[EloB]

Description

AccessorNamesTypeAttributeKind and EnumValuesTypeAttributeKind get a
combine. Before this, both used the base class's, which panics with
Cannot combine type attribute ….

• Accessor names (attributes/AccessorNames.ts): the result keeps every
  entry the combined copies agree on, and drops a name for which they
  have different entries, so that name falls back to its default name.
  Names that only one copy gives are kept.
• Enum values (attributes/EnumValues.ts): copies that are all the same
  are combined. Any other combination fails as before, with the same
  message.

A test commit adds test/inputs/schema/accessors-enum-union.schema. It
has the same enum twice, once as a definition with qt-accessors and once
inline in a nullable union, which is what the TypeScript input makes of
f: E | null for a string enum. It comes with two samples and one
expected failure ("f": "c"). The commit also adds a unit test,
test/unit/enum-values-combine.test.ts: two definitions with identical
qt-enum-values combine (_A = 0,, _B = 1, in C), and two that differ
still fail with Cannot combine type attribute enumValues.

Related Issue

Fixes #3551

Motivation and Context

The TypeScript input gives each string enum's definition its member names
as qt-accessors. When the same enum also appears in a union
(E | null, E[] | F, an optional E in Python), or two enums have the
same cases, the types become one and their attributes are combined, and
quicktype stopped with Internal error: Cannot combine type attribute accessorNames.
JSON Schema definitions of the same enum with qt-accessors or
qt-enum-values failed the same way.

Why these semantics:

• The common case is the same enum meeting itself with identical entries,
  so its member names are kept. f: E | null names the cases as f: E
  does.
• When two copies give different names for the same value, neither is
  more right than the other. Dropping the name gives the result the
  string-literal alias form (type E = "a" | "b") gives, and the result
  does not depend on the order in which types are combined. Keeping the
  first or the last entry would depend on it.
• Enum values cannot drop an entry the same way. A value is part of what
  the enum means, and dropping one can give two cases the same value.
  With copies {"a": "0", "b": "1"} and {"a": "1", "b": "1"}, dropping
  a gives C F_A = 1, F_B = 1 (the first case defaults to 1), and the
  duplicate case labels do not compile.

Previous Behaviour / Output

$ quicktype --src-lang typescript --lang cs e.ts
Error: Internal error: Cannot combine type attribute accessorNames.

with e.ts:

export enum E { A = "a", B = "b" }
export interface X { f: E | null }

New Behaviour / Output

The code is generated. For these four declarations, the output is
byte-for-byte the same as for the same declarations written with string-literal
aliases, in C#, Python, Go and TypeScript:

• f: E | null
• f: E[] | F
• e: E; f: F, where F has the same cases as E
• f?: E; g?: E

For the JSON Schema example with two definitions whose qt-accessors are
{a: Alpha, b: Beta} and {a: Alpha, b: Other}, the C# enum is
{ Alpha, B }. Two definitions with identical qt-enum-values now work.
Definitions whose qt-enum-values differ still fail with
Cannot combine type attribute enumValues.

No output of the repository's existing inputs changes, since combining
these attributes always failed before.

How Has This Been Tested?

Environment: macOS 26.6 (arm64), Node 24.16.0, Python 3.12.16 with
mypy 2.4.1, OpenJDK 21.0.11 with Maven 3.10.0, Ruby 4.0.6, Apple clang 21
(C, C++, Objective-C), Swift, Rust (cargo) and Dart.

On this branch:

• npm ci, npm run build, npm run lint (passes), npm run test:unit
  (55 files, 243 tests pass).
• QUICKTEST=true FIXTURE=schema-typescript,schema-javascript,schema-python,schema-cjson,schema-ruby,schema-java npm run test:fixtures -- test/inputs/schema/accessors-enum-union.schema:
  all 6 pass.
• The same input with schema-swift, schema-rust, schema-dart,
  schema-typescript-zod, schema-typescript-effect-schema, schema-flow,
  schema-javascript-prop-types, schema-java-datetime-legacy,
  schema-objective-c and schema-cplusplus: all 10 pass.
• The TypeScript-input cases above: quicktype exits with 0 for every
  --lang except objc, which fails with
  Internal error: Cannot repeat a string a negative number of times.
  The string-literal alias form fails the same way on master, so that is
  a separate problem.

With only the test commit (the fix not applied):

• schema-typescript (and the others) fail on accessors-enum-union.schema
  with Internal error: Cannot combine type attribute accessorNames.
• The unit test fails on the identical-values case.

Not run here, because the toolchains are not installed: C#, Go, Kotlin,
Scala, Elm, PHP, Elixir, Haskell, Crystal and Pike.

Screenshots (if appropriate):

n/a

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Written by Claude (an AI assistant made by Anthropic) and posted on behalf of the account owner (EloB). The reproduction, fix and tests were checked by running them as described above.

🤖 Generated with Claude Code