Can't replace a package with Composer - composer-php

Question

I made an improvement (PR not merged yet) to an upstream library, guzzlehttp/psr-7, that's a dependency of another package that I depend on, spatie/crawler.
To force Composer to use my package instead of the upstream package, I tried the following:
I branched my fork of the library (branch name: cache-to-string) and updated its composer.json:
"name": "benmorel/guzzle-psr7",
"replace": {
"guzzlehttp/psr7": "1.6.*"
}
I updated my project's composer.json to use my fork instead:
"repositories": [
{
"type": "vcs",
"url": "https://github.com/BenMorel/psr7"
}
],
"require": {
"benmorel/guzzle-psr7": "dev-cache-to-string"
}
And ran composer update, which fails with the following error:
Your requirements could not be resolved to an installable set of packages.
Problem 1
The requested package benmorel/guzzle-psr7 could not be found in any version, there may be a typo in the package name.
How to fix this?

Answer 1

You don't need to change package name in your fork. You don't need to change composer.json of your fork at all. All you need is to add your fork to repositories section and change constraint of required package to use your dev branch:
"repositories": [
{
"type": "vcs",
"url": "https://github.com/BenMorel/psr7"
}
],
"require": {
"guzzlehttp/psr7": "dev-cache-to-string as 1.6.1"
}
Composer will override original guzzlehttp/psr7 package by version from your repository.
Using alias for branch may be required if some other package require guzzlehttp/psr7 - dev-cache-to-string will not match ^1.4. If you use dev-cache-to-string as 1.6.1 as a constraint, your branch will be detected as 1.6.1 release.