Let scalar to CLR type mapping be overridden from a settings file

[joadan]

What

The generator mapped GraphQL scalars to CLR types through a hardcoded table with no way for a user to influence it. A schema whose DateTime you want as DateTime rather than DateTimeOffset, or whose BigInt you want as long rather than a generated CustomScalar wrapper, had no recourse.

This adds a json settings file that carries every existing option plus a scalarMappings table:

{
  "endpoint": "https://api.example.com/graphql",
  "client": "MyClient",
  "namespace": "My.Ns",
  "scalarMappings": {
    "DateTime": "System.DateTime",
    "BigInt":   "long",
    "Json":     null
  }
}

Linq2GraphQL                                                 # picks up ./linq2graphql.json
Linq2GraphQL --config settings.json
Linq2GraphQL --config settings.json -o="SomewhereElse"       # flag wins
Linq2GraphQL https://api/graphql -c=Client                   # unchanged

Three mapping behaviours:

• Mapping a scalar to a simple type emits that type and suppresses its generated CustomScalar class.
• Mapping an already-mapped scalar changes the emitted type.
• Mapping to null opts a built-in scalar out, generating a CustomScalar for it instead.

How

The mapping table moves off a static Helpers.TypeMapping onto GeneratorSettings.Current, copied fresh per run so overrides cannot leak between runs. Its two consumers read it through Helpers.EffectiveTypeMapping: BaseType.GetCoreType for the emitted type name, and Schema.GetCustomScalars, which treats absence from the table as "generate a CustomScalar for this scalar" — which is why one setting drives both halves.

Targets validate against an allow-list of simple BCL types rather than accepting any string. CoreType.CSharpType is not decorative — it drives UseSharpNoneNull and InputFactoryClassTemplate — and a target that does not resolve to a real Type leaves it null, which silently emits the wrong nullability and the wrong input factory overload instead of failing. Bad targets now fail the run with the supported list in the message.

Unknown top-level settings are also an error: System.Text.Json drops unmapped members silently, so the singular "scalarMapping" would otherwise produce a client with none of the mappings applied and no indication why.

Compatibility

Flag-only invocations behave exactly as before, including scripts/regenerate-test-clients.ps1. An explicitly passed option always wins over the file. The checked-in test clients are unchanged.

One sharp edge worth knowing: scalarMappings has no command line equivalent, so it is the one setting a discovered linq2graphql.json supplies that cannot be overridden back off from the command line. The generator prints the path of the file it read, so a picked-up file is visible rather than silent. If that turns out to matter, the answer is a --no-config flag.

Also here

regenerate-test-clients.ps1 -Check reported drift on Windows for clients that had not drifted. It used git status, which compares the bytes on disk: the generator always writes LF while .gitattributes text=auto gives a CRLF working tree, so every regenerated file came back modified. It now uses git diff, which applies the same normalization git applies on checkin, paired with git ls-files --others to keep catching a newly generated file. Pre-existing, unrelated to the feature, but it would have made CI on Windows unusable.

The docs site option list had also fallen behind independently — -d, --deprecated shipped at some point and was never added to Pages/Index.razor. Fixed in passing.

Tests

160 pass, 23 of them new, covering the three mapping behaviours, target-type spellings (long / Int64 / System.Int64), case-insensitive scalar names, overrides not leaking between runs, config resolution precedence, and unknown-setting rejection.

Verified end to end against the nullable test server: a bare Linq2GraphQL in a directory with the file generated the right namespace and client, applied "MacAddress": "string", and left only Longitude.cs in Scalars; an explicit --config in the same directory correctly did not inherit the discovered file's mappings.