fix(strawberry-shake): generate compilable upload mappers for multiple Upload fields

[cliedeman]

Problem

StrawberryShake generated invalid C# whenever a type or operation involved more than one Upload-typed field. The generated client failed to compile, which two upstream issues report:

• Strawberry shake generating duplicate members when multiple File Inputs exist on the same type ChilliCream/graphql-platform#9559 (v15.1.14, minimal repro): Type 'CreateTaskMutation' already defines a member called 'MapFilesFromTypeFileUpload' and A local variable or function named 'u' is already defined in this scope.
• Strawberry Shake generates invalid C# for mutations with multiple uploads ChilliCream/graphql-platform#7852 (v14.3): error CS0128: A local variable or function named 'u' is already defined in this scope for an input type with two Upload fields.

These are one root-cause area, two distinct defects in OperationServiceGenerator's file-mapper emission:

1. Reused local u. The Upload scalar mapper hardcoded its pattern variable to u, so an input type with several Upload fields emitted multiple value is Upload u ? u : null statements in the same method scope → CS0128.
2. Duplicate MapFilesFromType<T> member. The recursive descent in AddMapFilesOfInputTypeMethod had no dedup guard. When one input type had multiple fields of the same nested upload input type (e.g. CreateTaskInput { uploadOne: FileUpload, uploadTwo: FileUpload }), the nested mapper method was generated twice → "already defines a member".

Fix

src/StrawberryShake/CodeGeneration/src/CodeGeneration.CSharp/Generators/OperationServiceGenerator.cs

• Thread the dedup HashSet<string> through AddMapFilesOfInputTypeMethod and move the processed.Add(type.Name) guard to the top of that method, so each MapFilesFromType<T> is emitted exactly once whether reached from a top-level argument or via recursion.
• Replace the hardcoded u pattern variable in the scalar Upload mapper with the already-unique checkedVariable (value<Field>_i), so every upload field gets a unique local.

The change is equivalent for all existing single-upload cases (variable rename only); the committed snapshots and integration *.Client.cs files are updated accordingly.

Tests

New dedicated test class UploadMultipleFilesGeneratorTests with two cases:

• Generate_Should_CompileUniqueLocals_When_InputTypeHasMultipleUploadFields — input with two Upload scalar fields (isolates Strawberry Shake generates invalid C# for mutations with multiple uploads ChilliCream/graphql-platform#7852's u collision).
• Generate_Should_EmitSingleMapper_When_InputTypeHasMultipleFieldsOfSameUploadInputType — mirrors the Strawberry shake generating duplicate members when multiple File Inputs exist on the same type ChilliCream/graphql-platform#9559 repro structure (CreateTaskInput with two FileUpload fields, each FileUpload with two Upload fields), reproducing both the duplicate member and the u collision.

GeneratorTestHelper.AssertResult Roslyn-compiles the generated output, so both defects surface as real compile errors.

Before (RED):

Type 'TestQuery' already defines a member called 'MapFilesFromTypeFileUpload' with the same parameter types
A local variable or function named 'u' is already defined in this scope

After (GREEN): full StrawberryShake.CodeGeneration.CSharp.Tests project passes — 191 passed, 1 skipped (pre-existing), 0 failed.

Fixes ChilliCream#9559
Fixes ChilliCream#7852

— Claude
🤖 Generated with Claude Code