Code Review

This pull request refactors the CallExpr AST node by moving it from ast/ast.go to ast/ast_gop.go and extends it to support keyword arguments. This is achieved by adding a Kwargs field to CallExpr and introducing a new KwargExpr node type. The changes are well-structured and consistent with the existing codebase. My only suggestion is to update the documentation for CallExpr to reflect its new capability.

Critical Issues

ast/ast_gop.go:92-95 - Missing Position Field

Critical: KwargExpr missing separator position field. Following the KeyValueExpr pattern (ast/ast.go:269-273), should include:

type KwargExpr struct {
    Name  *Ident    // argument name
    Sep   token.Pos // position of "=" or ":"
    Value Expr      // argument value
}

This is essential for error reporting, formatting tools, and IDE features.

ast/ast_gop.go:74 - Nil Pointer Risk

Security: Nil pointer panic if Fun is nil. Add nil check:

func (x *CallExpr) Pos() token.Pos {
    if x.Fun != nil {
        return x.Fun.Pos()
    }
    return x.Lparen
}

ast/ast_gop.go:97 - Nil Pointer Risk

Security: Nil pointer panic if Name is nil. Add nil check:

func (x *KwargExpr) Pos() token.Pos {
    if x.Name != nil {
        return x.Name.Pos()
    }
    if x.Value != nil {
        return x.Value.Pos()
    }
    return token.NoPos
}

ast/ast_gop.go:101 - Nil Pointer Risk

Security: Nil pointer panic if Value is nil. Add nil check:

func (x *KwargExpr) End() token.Pos {
    if x.Value != nil {
        return x.Value.End()
    }
    if x.Name != nil {
        return x.Name.End()
    }
    return token.NoPos
}

ast/walk.go - Missing AST Walker Updates

Security: The Walk function doesn't traverse Kwargs field or handle KwargExpr nodes. This causes security analysis tools to miss code in keyword arguments. Need to:

1. Update CallExpr case to walk Kwargs:

case *CallExpr:
    Walk(v, n.Fun)
    walkList(v, n.Args)
    walkList(v, n.Kwargs)  // Add this

2. Add KwargExpr case:

case *KwargExpr:
    Walk(v, n.Name)
    Walk(v, n.Value)

Style Issues

ast/ast_gop.go:97,101,105 - Inconsistent Receiver Naming

Expression nodes use x as receiver, not p. Update KwargExpr methods to use x.

ast/ast_gop.go:62 - Documentation Update

Update CallExpr comment to mention keyword arguments:

// A CallExpr node represents an expression followed by an argument list.
// The argument list may include positional arguments (Args) and/or 
// keyword arguments (Kwargs).

ast/ast_gop.go:97,101 - Missing Method Documentation

Add documentation comments for Pos() and End() methods following the pattern used elsewhere in the file.

Documentation Gap

This adds a new language feature (keyword arguments) but there are no:

• Syntax examples in code comments
• Updates to language specification files
• Usage examples showing the kwarg syntax

Consider adding examples showing the actual syntax (e.g., func(arg: value) or func(arg=value)).