[fine] Fix a problem with a stuck parser

Whoops

fine/src/parser.rs

@@ -361,7 +361,7 @@ impl<'a> CParser<'a> {
 
     fn advance(&mut self) {
         assert!(!self.eof()); // Don't try to advance past EOF
-        self.fuel.set(256); // Consuming a token, rest stuck detector
+        self.fuel.set(256); // Consuming a token, reset stuck detector
         self.events.push(ParseEvent::Advance {
             token: self.current.clone(),
         });
@@ -381,11 +381,20 @@ impl<'a> CParser<'a> {
     }
 
     fn peek(&self) -> TokenKind {
-        assert!(self.fuel.get() > 0, "parser is stuck!");
+        if self.fuel.get() == 0 {
+            panic!(
+                "parser is stuck at '{}' ({})!",
+                self.current, self.current.start
+            );
+        }
         self.fuel.set(self.fuel.get() - 1);
         self.current.kind
     }
 
+    // fn trace(&self, msg: &str) {
+    //     eprintln!("{}: {}: {}", self.current.start, self.current, msg);
+    // }
+
     fn at(&self, kind: TokenKind) -> bool {
         self.peek() == kind
     }
@@ -511,6 +520,14 @@ fn file(p: &mut CParser) {
     while !p.eof() {
         match p.peek() {
             TokenKind::Class => class(p),
+            TokenKind::RightBrace => {
+                // An error parsing mismatched braces can leave me at an
+                // un-balanced right brace, which unfortunately will not be
+                // consumed by the statement below. (Statement currently
+                // falls through to expression_statement, which checks for
+                // the right-brace that a block would end with.)
+                p.advance_with_error("unbalanced '}'");
+            }
             _ => statement(p),
         }
     }
@@ -542,7 +559,11 @@ fn class(p: &mut CParser) {
     p.expect(TokenKind::Identifier, "expected a class name");
     if p.eat(TokenKind::LeftBrace) {
         while !p.at(TokenKind::RightBrace) && !p.eof() {
-            field_decl(p);
+            if p.at(TokenKind::Identifier) {
+                field_decl(p);
+            } else {
+                p.advance_with_error("expected a field declaration");
+            }
         }
     }
     p.expect(TokenKind::RightBrace, "expected a class to end with a '}'");

fine/tests/errors/unbalanced_right_brace.fine

@@ -0,0 +1,20 @@
+fun foo() { }
+
+} // <- Whoopsie!
+
+// @concrete:
+// | File
+// |   FunctionDecl
+// |     Fun:'"fun"'
+// |     Identifier:'"foo"'
+// |     ParamList
+// |       LeftParen:'"("'
+// |       RightParen:'")"'
+// |     Block
+// |       LeftBrace:'"{"'
+// |       RightBrace:'"}"'
+// |   Error
+// |     Error:'"Error at '}': unbalanced '}'"'
+// |     RightBrace:'"}"'
+// |
+//