[fine] Many test improvements, error improvements

- Check for more error conditions
- Move to more definitive error assertions
- Simpler error messages in some cases
- Test more conditions more thoroughly, revisit old tests

fine/src/parser.rs

@@ -510,7 +510,6 @@ fn file(p: &mut CParser) {
     let m = p.start();
     while !p.eof() {
         match p.peek() {
-            TokenKind::Fun => function(p),
             TokenKind::Class => class(p),
             _ => statement(p),
         }
@@ -660,6 +659,7 @@ fn block(p: &mut CParser) {
 
 fn statement(p: &mut CParser) {
     match p.peek() {
+        TokenKind::Fun => function(p),
         TokenKind::LeftBrace => block(p),
         TokenKind::Let => statement_let(p),
         TokenKind::Return => statement_return(p),
@@ -988,11 +988,14 @@ mod tests {
     #[test]
     fn tree_ref_size() {
         // What's the point of doing all that work if the tree ref isn't nice
-        // and "small"?
+        // and "small"? TreeRef is pervasive throughout the system: we use
+        // them to key function definitions and the type checker and use them
+        // to link classes to their definitions, etc. It's important that an
+        // Option<TreeRef> be *extremely* cheap to manipulate.
         //
-        // TODO: This is a dumb optimization because tokens are
+        // TODO: This optimization isn't as good as it might be because tokens are
         //       huge so Child is huge no matter what we do. If we retain
-        //       tokens out of line then we can re-visit this optimization.
+        //       tokens out of line then we can take full advantage of this.
         assert_eq!(4, std::mem::size_of::<Option<TreeRef>>());
     }
 }