Preserve relative paths for editable dependencies in output

[macro1]

Accomplishes preservation of relative dependency paths by reverting back to input requirements definition for editable dependencies.

There are a couple prior attempts of this. The two I read through treated this like a formatting problem, I'm not sure it is. The issue, as has been pointed out in #204 is that paths are converted into urls in the form of absolute paths within pip.

If we maintain knowledge of the original relative paths within pip-tools, the values will be maintained more faithfully, and the complexity should be lower.

This PR accomplishes it by forcing the return value from parse_requirements() to give the values we need elsewhere. A better approach may be to return something different than InstallRequirement or preserve the relationship with the parsed requirement and provide both where it makes sense.

Contributor checklist

• [x] Included tests for the changes.
• [x] PR title is short, clear, and ready to be included in the user-facing changelog.

Maintainer checklist

• [x] Verified one of these labels is present: backwards incompatible, feature, enhancement, deprecation, bug, dependency, docs or skip-changelog as they determine changelog listing.
• [ ] Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[chrysle]

The change looks good to me (we'll need a unit test, though). The CI failure is unrelated, I'll look into it.

A better approach may be to return something different than InstallRequirement

Do you have anything in mind?

[macro1]

The change looks good to me (we'll need a unit test, though). The CI failure is unrelated, I'll look into it.

A better approach may be to return something different than InstallRequirement

Do you have anything in mind?

I was mainly thinking we could add a new structure containing the InstallRequirement and any other attributes pip-tools may need to track. However, I understand that it would impact many internal interfaces, which could pose some challenges.

[chrysle]

Ah yes, I love Windows, too. Will review soon.

[chrysle]

@macro1 Could you look into fixing the linting errors?