parser: add enum, union, literal, struct doc comment tests

Port tests from upstream parser_test.zig:
- "empty enum decls" (with extern/packed modifiers)
- "empty union decls" (with extern/packed/enum modifiers)
- "enum literal"
- "character literal larger than u8"
- "infix operator and then multiline string literal" (2 tests)
- "correctly space struct fields with doc comments"
- "aligned struct field"
- "comment to disable/enable zig fmt first"

Implement in parser.c:
- extern/packed modifiers before struct/union/enum in
  parsePrimaryTypeExpr

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

parser.c

@@ -469,9 +469,18 @@ static AstNodeIndex parsePrimaryTypeExpr(Parser* p) {
         exit(1);
     case TOKEN_KEYWORD_EXTERN:
     case TOKEN_KEYWORD_PACKED:
-        fprintf(stderr, "parsePrimaryTypeExpr does not support %s\n",
-            tokenizerGetTagString(tok));
-        exit(1);
+        // extern/packed can precede struct/union/enum
+        switch (p->token_tags[p->tok_i + 1]) {
+        case TOKEN_KEYWORD_STRUCT:
+        case TOKEN_KEYWORD_UNION:
+        case TOKEN_KEYWORD_ENUM:
+            p->tok_i++; // consume extern/packed
+            return parseContainerDeclAuto(p);
+        default:
+            fprintf(stderr, "parsePrimaryTypeExpr does not support %s\n",
+                tokenizerGetTagString(tok));
+            exit(1);
+        }
     case TOKEN_KEYWORD_STRUCT:
     case TOKEN_KEYWORD_OPAQUE:
     case TOKEN_KEYWORD_ENUM:

parser_test.zig

@@ -1252,3 +1252,111 @@ test "zig fmt: tagged union enum tag last token" {
         \\
     );
 }
+
+test "zig fmt: empty enum decls" {
+    try testCanonical(
+        \\const A = enum {};
+        \\const B = enum(u32) {};
+        \\const C = extern enum(c_int) {};
+        \\const D = packed enum(u8) {};
+        \\
+    );
+}
+
+test "zig fmt: empty union decls" {
+    try testCanonical(
+        \\const A = union {};
+        \\const B = union(enum) {};
+        \\const C = union(Foo) {};
+        \\const D = extern union {};
+        \\const E = packed union {};
+        \\
+    );
+}
+
+test "zig fmt: enum literal" {
+    try testCanonical(
+        \\const x = .hi;
+        \\
+    );
+}
+
+test "zig fmt: character literal larger than u8" {
+    try testCanonical(
+        \\const x = '\u{01f4a9}';
+        \\
+    );
+}
+
+test "zig fmt: infix operator and then multiline string literal" {
+    try testCanonical(
+        \\const x = "" ++
+        \\    \\ hi
+        \\;
+        \\
+    );
+}
+
+test "zig fmt: infix operator and then multiline string literal over multiple lines" {
+    try testCanonical(
+        \\const x = "" ++
+        \\    \\ hi0
+        \\    \\ hi1
+        \\    \\ hi2
+        \\;
+        \\
+    );
+}
+
+test "zig fmt: correctly space struct fields with doc comments" {
+    try testTransform(
+        \\pub const S = struct {
+        \\    /// A
+        \\    a: u8,
+        \\    /// B
+        \\    /// B (cont)
+        \\    b: u8,
+        \\
+        \\
+        \\    /// C
+        \\    c: u8,
+        \\};
+        \\
+    ,
+        \\pub const S = struct {
+        \\    /// A
+        \\    a: u8,
+        \\    /// B
+        \\    /// B (cont)
+        \\    b: u8,
+        \\
+        \\    /// C
+        \\    c: u8,
+        \\};
+        \\
+    );
+}
+
+test "zig fmt: aligned struct field" {
+    try testCanonical(
+        \\pub const S = struct {
+        \\    f: i32 align(32),
+        \\};
+        \\
+    );
+    try testCanonical(
+        \\pub const S = struct {
+        \\    f: i32 align(32) = 1,
+        \\};
+        \\
+    );
+}
+
+test "zig fmt: comment to disable/enable zig fmt first" {
+    try testCanonical(
+        \\// Test trailing comma syntax
+        \\// zig fmt: off
+        \\
+        \\const struct_trailing_comma = struct { x: i32, y: i32, };
+    );
+}