fix(InlineModelResolver): do not merge untitled inline schemas differing only by description (#24004)

[seonwooj0810]

Fixes #24004

Problem

A schema with two structurally-identical inline (untitled) object properties that differ only in their descriptions is generated differently in 7.22 vs 7.23. Given:

"properties": {
  "abc": { "type": "object", "description": "first container",
           "properties": { "result": { "type": "string", "description": "ABC Result" } } },
  "def": { "type": "object", "description": "second container",
           "properties": { "result": { "type": "string", "description": "DEF Result" } } }
}

• 7.22 generates two distinct types — abc → …Abc, def → …Def.
• 7.23 generates def with type …Abc, so code expecting …Def no longer compiles.

Root cause

The structural-signature dedup fallback introduced in #23856 (to prevent numbered duplicate models from multi-file OAS 3.1 specs) serialises schemas with description/type/example stripped at every level and was consulted/registered for all schemas in matchGenerated()/addGenerated(). Once those volatile fields are stripped, abc and def produce an identical signature, so def is unified with abc.

That fallback is only appropriate for titled named types (which should be reused wherever they appear, despite parser-induced volatility). Anonymous/untitled inline schemas may be intentionally distinct — exactly as the existing titled-only guards in flatten() pre-population and deduplicateComponents() already note ("anonymous schemas may be intentionally distinct").

Fix

Restrict the structural-signature fallback (both lookup in matchGenerated() and registration in addGenerated()) to schemas with a non-null title. Exact-signature matching is unchanged, so genuine duplicates are still reused, and the #23856 multi-file dedup behaviour (which operates on titled schemas) is preserved.

Test evidence

Added InlineModelResolverTest#resolveInlineModelKeepsUntitledSchemasDifferingOnlyByDescriptionDistinct, which reproduces the issue and asserts abc/def resolve to distinct $refs. Verified it fails on master and passes with this change.

Full InlineModelResolverTest suite (including the #23856 structural-dedup regression tests …MutatesPropertyDescriptions, …MutatesPropertyTypes, and the multi-file root.yaml cases) passes:

Tests run: 56, Failures: 0, Errors: 0, Skipped: 0

Verification done: built/tested on JDK 21 via ./mvnw -pl modules/openapi-generator -am test -Dtest=InlineModelResolverTest.

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore samples — N/A: this change does not alter generated output for any existing sample (no committed sample uses two untitled inline schemas differing only by description); full InlineModelResolverTest passes unchanged.
• Filed the PR against the correct branch: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

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Summary by cubic

Prevent merging of untitled inline schemas that differ only by description, restoring distinct generated types and fixing a 7.23 regression. Structural-signature dedup now applies only to titled schemas; named types are still reused as expected.

• Bug Fixes
  • Limit structural-signature fallback to titled schemas in InlineModelResolver (matchGenerated() and addGenerated()).
  • Keep exact-signature dedup unchanged for true duplicates.
  • Add regression test to ensure abc/def inline objects resolve to distinct $refs.
  • Preserve multi-file OAS 3.1 reuse behavior for titled schemas.

^{Written for commit a30b402. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}