parser: add zig fmt on/off and slice operator tests

Port tests from upstream parser_test.zig:
- "comment to disable/enable zig fmt"
- "line comment following 'zig fmt: off'"
- "doc comment following 'zig fmt: off'"
- "alternating 'zig fmt: off' and 'zig fmt: on'"
- "spaces around slice operator"

Fix parsePrimaryTypeExpr: don't reject identifier followed by colon;
the colon may be part of slice sentinel syntax, not a label.

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

parser.c

@@ -509,12 +509,6 @@ static AstNodeIndex parsePrimaryTypeExpr(Parser* p) {
             });
     }
     case TOKEN_IDENTIFIER:
-        if (p->token_tags[p->tok_i + 1] == TOKEN_COLON) {
-            fprintf(stderr,
-                "parsePrimaryTypeExpr does not support identifier followed by "
-                "colon\n");
-            exit(1);
-        }
         return addNode(&p->nodes,
             (AstNodeItem) {
                 .tag = AST_NODE_IDENTIFIER,

parser_test.zig

@@ -1432,3 +1432,67 @@ test "zig fmt: builtin call with trailing comma" {
         \\
     );
 }
+
+test "zig fmt: comment to disable/enable zig fmt" {
+    try testTransform(
+        \\const  a  =  b;
+        \\// zig fmt: off
+        \\const  c  =  d;
+        \\// zig fmt: on
+        \\const  e  =  f;
+    ,
+        \\const a = b;
+        \\// zig fmt: off
+        \\const  c  =  d;
+        \\// zig fmt: on
+        \\const e = f;
+        \\
+    );
+}
+
+test "zig fmt: line comment following 'zig fmt: off'" {
+    try testCanonical(
+        \\// zig fmt: off
+        \\// Test
+        \\const  e  =  f;
+    );
+}
+
+test "zig fmt: doc comment following 'zig fmt: off'" {
+    try testCanonical(
+        \\// zig fmt: off
+        \\/// test
+        \\const  e  =  f;
+    );
+}
+
+test "zig fmt: alternating 'zig fmt: off' and 'zig fmt: on'" {
+    try testCanonical(
+        \\// zig fmt: off
+        \\// zig fmt: on
+        \\// zig fmt: off
+        \\const  e  =  f;
+        \\// zig fmt: off
+        \\// zig fmt: on
+        \\// zig fmt: off
+        \\const  a  =  b;
+        \\// zig fmt: on
+        \\const c = d;
+        \\// zig fmt: on
+        \\
+    );
+}
+
+test "zig fmt: spaces around slice operator" {
+    try testCanonical(
+        \\var a = b[c..d];
+        \\var a = b[c..d :0];
+        \\var a = b[c + 1 .. d];
+        \\var a = b[c + 1 ..];
+        \\var a = b[c .. d + 1];
+        \\var a = b[c .. d + 1 :0];
+        \\var a = b[c.a..d.e];
+        \\var a = b[c.a..d.e :0];
+        \\
+    );
+}