[fine] Don't panic on this parse error

fine/src/parser.rs

@@ -430,7 +430,7 @@ impl<'a> CParser<'a> {
     }
 
     fn expect_start(&mut self, kind: TokenKind) {
-        assert!(self.eat(kind));
+        assert!(self.eat(kind), "should have started with {kind:?}");
     }
 
     fn advance_with_error<T>(&mut self, error: T) -> MarkClosed
@@ -708,7 +708,7 @@ fn block(p: &mut CParser) {
     while !p.at(TokenKind::RightBrace) && !p.eof() {
         statement(p);
     }
-    p.expect(TokenKind::RightBrace, "expect '}' to start a block");
+    p.expect(TokenKind::RightBrace, "expect '}' to end a block");
 
     p.end(m, TreeKind::Block);
 }
@@ -756,6 +756,7 @@ fn statement_return(p: &mut CParser) {
     let m = p.start();
 
     p.expect_start(TokenKind::Return);
+    // TODO: Make expression optional if we're returning ()
     expression(p);
     if !p.at(TokenKind::RightBrace) {
         p.expect(TokenKind::Semicolon, "expect ';' to end a return statement");
@@ -938,13 +939,19 @@ fn conditional(p: &mut CParser) -> MarkClosed {
 
     p.expect_start(TokenKind::If);
     expression(p);
-    block(p);
+    if p.at(TokenKind::LeftBrace) {
+        block(p)
+    } else {
+        p.error("expected a block after `if`")
+    }
     if p.eat(TokenKind::Else) {
         if p.at(TokenKind::If) {
             // Don't require another block, just jump right into the conditional.
             conditional(p);
-        } else {
+        } else if p.at(TokenKind::LeftBrace) {
             block(p);
+        } else {
+            p.error("expected a block after `else`")
         }
     }
 

fine/tests/expression/errors/broken_conditional.fine

@@ -0,0 +1,8 @@
+fun test() {
+  if true true { }
+}
+
+// NOTE: These errors should be better
+// @expect-errors:
+// | 2:10: Error at 'true': expected a block after `if`
+// | 2:15: Error at '{': expect ';' to end an expression statement