use lazyregexp for various regular expressions

[thaJeztah]

• alternative to use sync.OnceValue for various regular expressions #15

Using regex.MustCompile consumes a significant amount of memory when importing the package, even if those regular expressions are not used.

This changes compiling the regular expressions to use a lazyregexp package so that they're only compiled the first time they're used.

There are various regular expressions remaining that are still compiled on import, but these are exported, so changing them to a sync.OnceValue would be a breaking change; we can still decide to do so, but leaving that for a follow-up.

To verify, compile a basic binary importing the package;

package main

import _ "github.com/distribution/reference"

func main() {}

Before:

for i in $(seq 1 5); do GODEBUG=inittrace=1 ./before 2>&1 | grep distribution/reference; done

init github.com/distribution/reference @0.94 ms, 0.22 ms clock, 415712 bytes, 3599 allocs
init github.com/distribution/reference @0.39 ms, 0.22 ms clock, 415712 bytes, 3599 allocs
init github.com/distribution/reference @0.39 ms, 0.23 ms clock, 415712 bytes, 3599 allocs
init github.com/distribution/reference @0.45 ms, 0.27 ms clock, 415712 bytes, 3599 allocs
init github.com/distribution/reference @0.38 ms, 0.24 ms clock, 415712 bytes, 3599 allocs

After:

for i in $(seq 1 5); do GODEBUG=inittrace=1 ./after 2>&1 | grep distribution/reference; done

init github.com/distribution/reference/internal/lazyregexp @0.85 ms, 0 ms clock, 0 bytes, 0 allocs
init github.com/distribution/reference @1.0 ms, 0.16 ms clock, 238680 bytes, 1383 allocs
init github.com/distribution/reference/internal/lazyregexp @0.33 ms, 0 ms clock, 0 bytes, 0 allocs
init github.com/distribution/reference @0.42 ms, 0.16 ms clock, 238680 bytes, 1383 allocs
init github.com/distribution/reference/internal/lazyregexp @0.39 ms, 0 ms clock, 0 bytes, 0 allocs
init github.com/distribution/reference @0.47 ms, 0.19 ms clock, 238680 bytes, 1383 allocs
init github.com/distribution/reference/internal/lazyregexp @0.36 ms, 0 ms clock, 0 bytes, 0 allocs
init github.com/distribution/reference @0.47 ms, 0.14 ms clock, 238680 bytes, 1383 allocs
init github.com/distribution/reference/internal/lazyregexp @0.29 ms, 0 ms clock, 0 bytes, 0 allocs
init github.com/distribution/reference @0.38 ms, 0.15 ms clock, 238680 bytes, 1383 allocs

[codecov]

Codecov Report

❌ Patch coverage is 65.00000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.02%. Comparing base (6ccba5a) to head (34ca3d7).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/lazyregexp/lazyregexp.go	65.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
- Coverage   84.21%   83.02%   -1.19%     
==========================================
  Files           5        6       +1     
  Lines         304      324      +20     
==========================================
+ Hits          256      269      +13     
- Misses         38       45       +7     
  Partials       10       10              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.