🐛 `ffigen`: Struct member function pointer does **not** rename reserved keyword parameters (top-level functions correctly do)

[dzylikecode]

Version
ffigen: 20.0.0
Dart: 3.10.0
Platform: Linux

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Summary

When generating bindings, top-level C functions have their parameter names sanitized correctly (e.g., in → in$), but struct field function pointers do not.

This inconsistency results in invalid Dart code when the C parameter name is a Dart reserved keyword.

This issue is related to #512, but this time the bug is specifically inside struct member function pointers rather than top-level functions.

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🔄 Minimal reproducible example

C header (test.h)

void var(void *in);

struct cls {
    void (*var)(void *in);
};

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📄 Generated Dart code

✅ Top-level function (correct)

@ffi.Native<ffi.Void Function(ffi.Pointer<ffi.Void>)>(symbol: 'var')
external void var$(ffi.Pointer<ffi.Void> in$);

Notice in was correctly renamed to in$.

---

❌ Struct field function pointer (incorrect)

final class cls extends ffi.Struct {
  external ffi.Pointer<
      ffi.NativeFunction<
          ffi.Void Function(ffi.Pointer<ffi.Void> in)>> var$1;
}

This still contains:

... Function(ffi.Pointer<ffi.Void> in)

where in is a Dart reserved keyword → Dart compilation fails.

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❗ Problem

ffigen already has logic to rename reserved keywords for parameters in top-level functions, but this renaming is not applied to:

• function pointer parameters inside struct fields
• function pointer typedefs
• callbacks

This inconsistency causes generated code to be syntactically invalid.

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✅ Expected behavior

ffigen should apply the same identifier sanitization logic everywhere, including:

• top-level functions
• nested typedefs
• struct field function pointers
• callback signatures

Example of expected output:

ffi.Void Function(ffi.Pointer<ffi.Void> in$)

or:

ffi.Void Function(ffi.Pointer<ffi.Void> arg0)