error: Invalid JSON object syntax.
       Expected: { "key": value, ... }

       Common mistakes:
       - Keys must be string literals: { "name": "Alice" } ✓ not { name: "Alice" } ✗
       - Use colon (:) between key and value: { "x": 1 } ✓ not { "x" = 1 } ✗
       - Separate pairs with commas: { "a": 1, "b": 2 } ✓

       Original error: Invalid object key.
       Expected: string literal

       Correct syntax:
       - { "name": "Alice" } ✓
       - { "age": 30 } ✓

       Common mistakes:
       - { name: "Alice" } ✗ (missing quotes around key)
       - { 'name': "Alice" } ✗ (use double quotes, not single)

       Original error: expected string literal
 --> tests/ui/json/invalid_key.rs:5:22
  |
5 |     let _v = json!({ 123: "value" });
  |                      ^^^
