cfg(attr) {
                 return true;
             }
             let meta_item = match validate_attr::parse_meta(&self.sess.parse_sess, attr) {
@@ -500,7 +457,7 @@ impl<'a> StripUnconfigured<'a> {
         //
         // N.B., this is intentionally not part of the visit_expr() function
         //     in order for filter_map_expr() to be able to avoid this check
-        if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(self.sess, a)) {
+        if let Some(attr) = expr.attrs().iter().find(|a| is_cfg(*a)) {
             let msg = "removing an expression is not supported in this position";
             self.sess.parse_sess.span_diagnostic.span_err(attr.span, msg);
         }
@@ -536,6 +493,6 @@ pub fn parse_cfg<'a>(meta_item: &'a MetaItem, sess: &Session) -> Option<&'a Meta
     }
 }
 
-fn is_cfg(sess: &Session, attr: &Attribute) -> bool {
-    sess.check_name(attr, sym::cfg)
+fn is_cfg(attr: &Attribute) -> bool {
+    attr.has_name(sym::cfg)
 }

compiler/rustc_expand/src/expand.rs

@@ -753,11 +753,8 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         }
                     }
                 }
-                SyntaxExtensionKind::NonMacroAttr { mark_used } => {
+                SyntaxExtensionKind::NonMacroAttr { mark_used: _ } => {
                     self.cx.expanded_inert_attrs.mark(&attr);
-                    if *mark_used {
-                        self.cx.sess.mark_attr_used(&attr);
-                    }
                     item.visit_attrs(|attrs| attrs.insert(pos, attr));
                     fragment_kind.expect_from_annotatables(iter::once(item))
                 }

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -535,7 +535,7 @@ pub fn compile_declarative_macro(
 
     valid &= macro_check::check_meta_variables(&sess.parse_sess, def.id, def.span, &lhses, &rhses);
 
-    let (transparency, transparency_error) = attr::find_transparency(sess, &def.attrs, macro_rules);
+    let (transparency, transparency_error) = attr::find_transparency(&def.attrs, macro_rules);
     match transparency_error {
         Some(TransparencyError::UnknownTransparency(value, span)) => {
             diag.span_err(span, &format!("unknown macro transparency: `{}`", value))