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: Expected colon (:) after object key.

       Correct syntax: { "key": value }

       Common mistakes:
       - { "key" = value } ✗ (use : not =)
       - { "key" value } ✗ (missing colon)

       Original error: expected `:`
 --> tests/ui/json/missing_colon.rs:5:28
  |
5 |     let _v = json!({ "key" "value" });
  |                            ^^^^^^^
