Access configuration flag in custom-esbuild plugin

[RaulPROP]

Is your feature request related to a problem? Please describe.
This is a feature request.

Describe the solution you'd like
I'd love to be able to access the configuration string (like in custom-webpack with the targetOptions.configuration) in the esbuild plugins and indexHtmlTransformer (i.e.: the --configuration flag).

Describe alternatives you've considered
The only alternative that I see is overriding the plugins and indexHtmlTransformer for each configuration (i.e.: having a plugin-development.ts, plugin-production.ts, etc).

Additional context
I guess this is related to #1661 in some way.

[just-jeb]

The --configuration flag is already accessible in esbuild plugins via the factory function pattern.

When a plugin file exports a factory function (instead of a plugin directly), the builder calls it with (builderOptions, target) where target is { project, target, configuration }.

Example:

import type { Plugin } from 'esbuild';
import type { Target } from '@angular-devkit/architect';
import type { ApplicationBuilderOptions } from '@angular/build';

export default (builderOptions: ApplicationBuilderOptions, target: Target): Plugin => ({
  name: 'my-plugin',
  setup(build) {
    const configuration = target.configuration ?? 'default';
    build.initialOptions.define = {
      ...build.initialOptions.define,
      'process.env.CONFIGURATION': JSON.stringify(configuration),
    };
  },
});

This is documented in the README under the factory function section. Closing as the feature already exists.

[just-jeb]

The feature is already implemented — target.configuration has always been passed to factory plugins and indexHtmlTransformer functions. What was missing was documentation showing this clearly.

PR #2192 adds:

• Updated README examples for factory plugins and indexHtmlTransformer showing target.configuration (and target.project) with inline comments
• A runtime integration test that builds with a plugin + transformer both reading target.configuration and verifies the value ends up in the JS bundle and index.html — so this is now regression-tested

Example (plugin factory):

export default (builderOptions: ApplicationBuilderOptions, target: Target): Plugin => ({
  name: 'my-plugin',
  setup(build) {
    // target.configuration = active --configuration flag (e.g. "production", "staging")
    build.initialOptions.define.activeConfig = JSON.stringify(target.configuration ?? 'default');
  },
});

Example (indexHtmlTransformer):

module.exports = (indexHtml, target) => {
  // target.configuration is the active build configuration
  return indexHtml.replace("</head>", `<meta name="config" content="${target.configuration}">
</head>`);
};