[WIP] cl: ast.OverloadFuncDecl preload overload func

[visualfc]

deps by https://github.com/goplus/gogen/pull/541

• ast.OverloadFuncDecl preload overload func
• remove pkgCtx.overpos

[gemini-code-assist[bot]]

Summary of Changes

Hello @visualfc, I'm Gemini Code Assist[^1]! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces fundamental changes to the compiler's preloading mechanism to properly support ast.OverloadFuncDecl. It modifies how functions and methods are registered and represented internally, enabling the compiler to recognize and manage overloaded entities. By creating specialized internal objects and a synthetic dispatcher for overloads, this change lays the groundwork for robust overload resolution within the compilation process.

Highlights

• Enhanced Function Preloading: The preloadFuncDecl internal function now accepts an overload boolean parameter, allowing the compiler to differentiate between standard and overloaded function declarations during the initial preloading phase.
• Specialized Overload Handling: New conditional logic has been introduced to create distinct internal representations for overloaded functions and methods. Instead of directly calling loadFunc, overloaded entities now trigger the creation of gogen.NewOverloadFunc or gogen.NewOverloadMethod objects.
• Synthetic Overload Dispatcher: When an ast.OverloadFuncDecl is encountered, the system now generates a synthetic ast.FuncDecl that acts as an overload dispatcher. This dispatcher function is marked as overloaded and accepts a single any type parameter, facilitating runtime overload resolution.
• New Constant for Overload Arguments: A new constant, __xgo_overload_args__, has been added to serve as the parameter name for the synthetic overload dispatcher function, ensuring consistent naming.

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[niupilot[bot]]

Code Review Summary

Clean implementation of overload function preloading. Three areas need attention:

Critical:

• Line 1071: Unsafe type lookup/assertion - add nil checks to prevent panic

Documentation:

• Line 1361: Add doc comment for overloadArgs constant
• Line 1312-1319: Explain placeholder signature purpose

Style:

• Line 1312-1319: Remove unnecessary & in Field literal

No performance or security vulnerabilities found beyond the nil check issue.