为什么composer被设计为使用两个文件：composer.json和composer.lock，而不是一个

Question

I want to create my own package manager, and currently reviewing existing solutions.

I'm playing with PHP's Composer now, and it was quite surprising that it has two files:

• composer.json for project configuration, and non-pinned dependencies

• composer.lock for exact pinned dependencies

I do understand why one needs to pin dependencies, .lock information by itself seems logical to me.

What I do not understand is why project metadata was split into two files.

Can anyone explain, why it was designed this way? Why deps could not be pinned right in the composer.json?

UPD. Turns out, Rust's Cargo has the same two file configuration in place, and has a nice explanation of the meaning of the .lock file: http://doc.crates.io/guide.html#cargotoml-vs-cargolock

Answer 1

.lock information is absolutely pinned, typically created by a composer update request based on the json information... but developers don't necessarily want to pin everything to an exact version, and without that .json file they have to upgrade the .lock file manually for every version upgrade of their dependencies.

The .lock also holds dependencies of dependencies, and dependencies of dependencies of dependencies, etc... whereas the .json file only holds immediate dependencies.... and as a developer, you should only need to control your immediate dependencies, and allow those libraries to control their own dependencies via their own .json files

Basically, you should build your application against the json but deploy against the .lock