fix: circular dependencies

[tpraxl]

This commit addresses circular dependencies between index.js and promise.js, as well as within files in the lib directory such as pool.js and pool_connection.js.

It introduces a new common.js module to centralize shared functionalities, thus breaking the direct dependencies among these files.

This approach resolves issues with the @opentelemetry/instrumentation-mysql2 package, which was losing several exports due to the circular dependencies.

You can reproduce the problem with this simple test repo:

https://github.com/tpraxl/test-esm-mysql-otel

Follow the instructions in the README.md to see the respective warnings.

To verify that this PR fixes the issue, check it out, run npm i && npm pack and install the fixed version into the test repo using npm i $PATH_TO_MYSQL2/mysql2-3.11.3.tgz. Run npm start again in the checked out test repo to see the warnings vanish.

This PR would fix open-telemetry/opentelemetry-js-contrib#1511

[codecov]

Codecov Report

Attention: Patch coverage is 97.18310% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.16%. Comparing base (d94bfaa) to head (fbb8ab1).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
promise.js	92.85%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3081      +/-   ##
==========================================
+ Coverage   88.13%   88.16%   +0.02%     
==========================================
  Files          71       74       +3     
  Lines       12890    12919      +29     
  Branches     1355     1358       +3     
==========================================
+ Hits        11361    11390      +29     
  Misses       1529     1529              

Flag	Coverage Δ
compression-0	88.16% <97.18%> (+0.02%)	⬆️
compression-1	88.16% <97.18%> (+0.02%)	⬆️
tls-0	87.58% <97.18%> (+0.02%)	⬆️
tls-1	87.92% <97.18%> (+0.02%)	⬆️

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[wellwelwel]

Thanks, @tpraxl 🚀

I remember experiencing an error with rollup because of this.

Just a small recommendation, moving from ./common.js to ./lib/common.js 🙋🏻‍♂️

[tpraxl]

@wellwelwel You have a point there. In that case however, it feels weird to arbitrarily stuff some exported functions together in lib/common.js .

It made sense when we were talking about commons for index.js and promise.js, but in lib, I would split common.js up into the following files and get rid of common.js

• lib/create_connection.js
• lib/create_pool.js
• lib/create_pool_cluster.js

I'm working on it and will push the result

[wellwelwel]

Hey @tpraxl, I tested your changes with rollup:

---

• index.js

import mysql from 'mysql2/promise';

mysql.createPool({});

• rollup.config.js

import { defineConfig } from 'rollup';
import { nodeResolve } from '@rollup/plugin-node-resolve';
import commonjs from '@rollup/plugin-commonjs';
import json from '@rollup/plugin-json';

export default defineConfig({
  input: 'index.js',
  output: {
    file: 'dist.js',
  },
  plugins: [nodeResolve(), commonjs(), json()],
});

• package.json

{
  "type": "module",
  "devDependencies": {
    "@rollup/plugin-commonjs": "^28.0.0",
    "@rollup/plugin-json": "^6.1.0",
    "@rollup/plugin-node-resolve": "^15.3.0",
    "rollup": "^4.24.0"
  },
  "dependencies": {
    "mysql2": "file:../node-mysql2"
  }
}

---

I'll try to investigate this further.

[tpraxl]

Thanks for your finding. No need to investigate further IMHO, I would propose to extract PromiseConnection, PromisePool and PromisePoolConnection into lib. Each in its own file and to resolve the circular dependency that way.

See https://github.com/tpraxl/node-mysql2/pull/1/files

If these changes are OK for you, I'll merge them into fix/circular-dependencies and update this PR.

[tpraxl]

@wellwelwel are you fine with my changes?
See https://github.com/tpraxl/node-mysql2/pull/1/files
I would merge them into this PR if you are ok with it.