[python] Fix enum member names corrupted by YAML 1.1/1.2 boundary

[msyyc]

fix #11138

Problem

For a date-like TypeSpec label such as:

union ApiVersion {
  string;
  `2020-01-01`: "2020-01-01";
}

the emitter's enumName() correctly computes the enum member name as the string 2020_01_01. However, the code model is serialized with js-yaml (YAML 1.2), which dumps this scalar unquoted (name: 2020_01_01). The Python generator then parses the YAML with PyYAML (YAML 1.1), where 2020_01_01 is a valid integer separator syntax, so the name is read back as the integer 20200101 — corrupting the enum member name.

This is the underlying root cause behind #11143. That PR worked around the crash in pygen by reconstructing the name from the enum value via regex, rather than fixing the corruption at the source.

Fix

Emitter (root cause) — force-quote string scalars when serializing the code model so every string round-trips faithfully through PyYAML:

• Added a shared dumpCodeModelToYaml() helper (forceQuotes: true, quotingType: '"') in external-process.ts, used by both the node and pyodide serialization paths.

pygen (defensive) — simplified enum value name handling to a plain str() coercion so the generator stays robust to any scalar, letting the existing digit → ENUM_ prefixing produce ENUM_2020_01_01.

Tests

• New emitter unit test (emitter/test/external-process.test.ts) asserting ambiguous scalars are quoted and round-trip as strings.
• Updated pygen unit tests covering both the happy path (string 2021_01_01 → ENUM_2021_01_01) and the defensive fallback (int 20210101 → ENUM_20210101).

Verified end-to-end: emitter dump → PyYAML load now yields the string '2020_01_01' (previously int 20200101). Emitter vitest (4 passed) and pygen pytest (16 passed) green.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/http-client-python@11162

commit: 6665a32

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-client-python

Show changes

@typespec/http-client-python - fix ✏️

Fix enum member names derived from date-like TypeSpec labels (e.g. `2020-01-01`) being corrupted by the js-yaml (YAML 1.2) to PyYAML (YAML 1.1) boundary. String scalars are now force-quoted when serializing the code model so names such as 2020_01_01 round-trip as strings instead of being read back as integers

[azure-sdk-automation]

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[timotheeguerin]

just wondering here do you actually even need yaml can't you serialize as json, would be faster and less deps

[timotheeguerin]

i feel like yaml is not a great format for data serialization better suited for config