Strategy to override a class in a library installed with Composer

In composer.json, under ["autoload"]["psr-4"], add an entry with namespace as the key and path as the value:

{     "autoload": {         "psr-4": {             "BuggyVendor\\Namespace\\": "myfixes/BuggyVendor/Namespace"         }     }}

Copy files you want to override under that path (keeping sub-namespace directory structure) and edit them there. They will be picked in preference to the library package's original "classpath". It would seem that namespace->path mappings added to composer.json in this manner are considered before those added by required packages. Note: I just tried it and it worked, though I don't know if it is an intended feature or what possible gotchas are.

EDIT: found a gotcha. Sometimes when you subsequently require another package with composer require vendor/package, you will "lose" the override. If this happens, you must issue composer dump-autoload manually. This will restore the correct autoload order honoring your override.

There is one more option.In case you need to rewrite the only class you can use files in composer.json like this

 "autoload": {     "files": ["path/to/rewritten/Class.php"]  }

So if you want to rewrite class Some\Namespace\MyClass put it like this

#path/to/rewritten/Class.phpnamespace Some\Namespace;class MyClass {  #do whatever you want here}

Upon each request composer will load that file into memory, so when it comes to use Some\Namespace\MyClass - implementation from path/to/rewritten/Class.php will be used.

Adding these last 2 lines to the autoload section of my composer.json is what worked for me when I wanted to override just one file within the vendors directory:

"autoload": {            "classmap": [        "database"    ],    "psr-4": {        "App\\": "app/"    },    "exclude-from-classmap": ["vendor/somepackagehere/blah/Something.php"],    "files": ["app/Overrides/Something.php"]},

Remember that the namespace within app/Overrides/Something.php needs to match whatever the original was in vendor/somepackagehere/blah/Something.php.

Remember to run composer dump-autoload after editing the composer.json.

_{Docs: https://getcomposer.org/doc/04-schema.md#files}