feat: Make model property generation deterministic by sorting alphabetically

[scarf005]

Summary

added SORT_MODEL_PROPERTIES rule to the OpenAPI Normalizer that sorts schema properties alphabetically by name. This ensures deterministic code generation output regardless of property ordering in the source spec, preventing unnecessary diffs like:

-    'paged'?: boolean;
     'unpaged'?: boolean;
+    'paged'?: boolean;

this PR was generated by claude opus 4.5

Changes

1. OpenAPINormalizer.java: Added new SORT_MODEL_PROPERTIES rule that:

   • Uses TreeMap to sort properties by natural string order
   • Applies at the OpenAPI normalization stage, working for all generators
   • Is opt-in (defaults to false) to maintain backward compatibility

2. docs/customization.md: Added documentation for the new rule

3. OpenAPINormalizerTest.java: Added tests for:

   • Verifying properties are sorted when rule is enabled
   • Verifying properties retain original order when rule is disabled (default)

Usage

openapi-generator generate \
  -g java \
  -i petstore.yaml \
  -o /tmp/java-client/ \
  --openapi-normalizer SORT_MODEL_PROPERTIES=true

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[wing328]

thanks for the PR

what about adding this functionality in openapi normalizer via a new rule (e.g. SORT_MODEL_PROPOERTIES) so that this will work with all generators?

a good starting point is https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java#L883 (update the method signature to accept schema instead of schema.getProperties())

[scarf005]

alright, will do. would this be okay to enable SORT_MODEL_PROPOERTIES by default?

[wing328]

alright, will do. would this be okay to enable SORT_MODEL_PROPOERTIES by default?

I prefer not to at this stage as this will "change" the output for all generators.

generally we advise the users to put the properties in whatever order they prefer in the source (openapi spec) instead.

[wing328]

please update the doc as well: https://github.com/OpenAPITools/openapi-generator/blob/master/docs/customization.md#openapi-normalizer

[wing328]

for new rules, we also prefer a test or 2 in https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/test/java/org/openapitools/codegen/OpenAPINormalizerTest.java

let me know if you need help adding tests 🙏

[scarf005]

applied requested changes and force pushed; lemme know if something looks off!

[wing328]

looks good at the first glance 👍

to confirm, you did test this locally with your use cases and it works as expected, right?

[cubic-dev-ai]

No issues found across 3 files

[scarf005]

looks good at the first glance 👍

to confirm, you did test this locally with your use cases and it works as expected, right?

checked locally, typescript-axios seems to work well

Details

Before

After

[wing328]

did some tests locally and the result works as expected