Implement ApplyPatchToIndex Class

[dometto]

This started as an experiment to see how difficult it would be to implement a version of JGit's ApplyCommand that applies a patch to a tree in the repository, rather than to the working directory. See here for a description of the functionality that is currently missing.

The new Plumbing::ApplyPatchToIndex class is a ruby implementation of this JGit class, or at least of its main logic:

• The ApplyPatchToIndex#build_map method executes the JGit ApplyCommand.calllogic
• The ApplyPatchToIndex#apply method executes the JGit ApplyCommand.apply logic

In writing these methods I just followed the Java code step by step and attempted to translate it to some sane Ruby. It turned out the actual patch application logic was relatively simple: much of the code in the JGit class concerns initializing, copying, and looping over arrays, which we can vastly simplify thanks to JRuby. And another large part of the JGit class concerns making the changes on the file system, which we're not interested in.

I was amazed to find out that the code seems to actually work. :) Try running this test script:

require './lib/rjgit.rb'
include RJGit

r = Repo.new('/path/to/repo')

patch = ''
diff  = RJGit::Porcelain.diff(r, {:patch => true, :new_rev => r.commits[1].id, :old_rev => r.commits[0].id})
diff.each {|x| patch << x[:patch]}

builder = Plumbing::ApplyPatchToIndex.new(r, patch)

builder.build_map

puts builder.treemap.inspect

This will produce a treemap corresponding to a revert of the last commit of your target repo. You could theoretically then commit this to the repository by calling builder.commit. Neat, if I do say so myself. :)

This at least gives us some basis for judging whether we want to implement this code in RJGit, or whether it is too hackish and we need to submit a patch to JGit. @bartkamphorst: I would understand if you still prefer the second option, but wanted to give this a go at least.

Note: the only logic that I haven't implemented yet, because I don't understand it well enough, is this bit concerning newlines.

[coveralls]

Coverage decreased (-0.09%) to 99.25% when pulling bf7e22f on dometto:apply_tree into 919e739 on repotag:master.

[dometto]

@bartkamphorst if you think we should implement this functionality ourselves for now, I'll work on adding tests for this.

[dometto]

Added specs. If travis passes, should be ready to merge!

[bartkamphorst]

Test suite on Travis succeeded, but coveralls complains: `Coveralls encountered an exception:

NoMethodError
undefined method coverage' for #<SimpleCov::SourceFile:0x56dae6>. Any ideas?

[dometto]

Where are you seeing this coveralls exception?

[bartkamphorst]

Where are you seeing this coveralls exception?

In Travis (e.g., #329.1):

[bartkamphorst]

See my 'Single comments'. 🤔

[dometto]

Test suite on Travis succeeded, but coveralls complains: `Coveralls encountered an exception:

Fixed by updating coveralls in the Gemfile

[bartkamphorst]

🎆