Auto merge of #92294 - Kobzol:rustdoc-meta-kind, r=GuillaumeGomez

Add Attribute::meta_kind

The `AttrItem::meta` function is being called on a lot of places, however almost always the caller is only interested in the `kind` of the result `MetaItem`. Before, the `path`  had to be cloned in order to get the kind, now it does not have to be.

There is a larger related "problem". In a lot of places, something wants to know contents of attributes. This is accessed through `Attribute::meta_item_list`, which calls `AttrItem::meta` (now `AttrItem::meta_kind`), among other methods. When this function is called, the meta item list has to be recreated from scratch. Everytime something asks a simple question (like is this item/list of attributes `#[doc(hidden)]`?), the tokens of the attribute(s) are cloned, parsed and the results are allocated on the heap. That seems really unnecessary. What would be the best way to cache this? Turn `meta_item_list` into a query perhaps? Related PR: #92227

r? rust-lang/rustdoc

compiler/rustc_ast/src/attr/mod.rs

@@ -136,15 +136,15 @@ impl Attribute {
 
     pub fn value_str(&self) -> Option<Symbol> {
         match self.kind {
-            AttrKind::Normal(ref item, _) => item.meta(self.span).and_then(|meta| meta.value_str()),
+            AttrKind::Normal(ref item, _) => item.meta_kind().and_then(|kind| kind.value_str()),
             AttrKind::DocComment(..) => None,
         }
     }
 
     pub fn meta_item_list(&self) -> Option<Vec<NestedMetaItem>> {
         match self.kind {
-            AttrKind::Normal(ref item, _) => match item.meta(self.span) {
-                Some(MetaItem { kind: MetaItemKind::List(list), .. }) => Some(list),
+            AttrKind::Normal(ref item, _) => match item.meta_kind() {
+                Some(MetaItemKind::List(list)) => Some(list),
                 _ => None,
             },
             AttrKind::DocComment(..) => None,
@@ -228,6 +228,10 @@ impl AttrItem {
             span,
         })
     }
+
+    pub fn meta_kind(&self) -> Option<MetaItemKind> {
+        Some(MetaItemKind::from_mac_args(&self.args)?)
+    }
 }
 
 impl Attribute {
@@ -242,7 +246,7 @@ impl Attribute {
         match self.kind {
             AttrKind::DocComment(.., data) => Some(data),
             AttrKind::Normal(ref item, _) if item.path == sym::doc => {
-                item.meta(self.span).and_then(|meta| meta.value_str())
+                item.meta_kind().and_then(|kind| kind.value_str())
             }
             _ => None,
         }
@@ -270,6 +274,13 @@ impl Attribute {
         }
     }
 
+    pub fn meta_kind(&self) -> Option<MetaItemKind> {
+        match self.kind {
+            AttrKind::Normal(ref item, _) => item.meta_kind(),
+            AttrKind::DocComment(..) => None,
+        }
+    }
+
     pub fn tokens(&self) -> AttrAnnotatedTokenStream {
         match self.kind {
             AttrKind::Normal(_, ref tokens) => tokens
@@ -436,6 +447,16 @@ impl MetaItem {
 }
 
 impl MetaItemKind {
+    pub fn value_str(&self) -> Option<Symbol> {
+        match self {
+            MetaItemKind::NameValue(ref v) => match v.kind {
+                LitKind::Str(ref s, _) => Some(*s),
+                _ => None,
+            },
+            _ => None,
+        }
+    }
+
     pub fn mac_args(&self, span: Span) -> MacArgs {
         match self {
             MetaItemKind::Word => MacArgs::Empty,

compiler/rustc_interface/src/util.rs

@@ -484,7 +484,7 @@ pub(crate) fn check_attr_crate_type(
                     return;
                 }
 
-                if let ast::MetaItemKind::NameValue(spanned) = a.meta().unwrap().kind {
+                if let ast::MetaItemKind::NameValue(spanned) = a.meta_kind().unwrap() {
                     let span = spanned.span;
                     let lev_candidate = find_best_match_for_name(
                         &CRATE_TYPES.iter().map(|(k, _)| *k).collect::<Vec<_>>(),

compiler/rustc_passes/src/lib_features.rs

@@ -4,7 +4,7 @@
 // and `#[unstable (..)]`), but are not declared in one single location
 // (unlike lang features), which means we need to collect them instead.
 
-use rustc_ast::{Attribute, MetaItem, MetaItemKind};
+use rustc_ast::{Attribute, MetaItemKind};
 use rustc_errors::struct_span_err;
 use rustc_hir::intravisit::{NestedVisitorMap, Visitor};
 use rustc_middle::hir::map::Map;
@@ -34,8 +34,8 @@ impl<'tcx> LibFeatureCollector<'tcx> {
         // Find a stability attribute (i.e., `#[stable (..)]`, `#[unstable (..)]`,
         // `#[rustc_const_unstable (..)]`).
         if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| attr.has_name(**stab_attr)) {
-            let meta_item = attr.meta();
-            if let Some(MetaItem { kind: MetaItemKind::List(ref metas), .. }) = meta_item {
+            let meta_kind = attr.meta_kind();
+            if let Some(MetaItemKind::List(ref metas)) = meta_kind {
                 let mut feature = None;
                 let mut since = None;
                 for meta in metas {

compiler/rustc_typeck/src/collect.rs

@@ -2894,7 +2894,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
                 }
             }
         } else if attr.has_name(sym::instruction_set) {
-            codegen_fn_attrs.instruction_set = match attr.meta().map(|i| i.kind) {
+            codegen_fn_attrs.instruction_set = match attr.meta_kind() {
                 Some(MetaItemKind::List(ref items)) => match items.as_slice() {
                     [NestedMetaItem::MetaItem(set)] => {
                         let segments =
@@ -2999,7 +2999,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
         if !attr.has_name(sym::inline) {
             return ia;
         }
-        match attr.meta().map(|i| i.kind) {
+        match attr.meta_kind() {
             Some(MetaItemKind::Word) => InlineAttr::Hint,
             Some(MetaItemKind::List(ref items)) => {
                 inline_span = Some(attr.span);
@@ -3038,7 +3038,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
             return ia;
         }
         let err = |sp, s| struct_span_err!(tcx.sess.diagnostic(), sp, E0722, "{}", s).emit();
-        match attr.meta().map(|i| i.kind) {
+        match attr.meta_kind() {
             Some(MetaItemKind::Word) => {
                 err(attr.span, "expected one argument");
                 ia