[fine] Improve wildcard parsing, fix ephemera bug with peek_next

fine/src/parser.rs

@@ -343,9 +343,17 @@ impl<'a> CParser<'a> {
             events: Vec::new(),
             panic: false,
         };
-        parser.current = parser.tokens.next();
-        parser.next = parser.tokens.next();
-        parser.skip_ephemera();
+
+        // Getting started: put the first token into `next` and then fast
+        // forward past ephemera to the first "real" token.
+        parser.next_real_token();
+
+        // Put `next` into `current`.
+        std::mem::swap(&mut parser.current, &mut parser.next);
+
+        // Now set `next` to the *next* real token.
+        parser.next_real_token();
+
         parser
     }
 
@@ -385,15 +393,12 @@ impl<'a> CParser<'a> {
         });
         // Move next into current (and current into next but who cares, thanks rust.)
         std::mem::swap(&mut self.current, &mut self.next);
-        self.next = self.tokens.next();
-        self.skip_ephemera();
+        self.next_real_token();
     }
 
-    fn skip_ephemera(&mut self) {
-        while self.current.kind == TokenKind::Whitespace || self.current.kind == TokenKind::Comment
-        {
-            // Move next into current (and current into next but who cares, thanks rust.)
-            std::mem::swap(&mut self.current, &mut self.next);
+    fn next_real_token(&mut self) {
+        self.next = self.tokens.next();
+        while self.next.kind == TokenKind::Whitespace || self.next.kind == TokenKind::Comment {
             self.next = self.tokens.next();
         }
     }
@@ -991,6 +996,8 @@ fn is_expression(p: &mut CParser, left: MarkClosed, right_power: u8) -> MarkClos
     p.end(m, TreeKind::IsExpression)
 }
 
+const PATTERN_START: &[TokenKind] = &[TokenKind::Identifier, TokenKind::Underscore];
+
 fn pattern(p: &mut CParser, right_power: u8) {
     let m = p.start();
 
@@ -1260,7 +1267,7 @@ fn match_body(p: &mut CParser) {
 
     p.expect_start(TokenKind::LeftBrace);
     while !p.at(TokenKind::RightBrace) && !p.eof() {
-        if p.at(TokenKind::Identifier) {
+        if p.at_any(PATTERN_START) {
             // TODO: type_expr_first ?
             match_arm(p);
         } else {