# SDL3 Header Parser - Agent Documentation

## Project Overview

This is an SDL3 header parser that converts C header files into Zig interfaces, JSON objects, and C mocks. Built specifically for SDL3 headers (developed against SDL 3.2.10), it focuses on generating Zig APIs.

**Key Points:**
- Not a real C parser - best-effort text transformation specifically for SDL3 headers
- Does not do proper AST elaboration or tokenization
- Simple to modify but brittle
- Requires Zig 0.15.2 and git

## Architecture

The codebase consists of several modules:
- `parser.zig` - Main entry point and orchestration
- `patterns.zig` - SDL3 pattern matching and declaration scanning
- `codegen.zig` - Zig code generation
- `mock_codegen.zig` - C mock generation
- `json_serializer.zig` - JSON output generation
- `dependency_resolver.zig` - Type dependency resolution
- `header_cache.zig` - Header caching for cross-file type resolution
- `io.zig` - Error handling utilities
- `types.zig` - Type mapping and conversions
- `naming.zig` - Naming conventions

## Developing

### Build System Patterns

**Custom Build Steps:**
The project uses custom Zig build steps for operations that need to happen during the build process:

```zig
const MakeDirStep = struct {
    step: std.Build.Step,
    dir_path: []const u8,

    pub fn create(b: *std.Build, dir_path: []const u8) *std.Build.Step {
        const self = b.allocator.create(MakeDirStep) catch @panic("OOM");
        self.* = .{
            .step = std.Build.Step.init(.{
                .id = .custom,
                .name = b.fmt("mkdir {s}", .{dir_path}),
                .owner = b,
                .makeFn = make,
            }),
            .dir_path = dir_path,
        };
        return &self.step;
    }

    fn make(step: *std.Build.Step, options: std.Build.Step.MakeOptions) !void {
        _ = options;
        const self: *MakeDirStep = @fieldParentPtr("step", step);
        try std.fs.cwd().makePath(self.dir_path);
    }
};
```

This pattern allows cross-platform directory creation and other filesystem operations during build without relying on shell commands.

### Error Handling
**CRITICAL:** Whenever actual errors are encountered (parsing failures, invalid declarations, missing types, etc.), you MUST call `io.emitError` to report them properly. Do NOT use `std.debug.print` for actual errors.

```zig
// Good - proper error reporting
try io.emitError(allocator, "Failed to parse struct field: {s}", .{field_name});

// Bad - don't use for errors
std.debug.print("Error: Failed to parse...\n", .{});
```

### Validation Process
After generating Zig code:
1. Output written to `tmp/` directory
2. `zig ast-check` runs on the temporary file
3. If passes: `zig fmt` runs, then copied to final destination
4. If fails: debug output written to `debug/` with `_fmterror.zig` suffix

### Memory Management
- Two cleanup functions exist with identical logic:
  - `freeDecls()` - frees a slice of declarations
  - `freeDeclDeep()` - frees a single declaration
- Both free all nested allocations (names, types, doc comments, params/fields/values/flags)

### Main APIs (Priority)
Focus areas: gpu, video, gamepad, joystick, input, event

Anything beyond these is not actively maintained.