fix(rendering): preserve enum case source order

[schani]

The bug

Enum cases were always rendered in alphabetical order, regardless of the
order they appear in the source JSON Schema (or JSON samples). For example:

$ cat day.schema.json
{"$schema":"http://json-schema.org/draft-07/schema#","type":"string","enum":["Monday","Tuesday","Friday","Sunday"]}

$ quicktype --lang csharp --src-lang schema day.schema.json
public enum DaySchemaEnum { Friday, Monday, Sunday, Tuesday };

instead of the expected declaration order Monday, Tuesday, Friday, Sunday.
This affected every generated language (~29 renderers), since they all share
the same code path. While JSON round-tripping still worked (because
(de)serializers match by string name), anything relying on positional/ordinal
semantics — e.g. C#'s implicit underlying int enum values — broke, along
with unnecessary diff noise whenever a schema's enum order changed.

Root cause

ConvenienceRenderer.forEachEnumCase in
packages/quicktype-core/src/ConvenienceRenderer.ts unconditionally ran the
already source-ordered case names through mapSortBy, alphabetizing them
before rendering. A second, related spot in
packages/quicktype-core/src/MakeTransformations.ts (makeEnumTransformer)
also alphabetically sorted enumType.cases before building the enum's
runtime string-match transformer (used e.g. by the TypeScript/Flow "Convert"
helpers), for the same reason.

The fix

Removed both forced alphabetical sorts, since EnumType.cases (and the
derived case-name map) already preserve the source's insertion order:

• ConvenienceRenderer.forEachEnumCase now iterates caseNames directly
  instead of calling mapSortBy on it.
• MakeTransformations.makeEnumTransformer now maps over
  Array.from(enumType.cases) directly instead of sorting it first.

This is a default-behavior fix (no new renderer option), consistent with
other breaking-default fixes already sanctioned for the next major release.

Test coverage

• Added test/unit/enum-order.test.ts, a focused regression test that
  reproduces the exact issue Enums are ALWAYS sorted #2401 repro via the quicktype API and asserts
  the generated C# enum preserves declaration order
  (Monday, Tuesday, Friday, Sunday). This test fails on unfixed code and
  passes with the fix.
• Extended the C# fixture driver (test/fixtures/csharp/Program.cs) to
  assert, when running the existing test/inputs/schema/enum.schema +
  enum.1.json fixture sample, that the generated QuickType.cs contains
  public enum Lvc { Lawful, Neutral, Chaotic }; (the schema's declared
  ["lawful", "neutral", "chaotic"] order, which is not alphabetical) rather
  than a sorted order. This exercises the fix through the existing
  schema-csharp fixture pipeline without needing new schema/sample files.

Verification performed locally

• npm run build passes.
• npm run test:unit: all 177 unit tests pass, including the new
  enum-order.test.ts.
• Manually re-ran the original repro for C#, TypeScript, Python, Go, Java,
  Kotlin, Swift, and Rust — all now emit enum cases in source declaration
  order.
• The dotnet toolchain is not available in this environment, so the full
  schema-csharp end-to-end fixture (which exercises the new
  Program.cs assertion) could not be executed locally; it will be
  validated by CI.

Fixes #2401.

🤖 Generated with Claude Code

[schani]

Wow, this is a super shitty way of testing! The fixture should not be special-cased for specific test cases! Find a principled way of doing this!

[schani]

Agreed, that was the wrong place for it. I removed the filename-keyed check from the C# fixture driver in dfa4681.

The fixture harness is a JSON round-trip (deserialize, reserialize, compare), and enum case source ordering is invisible to a string round-trip, so a fixture genuinely can't express this behavior. That ordering is instead asserted directly and portably in test/unit/enum-order.test.ts, which checks the generated C# and C++ enum declarations preserve schema order through the quicktype API. The fixture driver is back to its original form with no special cases.