Rollup merge of #147481 - hkBst:format-1, r=jackh726

format: some small cleanup

Some small cleanup and some additional comments I did while trying to understand this code.

Author: Zalathar

compiler/rustc_ast/src/token.rs

@@ -881,11 +881,11 @@ impl Token {
     }
 
     pub fn is_qpath_start(&self) -> bool {
-        self == &Lt || self == &Shl
+        matches!(self.kind, Lt | Shl)
     }
 
     pub fn is_path_start(&self) -> bool {
-        self == &PathSep
+        self.kind == PathSep
             || self.is_qpath_start()
             || matches!(self.is_metavar_seq(), Some(MetaVarKind::Path))
             || self.is_path_segment_keyword()

compiler/rustc_builtin_macros/src/format.rs

@@ -69,35 +69,26 @@ struct MacroInput {
 /// Ok((fmtstr, parsed arguments))
 /// ```
 fn parse_args<'a>(ecx: &ExtCtxt<'a>, sp: Span, tts: TokenStream) -> PResult<'a, MacroInput> {
-    let mut args = FormatArguments::new();
-
     let mut p = ecx.new_parser_from_tts(tts);
 
-    if p.token == token::Eof {
-        return Err(ecx.dcx().create_err(errors::FormatRequiresString { span: sp }));
-    }
-
-    let first_token = &p.token;
-
-    let fmtstr = if let token::Literal(lit) = first_token.kind
-        && matches!(lit.kind, token::Str | token::StrRaw(_))
-    {
+    // parse the format string
+    let fmtstr = match p.token.kind {
+        token::Eof => return Err(ecx.dcx().create_err(errors::FormatRequiresString { span: sp })),
         // This allows us to properly handle cases when the first comma
         // after the format string is mistakenly replaced with any operator,
         // which cause the expression parser to eat too much tokens.
-        p.parse_literal_maybe_minus()?
-    } else {
+        token::Literal(token::Lit { kind: token::Str | token::StrRaw(_), .. }) => {
+            p.parse_literal_maybe_minus()?
+        }
         // Otherwise, we fall back to the expression parser.
-        p.parse_expr()?
+        _ => p.parse_expr()?,
     };
 
-    // Only allow implicit captures to be used when the argument is a direct literal
-    // instead of a macro expanding to one.
-    let is_direct_literal = matches!(fmtstr.kind, ExprKind::Lit(_));
-
+    // parse comma FormatArgument pairs
+    let mut args = FormatArguments::new();
     let mut first = true;
-
     while p.token != token::Eof {
+        // parse a comma, or else report an error
         if !p.eat(exp!(Comma)) {
             if first {
                 p.clear_expected_token_types();
@@ -120,9 +111,11 @@ fn parse_args<'a>(ecx: &ExtCtxt<'a>, sp: Span, tts: TokenStream) -> PResult<'a,
             }
         }
         first = false;
+        // accept a trailing comma
         if p.token == token::Eof {
             break;
-        } // accept trailing commas
+        }
+        // parse a FormatArgument
         match p.token.ident() {
             Some((ident, _)) if p.look_ahead(1, |t| *t == token::Eq) => {
                 p.bump();
@@ -156,6 +149,10 @@ fn parse_args<'a>(ecx: &ExtCtxt<'a>, sp: Span, tts: TokenStream) -> PResult<'a,
             }
         }
     }
+
+    // Only allow implicit captures for direct literals
+    let is_direct_literal = matches!(fmtstr.kind, ExprKind::Lit(_));
+
     Ok(MacroInput { fmtstr, args, is_direct_literal })
 }