Unconditionally capture tokens for attributes.

This allows us to avoid synthesizing tokens in `prepend_attr`, since we
have the original tokens available.

We still need to synthesize tokens when expanding `cfg_attr`,
but this is an unavoidable consequence of the syntax of `cfg_attr` -
the user does not supply the `#` and `[]` tokens that a `cfg_attr`
expands to.

Author: Aaron1011

Diff for: compiler/rustc_ast/src/ast.rs

@@ -2423,6 +2423,7 @@ pub struct Attribute {
     /// or the construct this attribute is contained within (inner).
     pub style: AttrStyle,
     pub span: Span,
+    pub tokens: Option<LazyTokenStream>,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug)]

Diff for: compiler/rustc_ast/src/attr/mod.rs

@@ -325,7 +325,7 @@ pub fn mk_attr(style: AttrStyle, path: Path, args: MacArgs, span: Span) -> Attri
 }
 
 pub fn mk_attr_from_item(style: AttrStyle, item: AttrItem, span: Span) -> Attribute {
-    Attribute { kind: AttrKind::Normal(item), id: mk_attr_id(), style, span }
+    Attribute { kind: AttrKind::Normal(item), id: mk_attr_id(), style, span, tokens: None }
 }
 
 /// Returns an inner attribute with the given value and span.
@@ -344,7 +344,13 @@ pub fn mk_doc_comment(
     data: Symbol,
     span: Span,
 ) -> Attribute {
-    Attribute { kind: AttrKind::DocComment(comment_kind, data), id: mk_attr_id(), style, span }
+    Attribute {
+        kind: AttrKind::DocComment(comment_kind, data),
+        id: mk_attr_id(),
+        style,
+        span,
+        tokens: None,
+    }
 }
 
 pub fn list_contains_name(items: &[NestedMetaItem], name: Symbol) -> bool {

Diff for: compiler/rustc_ast/src/mut_visit.rs

@@ -577,7 +577,7 @@ pub fn noop_visit_local<T: MutVisitor>(local: &mut P<Local>, vis: &mut T) {
 }
 
 pub fn noop_visit_attribute<T: MutVisitor>(attr: &mut Attribute, vis: &mut T) {
-    let Attribute { kind, id: _, style: _, span } = attr;
+    let Attribute { kind, id: _, style: _, span, tokens: _ } = attr;
     match kind {
         AttrKind::Normal(AttrItem { path, args, tokens: _ }) => {
             vis.visit_path(path);

Diff for: compiler/rustc_ast_lowering/src/expr.rs

@@ -210,9 +210,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         ex.span = e.span;
                     }
                     // Merge attributes into the inner expression.
-                    let mut attrs = e.attrs.clone();
+                    let mut attrs: Vec<_> = e.attrs.iter().map(|a| self.lower_attr(a)).collect();
                     attrs.extend::<Vec<_>>(ex.attrs.into());
-                    ex.attrs = attrs;
+                    ex.attrs = attrs.into();
                     return ex;
                 }
 
@@ -1471,13 +1471,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
             hir::MatchSource::ForLoopDesugar,
         ));
 
+        let attrs: Vec<_> = e.attrs.iter().map(|a| self.lower_attr(a)).collect();
+
         // This is effectively `{ let _result = ...; _result }`.
         // The construct was introduced in #21984 and is necessary to make sure that
         // temporaries in the `head` expression are dropped and do not leak to the
         // surrounding scope of the `match` since the `match` is not a terminating scope.
         //
         // Also, add the attributes to the outer returned expr node.
-        self.expr_drop_temps_mut(desugared_span, match_expr, e.attrs.clone())
+        self.expr_drop_temps_mut(desugared_span, match_expr, attrs.into())
     }
 
     /// Desugar `ExprKind::Try` from: `<expr>?` into:

Diff for: compiler/rustc_ast_lowering/src/lib.rs

@@ -972,7 +972,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
         };
 
-        Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
+        // Tokens aren't needed after macro expansion and parsing
+        Attribute { kind, id: attr.id, style: attr.style, span: attr.span, tokens: None }
     }
 
     fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
@@ -1713,7 +1714,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 pat: self.lower_pat(&l.pat),
                 init,
                 span: l.span,
-                attrs: l.attrs.clone(),
+                attrs: l.attrs.iter().map(|a| self.lower_attr(a)).collect::<Vec<_>>().into(),
                 source: hir::LocalSource::Normal,
             },
             ids,

Diff for: compiler/rustc_builtin_macros/src/cmdline_attrs.rs

@@ -15,7 +15,7 @@ pub fn inject(mut krate: ast::Crate, parse_sess: &ParseSess, attrs: &[String]) -
         );
 
         let start_span = parser.token.span;
-        let AttrItem { path, args, tokens: _ } = match parser.parse_attr_item() {
+        let AttrItem { path, args, tokens: _ } = match parser.parse_attr_item(false) {
             Ok(ai) => ai,
             Err(mut err) => {
                 err.emit();

Diff for: compiler/rustc_expand/src/config.rs

@@ -3,10 +3,13 @@
 use rustc_ast::attr::HasAttrs;
 use rustc_ast::mut_visit::*;
 use rustc_ast::ptr::P;
+use rustc_ast::token::{DelimToken, Token, TokenKind};
+use rustc_ast::tokenstream::{DelimSpan, LazyTokenStreamInner, Spacing, TokenStream, TokenTree};
 use rustc_ast::{self as ast, AttrItem, Attribute, MetaItem};
 use rustc_attr as attr;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::map_in_place::MapInPlace;
+use rustc_data_structures::sync::Lrc;
 use rustc_errors::{error_code, struct_span_err, Applicability, Handler};
 use rustc_feature::{Feature, Features, State as FeatureState};
 use rustc_feature::{
@@ -289,7 +292,37 @@ impl<'a> StripUnconfigured<'a> {
         expanded_attrs
             .into_iter()
             .flat_map(|(item, span)| {
-                let attr = attr::mk_attr_from_item(attr.style, item, span);
+                let orig_tokens =
+                    attr.tokens.as_ref().unwrap_or_else(|| panic!("Missing tokens for {:?}", attr));
+
+                // We are taking an attribute of the form `#[cfg_attr(pred, attr)]`
+                // and producing an attribute of the form `#[attr]`. We
+                // have captured tokens for `attr` itself, but we need to
+                // synthesize tokens for the wrapper `#` and `[]`, which
+                // we do below.
+
+                // Use the `#` in `#[cfg_attr(pred, attr)]` as the `#` token
+                // for `attr` when we expand it to `#[attr]`
+                let pound_token = orig_tokens.into_token_stream().trees().next().unwrap();
+                if !matches!(pound_token, TokenTree::Token(Token { kind: TokenKind::Pound, .. })) {
+                    panic!("Bad tokens for attribute {:?}", attr);
+                }
+                // We don't really have a good span to use for the syntheized `[]`
+                // in `#[attr]`, so just use the span of the `#` token.
+                let bracket_group = TokenTree::Delimited(
+                    DelimSpan::from_single(pound_token.span()),
+                    DelimToken::Bracket,
+                    item.tokens
+                        .clone()
+                        .unwrap_or_else(|| panic!("Missing tokens for {:?}", item))
+                        .into_token_stream(),
+                );
+
+                let mut attr = attr::mk_attr_from_item(attr.style, item, span);
+                attr.tokens = Some(Lrc::new(LazyTokenStreamInner::Ready(TokenStream::new(vec![
+                    (pound_token, Spacing::Alone),
+                    (bracket_group, Spacing::Alone),
+                ]))));
                 self.process_cfg_attr(attr)
             })
             .collect()

Diff for: compiler/rustc_expand/src/expand.rs

@@ -1785,6 +1785,7 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
                 span: at.span,
                 id: at.id,
                 style: at.style,
+                tokens: None,
             };
         } else {
             noop_visit_attribute(at, self)

Diff for: compiler/rustc_middle/src/ich/impls_syntax.rs

@@ -40,11 +40,12 @@ impl<'ctx> rustc_ast::HashStableContext for StableHashingContext<'ctx> {
         debug_assert!(!attr.ident().map_or(false, |ident| self.is_ignored_attr(ident.name)));
         debug_assert!(!attr.is_doc_comment());
 
-        let ast::Attribute { kind, id: _, style, span } = attr;
+        let ast::Attribute { kind, id: _, style, span, tokens } = attr;
         if let ast::AttrKind::Normal(item) = kind {
             item.hash_stable(self, hasher);
             style.hash_stable(self, hasher);
             span.hash_stable(self, hasher);
+            tokens.as_ref().expect_none("Tokens should have been removed during lowering!");
         } else {
             unreachable!();
         }

Diff for: compiler/rustc_parse/src/lib.rs

@@ -252,9 +252,7 @@ pub fn nt_to_tokenstream(nt: &Nonterminal, sess: &ParseSess, span: Span) -> Toke
     let convert_tokens = |tokens: Option<LazyTokenStream>| tokens.map(|t| t.into_token_stream());
 
     let tokens = match *nt {
-        Nonterminal::NtItem(ref item) => {
-            prepend_attrs(sess, &item.attrs, item.tokens.as_ref(), span)
-        }
+        Nonterminal::NtItem(ref item) => prepend_attrs(&item.attrs, item.tokens.as_ref()),
         Nonterminal::NtBlock(ref block) => convert_tokens(block.tokens.clone()),
         Nonterminal::NtStmt(ref stmt) => {
             // FIXME: We currently only collect tokens for `:stmt`
@@ -279,7 +277,7 @@ pub fn nt_to_tokenstream(nt: &Nonterminal, sess: &ParseSess, span: Span) -> Toke
             if expr.tokens.is_none() {
                 debug!("missing tokens for expr {:?}", expr);
             }
-            prepend_attrs(sess, &expr.attrs, expr.tokens.as_ref(), span)
+            prepend_attrs(&expr.attrs, expr.tokens.as_ref())
         }
     };
 
@@ -603,10 +601,8 @@ fn token_probably_equal_for_proc_macro(first: &Token, other: &Token) -> bool {
 }
 
 fn prepend_attrs(
-    sess: &ParseSess,
     attrs: &[ast::Attribute],
     tokens: Option<&tokenstream::LazyTokenStream>,
-    span: rustc_span::Span,
 ) -> Option<tokenstream::TokenStream> {
     let tokens = tokens?.clone().into_token_stream();
     if attrs.is_empty() {
@@ -619,47 +615,12 @@ fn prepend_attrs(
             ast::AttrStyle::Outer,
             "inner attributes should prevent cached tokens from existing"
         );
-
-        let source = pprust::attribute_to_string(attr);
-        let macro_filename = FileName::macro_expansion_source_code(&source);
-
-        let item = match attr.kind {
-            ast::AttrKind::Normal(ref item) => item,
-            ast::AttrKind::DocComment(..) => {
-                let stream = parse_stream_from_source_str(macro_filename, source, sess, Some(span));
-                builder.push(stream);
-                continue;
-            }
-        };
-
-        // synthesize # [ $path $tokens ] manually here
-        let mut brackets = tokenstream::TokenStreamBuilder::new();
-
-        // For simple paths, push the identifier directly
-        if item.path.segments.len() == 1 && item.path.segments[0].args.is_none() {
-            let ident = item.path.segments[0].ident;
-            let token = token::Ident(ident.name, ident.as_str().starts_with("r#"));
-            brackets.push(tokenstream::TokenTree::token(token, ident.span));
-
-        // ... and for more complicated paths, fall back to a reparse hack that
-        // should eventually be removed.
-        } else {
-            let stream = parse_stream_from_source_str(macro_filename, source, sess, Some(span));
-            brackets.push(stream);
-        }
-
-        brackets.push(item.args.outer_tokens());
-
-        // The span we list here for `#` and for `[ ... ]` are both wrong in
-        // that it encompasses more than each token, but it hopefully is "good
-        // enough" for now at least.
-        builder.push(tokenstream::TokenTree::token(token::Pound, attr.span));
-        let delim_span = tokenstream::DelimSpan::from_single(attr.span);
-        builder.push(tokenstream::TokenTree::Delimited(
-            delim_span,
-            token::DelimToken::Bracket,
-            brackets.build(),
-        ));
+        builder.push(
+            attr.tokens
+                .clone()
+                .unwrap_or_else(|| panic!("Attribute {:?} is missing tokens!", attr))
+                .into_token_stream(),
+        );
     }
     builder.push(tokens.clone());
     Some(builder.build())