Address review comments

src/librustc_parse/lib.rs

@@ -277,6 +277,8 @@ pub fn parse_in_attr<'a, T>(
 ) -> PResult<'a, T> {
     let mut parser = Parser::new(
         sess,
+        // FIXME(#66940, Centril | petrochenkov): refactor this function so it doesn't
+        // require reconstructing and immediately re-parsing delimiters.
         attr.get_normal_item().args.outer_tokens(),
         None,
         false,

src/librustc_parse/parser/mod.rs

@@ -1024,7 +1024,8 @@ impl<'a> Parser<'a> {
                        self.check(&token::OpenDelim(DelimToken::Brace)) {
             match self.parse_token_tree() {
                 TokenTree::Delimited(dspan, delim, tokens) =>
-                    MacArgs::Delimited(dspan, MacDelimiter::from_token(delim), tokens),
+                    // We've confirmed above that there is a delimiter so unwrapping is OK.
+                    MacArgs::Delimited(dspan, MacDelimiter::from_token(delim).unwrap(), tokens),
                 _ => unreachable!(),
             }
         } else if !delimited_only {

src/libsyntax/ast.rs

@@ -1396,8 +1396,12 @@ pub enum MacArgs {
     /// Delimited arguments - `#[attr()/[]/{}]` or `mac!()/[]/{}`.
     Delimited(DelimSpan, MacDelimiter, TokenStream),
     /// Arguments of a key-value attribute - `#[attr = "value"]`.
-    /// Span belongs to the `=` token, token stream is the "value".
+    Eq(
-    Eq(Span, TokenStream),
+        /// Span of the `=` token.
+        Span,
+        /// Token stream of the "value".
+        TokenStream,
+    ),
 }
 
 impl MacArgs {
@@ -1421,13 +1425,13 @@ impl MacArgs {
     pub fn inner_tokens(&self) -> TokenStream {
         match self {
             MacArgs::Empty => TokenStream::default(),
-            MacArgs::Delimited(.., tokens) => tokens.clone(),
+            MacArgs::Delimited(.., tokens) |
             MacArgs::Eq(.., tokens) => tokens.clone(),
         }
     }
 
     /// Tokens together with the delimiters or `=`.
-    /// Use of this functions generally means that something suboptimal or hacky is happening.
+    /// Use of this method generally means that something suboptimal or hacky is happening.
     pub fn outer_tokens(&self) -> TokenStream {
         match *self {
             MacArgs::Empty => TokenStream::default(),
@@ -1461,12 +1465,12 @@ impl MacDelimiter {
         }
     }
 
-    pub fn from_token(delim: DelimToken) -> MacDelimiter {
+    pub fn from_token(delim: DelimToken) -> Option<MacDelimiter> {
         match delim {
-            token::Paren => MacDelimiter::Parenthesis,
+            token::Paren => Some(MacDelimiter::Parenthesis),
-            token::Bracket => MacDelimiter::Bracket,
+            token::Bracket => Some(MacDelimiter::Bracket),
-            token::Brace => MacDelimiter::Brace,
+            token::Brace => Some(MacDelimiter::Brace),
-            token::NoDelim => panic!("expected a delimiter"),
+            token::NoDelim => None,
         }
     }
 }