parser: add block, break, grouped expression, array type tests

Port tests from upstream parser_test.zig:
- "allow empty line before comment at start of block"
- "comptime struct field"
- "break from block"
- "grouped expressions (parentheses)"
- "array types last token"

Fix bugs in parser.c:
- parseBreakLabel: use null_token instead of null_node
- test decl: use null_token for unnamed tests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

parser.c

@@ -982,8 +982,8 @@ static AstNodeIndex parseVarDeclProto(Parser* p) {
 }
 
 static AstTokenIndex parseBreakLabel(Parser* p) {
-    if (eatToken(p, TOKEN_COLON) == null_node)
-        return null_node;
+    if (eatToken(p, TOKEN_COLON) == null_token)
+        return null_token;
     return expectToken(p, TOKEN_IDENTIFIER);
 }
 
@@ -1609,7 +1609,7 @@ static Members parseContainerMembers(Parser* p) {
                 = (p->token_tags[p->tok_i] == TOKEN_STRING_LITERAL
                       || p->token_tags[p->tok_i] == TOKEN_IDENTIFIER)
                 ? nextToken(p)
-                : 0;
+                : null_token;
             const AstNodeIndex body = parseBlock(p);
             assert(body != 0);
             const AstNodeIndex test_decl = addNode(&p->nodes,

parser_test.zig

@@ -873,3 +873,62 @@ test "zig fmt: remove empty lines at start/end of container decl" {
         \\
     );
 }
+
+test "zig fmt: allow empty line before comment at start of block" {
+    try testCanonical(
+        \\test {
+        \\
+        \\    // foo
+        \\    const x = 42;
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: comptime struct field" {
+    try testCanonical(
+        \\const Foo = struct {
+        \\    a: i32,
+        \\    comptime b: i32 = 1234,
+        \\};
+        \\
+    );
+}
+
+test "zig fmt: break from block" {
+    try testCanonical(
+        \\const a = blk: {
+        \\    break :blk 42;
+        \\};
+        \\const b = blk: {
+        \\    break :blk;
+        \\};
+        \\const c = {
+        \\    break 42;
+        \\};
+        \\const d = {
+        \\    break;
+        \\};
+        \\
+    );
+}
+
+test "zig fmt: grouped expressions (parentheses)" {
+    try testCanonical(
+        \\const r = (x + y) * (a + b);
+        \\
+    );
+}
+
+test "zig fmt: array types last token" {
+    try testCanonical(
+        \\test {
+        \\    const x = [40]u32;
+        \\}
+        \\
+        \\test {
+        \\    const x = [40:0]u32;
+        \\}
+        \\
+    );
+}