Look for COMPOSER_RUNTIME_BIN_DIR, not COMPOSER_BIN_DIR

[stevegrunwell]

Since Composer 2.2.6 (the latest version), Composer exposes the COMPOSER_RUNTIME_BIN_DIR environment variable when running as a vendor script.

However, there are a few conditions under which this variable may not be available:

• When running binaries defined by the root package
• When running on Composer < 2.2.6
• When executing the script outside of a Composer script context

This PR replaces the check for COMPOSER_BIN_DIR with COMPOSER_RUNTIME_BIN_DIR and adds a fallback that uses composer config --absolute bin-dir; if we're able to determine a project's Composer bin-dir, we'll strip this off the front of a user's $PATH.

(Re-)fixes #2.

[stevegrunwell]

Pulled and verified this branch into a local project that uses the following Composer script:

"test": [
    "vendor/bin/shellcheck --debug bin/*"
]

Output

Composer 2.2.5

$ composer --version
Composer version 2.2.5 2022-01-21 17:25:52
$ composer test
> vendor/bin/shellcheck --debug bin/*
[DEBUG] COMPOSER_RUNTIME_BIN_DIR not found, checking Composer configuration
[DEBUG] Stripping '/Users/steve/Code/my-project/vendor/bin' from $PATH
[DEBUG] Using /usr/local/bin/shellcheck
[DEBUG] Running `shellcheck bin/my-script`

Composer 2.2.6

Note: The COMPOSER_RUNTIME_BIN_DIR gets written to the vendor/bin/shellcheck file, so I had to wipe out that file after upgrading Composer in order to have it included.

$ composer --version
Composer version 2.2.6 2022-02-04 17:00:38
$ composer test
> vendor/bin/shellcheck --debug bin/*
[DEBUG] Stripping '/Users/steve/Code/my-project/vendor/bin' from $PATH
[DEBUG] Using /usr/local/bin/shellcheck
[DEBUG] Running `shellcheck bin/my-script`