[WIP] Update Go AST parser with latest Antlr grammar and test coverage

[Copilot]

• Explore the repository structure and understand the changes
• Verify all Go tests pass (41 tests: 40 pass, 1 skip)
• Confirm GoGenericsTest.kt exists with 7 tests for Go 1.18+ features
• Confirm GoNumberLiteralsTest.kt exists with 7 tests for number literals
• Verify grammar files (GoLexer.g4, GoParser.g4) are updated with new flat structure
• Verify GoParserBase.java has new helper methods (isOperand, isConversion, isMethodExpr)
• Verify GoFullIdentListener.kt refactoring is complete with new methods
• Verify all test coverage: generics, type constraints, number literals, underscore separators
• Run code review tool for quality check
• Run security checks with CodeQL
• Finalize and complete the task

Original prompt

feat: modernize Go AST parser with latest Antlr grammar and add Go 1.18+ test coverage

Summary

Updated the Go AST parser to use the latest Antlr grammar and added comprehensive test coverage for modern Go syntax including generics and new number literals.

Changes Made

Core Grammar Updates

• Updated Antlr Go grammar files (GoLexer.g4, GoParser.g4) to latest version with significant structural changes
• Enhanced GoParserBase.java with new helper methods for parsing disambiguation (isOperand(), isConversion(), isMethodExpr())

Major Listener Refactoring

• Completely rewrote GoFullIdentListener.kt to handle new flat primaryExpr grammar structure:
  • handlePrimaryExprCall(): Fixed to handle new non-left-recursive structure and support chained method calls
  • handleForPrimary(): Improved local variable resolution with proper isForLocalVar flag handling
  • getValueFromPrintf(): Fixed to find ArgumentsContext at any position in new grammar
  • Added robust support for receiver type resolution and method chaining

Test Coverage Improvements

• Fixed all test failures: All 41 tests now pass (40 pass, 1 skip)
• Added GoGenericsTest.kt with 7 comprehensive tests for Go 1.18+ generics:
  • Generic function declarations and calls
  • Generic type definitions with multiple type parameters
  • Methods on generic types
  • Type constraints and interface with type unions
  • Underlying type constraints with tilde (~type)
• Added GoNumberLiteralsTest.kt with 7 tests for new number literal syntax:
  • Binary literals (0b1010, 0B1111_0000)
  • Underscore separators in all number types (1_000_000)
  • Hexadecimal float literals (0x1.Fp+0)
  • Modern imaginary literals with all number types

Technical Details

The main challenge was adapting to the new Antlr grammar where primaryExpr changed from:

// Old left-recursive structure
primaryExpr: operand | primaryExpr selector | ...

// New flat structure  
primaryExpr: (operand | conversion | methodExpr) (DOT IDENTIFIER | index | slice_ | typeAssertion | arguments)*

This required completely rewriting the method call parsing logic to iterate through flat children instead of recursive descent.

Testing

• All existing tests continue to pass
• Added 14 new tests covering Go 1.18+ features
• Comprehensive coverage of edge cases and chained method calls
• Tests validate both parsing success and correct AST extraction

Resolves build failures after Antlr grammar update and provides future-ready support for modern Go syntax.

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🤖 Augment PR Summary

Summary: Modernizes chapi-ast-go by updating the ANTLR Go grammar and adapting the Go AST listener to the new flat primaryExpr structure.
Changes: Adds/updates parser disambiguation helpers and expands test coverage for Go 1.18+ generics and modern numeric literal formats.

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