No Context Propagation in Convert() Function

[richardwooding]

Summary

The main Convert() function doesn't accept a context.Context parameter, preventing cancellation, timeouts, and observability integration.

Location

cel2sql.go:20

Issue

func Convert(ast *cel.Ast, opts ...ConvertOption) (string, error)

This prevents:

• Cancellation of long-running conversions
• Timeout protection for complex expressions
• Distributed tracing integration
• Resource cleanup on context cancellation

Inconsistent with pg.TypeProvider.LoadTableSchema() which does use context.

Impact

High - Large or complex CEL expressions could run indefinitely with no way to cancel. Cannot integrate with timeout/cancellation patterns common in web services.

Updated Solution (Using Functional Options)

With the new functional options API (from #62), we can add context support as a non-breaking change using WithContext() option!

Implementation Plan

1. Add Context Option

type convertOptions struct {
    schemas map[string]pg.Schema
    ctx     context.Context  // NEW
}

func WithContext(ctx context.Context) ConvertOption {
    return func(o *convertOptions) {
        o.ctx = ctx
    }
}

2. Update Converter

type converter struct {
    str     strings.Builder
    typeMap map[int64]*exprpb.Type
    schemas map[string]pg.Schema
    ctx     context.Context  // NEW
}

3. Add Context Checks

Add helper method and checks at key recursion points:

• visit() - main traversal entry
• visitCall() - every function call
• visitComprehension() - before processing comprehensions
• Individual comprehension handlers

func (con *converter) checkContext() error {
    if con.ctx == nil {
        return nil
    }
    return con.ctx.Err()
}

func (con *converter) visit(expr *exprpb.Expr) error {
    if err := con.checkContext(); err != nil {
        return fmt.Errorf("conversion cancelled: %w", err)
    }
    // ... rest of function
}

Usage

Backward compatible - existing code works without changes:

sql, err := cel2sql.Convert(ast)

With context - opt-in cancellation support:

ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()

sql, err := cel2sql.Convert(ast, 
    cel2sql.WithContext(ctx),
    cel2sql.WithSchemas(schemas))

Benefits

• ✅ Non-breaking change (unlike original proposal)
• ✅ Opt-in (only pay cost if context provided)
• ✅ Consistent with WithSchemas() pattern
• ✅ No need for separate ConvertWithContext() function
• ✅ No need for v3 major version bump

Files to Change

1. cel2sql.go - Add option, update converter, add checks
2. context_test.go - NEW: Tests for cancellation/timeout
3. examples/context/ - NEW: Example demonstrating usage

Original Proposal (Superseded)

Add ConvertWithContext() and deprecate Convert(), or increment to v3

The functional options API provides a much cleaner solution!