63 lines
2.9 KiB
Markdown
63 lines
2.9 KiB
Markdown
<!--
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tagline: On gracefully resolving conflicts while merging
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-->
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# Resolving merge conflicts
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When working as a team on the same Composer project, you will eventually run into a scenario
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where multiple people added, updated or removed something in the `composer.json` and
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`composer.lock` files in multiple branches. When those branches are eventually merged
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together, you will get merge conflicts. Resolving these merge conflicts is not as straight
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forward as on other files, especially not regarding the `composer.lock` file.
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> **Note:** It might not immediately be obvious why text based merging is not possible for
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> lock files, so let's imagine the following example where we want to merge two branches;
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>
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> - Branch 1 has added package A which requires package B. Package B is locked at version `1.0.0`.
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> - Branch 2 has added package C which conflicts with all versions below `1.2.0` of package B.
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>
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> A text based merge would result in package A version `1.0.0`, package B version `1.0.0`
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> and package C version `1.0.0`. This is an invalid result, as the conflict of package C
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> was not considered and would require an upgrade of package B.
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## 1. Reapplying changes
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The safest method to merge Composer files is to accept the version from one branch and apply
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the changes from the other branch.
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An example where we have two branches:
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1. Package 'A' has been added
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2. Package 'B' has been removed and package 'C' is added.
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To resolve the conflict when we merge these two branches:
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- We choose the branch that has the most changes, and accept the `composer.json` and `composer.lock`
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files from that branch. In this case, we choose the Composer files from branch 2.
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- We reapply the changes from the other branch (branch 1). In this case we have to run
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`composer require package/A` again.
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## 2. Validating your merged files
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Before committing, make sure the resulting `composer.json` and `composer.lock` files are valid.
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To do this, run the following commands:
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```sh
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php composer.phar validate
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php composer.phar install [--dry-run]
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```
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## Important considerations
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Keep in mind that whenever merge conflicts occur on the lock file, the information, about the exact version
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new packages were locked on for one of the branches, is lost. When package A in branch 1 is constrained
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as `^1.2.0` and locked as `1.2.0`, it might get updated when branch 2 is used as baseline and a new
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`composer require package/A:^1.2.0` is executed, as that will use the most recent version that the
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constraint allows when possible. There might be a version 1.3.0 for that package available by now, which
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will now be used instead.
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Choosing the correct [version constraints](../articles/versions.md) and making sure the packages adhere
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to [semantic versioning](https://semver.org/) when using
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[next significant release operators](versions.md#next-significant-release-operators) should make sure
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that merging branches does not break anything by accidentally updating a dependency.
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