Add "from-empty-schema" option for "diff" command

[guilliamxavier]

Q	A
Type	feature
BC Break	no
Fixed issues	#820

Summary

Allow to execute migrations:diff --from-empty-schema
(as alternative to migrations:dump-schema but using the mapping instead of the database)

[guilliamxavier]

Not tested yet (hence draft) but WDYT?

[guilliamxavier]

Update: I have tested the patch locally and I confirm it works as expected 😃 (but writing an automated test would be another story...)

[goetas]

I like this change!

A test should test the createEmptySchema method asserting something on the expected output.
(the current changes to the tests are just making sure that args are read as expected)

[guilliamxavier]

@goetas: Thanks, I have added tests (but I'm not sure because I couldn't mock the new Schema(...) in DiffGenerator::createEmptySchema()...)

[guilliamxavier]

I don't know why the "continuous-integration/travis-ci" check is blocked at "Expected — Waiting for status to be reported"... you can see that it passed: https://travis-ci.org/github/doctrine/migrations/builds/700372177

Anyway, this is now ready for review @goetas 🙂

[greg0ire]

Please kindly squash your commits together. If you don't, we'll try to remember to do it for you but it's best if you save us this trouble.

How to do that?

1. git rebase -i origin/2.3.x, assuming origin is a git remote that points to this repository, and not your fork. If you're not sure what your remotes are, run git remote -vvv, there should be your fork and the holy/reference/base/origin/whatever-you-call-it repository.
2. A window will show up with many lines, replace pick with fixup on every line but the first one
3. Close your editor, git should do its magic, and you should end up with one commit
4. Use git push --force to overwrite what you already push. Don't forget the --force option otherwise git will try to merge both things together.

[greg0ire]

Can you please add some documentation?

[guilliamxavier]

@greg0ire: done and done ;)

[goetas]

thanks @guilliamxavier

I think that I will have fun times when merging back this to master :)

[alzee]

Thanks @guilliamxavier
Great job!