Potential JSON serialization regression in 1.18.0

[amy-keibler]

What happened?

Thanks for developing such a useful snapshot testing library. I'm using it in a CycloneDX SBOM library. I received a dependabot PR to bump the version to the 1.18.0 version, but that had failing tests. When I investigated, I noticed that the JSON serialization output regressed, causing tests to fail. I assume it's related to the dependency changes and is likely caused by a bug in an upstream library, but I figured I should bring it to your attention, given its impact on the snapshot output.

The short description is that it seems like pretty-printed JSON is sometimes moved to the same line as the opening {, as shown in the snapshot output for the reproduction repository

❯ less src/snapshots/example_insta_regression__tests__serializes_to_json_correctly.snap.new 
---
source: src/lib.rs
assertion_line: 22
expression: "vec![Example :: ChoiceA(ChoiceAStruct { field_a : \"a\".to_string() }), Example\n    :: ChoiceB(\"b\".to_string()),]"
---
[
  {"choiceA": {
      "fieldA": "a"
    }
  },
  {"choiceB": "b"
  }
]

Reproduction steps

I created an example repository to demonstrate the issue. There is a PR open amy-keibler/example-insta-regression#1 with failing tests that demonstrate the issue in CI

1. Clone the linked repository
   • Observe that that the version of insta is ~1.17.1 in the main branch
2. Run tests via cargo test and observe that they are passing
3. Checkout the dependency-upgrade branch
   • Observe that the version of insta is 1.18.0
4. Run tests via cargo test and observe that they are failing with the following output

   ...
   -old snapshot
   +new results
   ────────────┬───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       0     0 │ [
       1       │-  {
       2       │-    "choiceA": {
             1 │+  {"choiceA": {
       3     2 │       "fieldA": "a"
       4     3 │     }
       5     4 │   },
       6       │-  {
       7       │-    "choiceB": "b"
             5 │+  {"choiceB": "b"
       8     6 │   }
       9     7 │ ]
   ────────────┴───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   
   ...
   

Insta Version

1.18.0

rustc Version

No response

What did you expect?

No response

[mitsuhiko]

This is indeed a regression with newtype structs. Thanks for the report. I will prepare a bugfix release for this.

[mitsuhiko]

Pushed out 1.18.1 which fixes this. Thanks for the report!