test: Add comprehensive benchmarks and go.mod for easier testing

[pedro-stanaka]

Summary

This PR adds comprehensive benchmarks to measure sourcemap parsing performance across various file sizes and scenarios.

What's Added

1. Go Module Support (go.mod)

• Added go.mod file to enable module-aware builds
• Makes it significantly easier to run tests and benchmarks
• No more GOPATH configuration required
• Maintains compatibility with Go 1.18+

2. Synthetic Benchmarks (bench_synthetic_test.go)

• Tests parsing performance on generated sourcemaps from 5KB to 10MB
• Provides consistent, reproducible performance measurements
• Includes memory allocation analysis

3. Real-World Benchmarks (bench_large_test.go)

• Downloads and caches real sourcemaps from popular libraries
• Tests with jQuery (~135KB), Angular (~2.7MB), and other frameworks
• Includes gzipped parsing benchmarks (common in production)

4. Enhanced Makefile

New targets for performance analysis:

make bench          # Run all benchmarks
make bench-mem      # Profile memory usage
make bench-cpu      # Profile CPU usage
make bench-compare  # Compare before/after performance

Sample Output

BenchmarkSyntheticSizes/Tiny-11         10     66 MB/s      4824 B/op       34 allocs/op
BenchmarkSyntheticSizes/Small-11        10     93 MB/s     17720 B/op       44 allocs/op
BenchmarkSyntheticSizes/Medium-11       10    104 MB/s     65112 B/op       56 allocs/op
BenchmarkSyntheticSizes/Large-11        10    113 MB/s    324696 B/op      140 allocs/op
BenchmarkSyntheticSizes/XLarge-11       10    125 MB/s   1533336 B/op      242 allocs/op
BenchmarkSyntheticSizes/XXLarge-11      10    118 MB/s   6056483 B/op      444 allocs/op

Rationale for go.mod

While testing these benchmarks, I found it quite difficult to run tests without Go module support:

• Required manual GOPATH configuration
• Import path resolution issues
• Inconsistent behavior across different Go versions and environments

Adding a minimal go.mod file solves these issues while maintaining backward compatibility for users who prefer GOPATH mode.

Why Benchmarks Matter

Having comprehensive benchmarks allows:

• Performance regression detection - Catch slowdowns before they reach production
• Optimization validation - Measure the impact of performance improvements
• Memory usage tracking - Monitor allocation patterns and memory efficiency
• Cross-version comparison - Compare performance across Go versions

Testing

The benchmarks work with the existing test infrastructure:

# Run specific benchmark
go test -bench=BenchmarkSyntheticSizes/Large -benchmem

# Run all benchmarks
go test -bench=. -benchmem

# Compare performance with benchstat
make bench-compare
# ... make changes ...
make bench-new

Notes

• Benchmarks cache downloaded sourcemaps in /tmp to avoid repeated downloads
• All benchmarks are in *_test.go files and don't affect the library size
• Compatible with existing CI/CD pipelines (standard go test)
• No new dependencies required

This provides a foundation for tracking and improving parsing performance over time.

[vmihailenco]

Adding a minimal go.mod file solves these issues while maintaining backward compatibility for users who prefer GOPATH mode.

AFAIR the problem is that we already have v2.x version and adding go.mod will require updating imports to sourcemap/v2. Am I wrong?

We could remove all the v2.x tags, but that's probably even worse...