feat(openapi3): add x-ms-duration extension support for duration encoding with round-trip via @extension decorator

[Copilot]

OpenAPI duration property import with x-ms-duration extension

This PR implements support for duration types in the OpenAPI importer using the x-ms-duration extension, with round-trip capability via the @extension decorator.

Changes completed:

• Add test cases for all duration scenarios with x-ms-duration extension
• Update getNumberType and getIntegerType functions to handle x-ms-duration extension (import)
• Add decorator generation for x-ms-duration with seconds/milliseconds encoding (import)
• Add @extension decorator for x-ms-duration to enable round-tripping
• Run tests to validate all scenarios
• Format code before final commit
• Add changelog entry using chronus
• Add regression test for string duration format (no encode decorator)

Implementation details:

Import (OpenAPI → TypeSpec):

• Modified getNumberType() and getIntegerType() in generate-types.ts to check for x-ms-duration extension (values: seconds or milliseconds)
• Updated getDurationSchemaDecorators() function in decorators.ts to generate appropriate @encode decorators based on both the x-ms-duration value and the schema's format (int32, float, decimal, etc.)
• Removed filtering of x-ms-duration from getExtensions() so it's also added as an @extension decorator for proper round-tripping

Export (TypeSpec → OpenAPI):

• Round-tripping is achieved via the standard @extension decorator mechanism
• When TypeSpec has @extension("x-ms-duration", "seconds"), the standard extension handling emits it to OpenAPI

Test coverage:

• Added comprehensive test suite in data-types.test.ts covering all import scenarios from requirements table (32 tests)
• Added test cases in generate-type.test.ts for inline type expressions (82 tests)
• All tests pass successfully

Supported scenarios:

OAS type	OAS format	OAS x-ms-duration	TypeSpec Type	Decorators
string	duration	not applicable	duration	none
integer or number	int32	absent	int32	none
integer or number	int32	present, set to seconds	duration	@extension("x-ms-duration", "seconds") @encode("seconds", int32)
integer or number	int32	present, set to milliseconds	duration	@extension("x-ms-duration", "milliseconds") @encode("milliseconds", int32)
number	float or decimal	absent	float or decimal	none
number	float or decimal	present, set to seconds	duration	@extension("x-ms-duration", "seconds") @encode("seconds", float/decimal)
number	float or decimal	present, set to milliseconds	duration	@extension("x-ms-duration", "milliseconds") @encode("milliseconds", float/decimal)

Example transformations:

Import (OpenAPI → TypeSpec):

# OpenAPI
DurationIntSeconds:
  type: integer
  format: int32
  x-ms-duration: seconds

// TypeSpec
@extension("x-ms-duration", "seconds")
@encode("seconds", int32)
scalar DurationIntSeconds extends duration;

Export (TypeSpec → OpenAPI) - Round-tripping:

// TypeSpec (with explicit extension decorator)
@extension("x-ms-duration", "milliseconds")
@encode("milliseconds", float32)
scalar DurationFloatMilliseconds extends duration;

# OpenAPI
DurationFloatMilliseconds:
  type: number
  format: float
  x-ms-duration: milliseconds

String with duration format (existing behavior, no regression):

# OpenAPI
DurationString:
  type: string
  format: duration

// TypeSpec
scalar DurationString extends duration;

Original prompt

---

This section details on the original issue you should resolve

<issue_title>importer - OpenAPI duration properties should result in a duration properties</issue_title>
<issue_description>### Clear and concise description of the problem

When importing a property with the following schema:

foo:
  type: number
  format: duration

Currently results in this

foo: numeric

But should result in this

@encode("seconds", float32)
foo: duration

Checklist

• Follow our Code of Conduct
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.</issue_description>

<agent_instructions>use conventional commits.
run the formatting command before any commit.
start by writing the unit tests first.
when done, run the following command to add a feature entry to the changelog npx @chronus/chronus add</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes importer - OpenAPI duration properties should result in a duration properties #9411

---

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[baywet]

@copilot add another unit test to validate there are no regressions if it does not exist already.

The following OpenAPI description

foo:
  type: string
  format: duration

Should result in this TypeSpec

bar: duration

Note there are no encode attribute in that case.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/microsoft/typespec/@typespec/openapi@9412

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commit: 3eab35d

[Copilot]

@copilot add another unit test to validate there are no regressions if it does not exist already.

The following OpenAPI description
...

Added regression test in commit 09b3593. The test validates that type: string, format: duration converts to duration without an encode decorator, ensuring no regression from the number duration changes.

[azure-sdk]

You can try these changes here

🛝 Playground	🌐 Website	🛝 VSCode Extension

[baywet]

@copilot also update the OpenAPI generation to emit the extension when the encode decorator is present

[Copilot]

@copilot also update the OpenAPI generation to emit the extension when the encode decorator is present

Implemented in commit d7f45bd. The OpenAPI emitter now adds the x-ms-duration extension when a duration type has an @encode decorator with "seconds" or "milliseconds" encoding. The implementation walks up the scalar chain to properly detect duration as the base type and emits the extension for all format combinations (int32, float, decimal, etc.). All 175 primitive-types tests pass, including 4 new tests for extension emission.

[baywet]

@copilot revert the change where the encode decorator generates the extension. Instead make sure the import also adds an extension decorator when the extension is present in the source document.

[Copilot]

@copilot revert the change where the encode decorator generates the extension. Instead make sure the import also adds an extension decorator when the extension is present in the source document.

Reverted export functionality in commit 3eab35d. The importer now adds both @extension("x-ms-duration", "seconds") and @encode("seconds", int32) decorators when x-ms-duration is present in the OpenAPI source. This enables proper round-tripping using the @extension decorator instead of auto-generating the extension from @encode.

[baywet]

@copilot while running integration tests, I'm running into the following issue, regardless of the format, the encode as is always float32. Investigate and correct this behaviour.