Add GitRepo.staged_submodule_removals helper

Add a helper which will allow the pre-commit hook to check which
submodules are staged for removal so it can deal with the strange
subodule removal behavior accordingly.

Author: sds

lib/overcommit/exceptions.rb

@@ -5,6 +5,9 @@ class ConfigurationError < StandardError; end
   # Raised when trying to read/write to/from the local repo git config fails.
   class GitConfigError < StandardError; end
 
+  # Raised when there was a problem reading submodule information for a repo.
+  class GitSubmoduleError < StandardError; end
+
   # Raised when a {HookContext} is unable to setup the environment before a run.
   class HookSetupFailed < StandardError; end
 

lib/overcommit/git_repo.rb

@@ -1,3 +1,5 @@
+require 'iniparse'
+
 module Overcommit
   # Provide a set of utilities for certain interactions with `git`.
   module GitRepo
@@ -189,5 +191,51 @@ def restore_cherry_pick_state
         @cherry_head = nil
       end
     end
+
+    # Contains information on a submodule.
+    Submodule = Struct.new(:path, :url)
+
+    # Returns the submodules that have been staged for removal.
+    #
+    # `git` has an unexpected behavior where removing a submodule without
+    # committing (i.e. such that the submodule directory is removed and the
+    # changes to the index are staged) and then doing a hard reset results in
+    # the index being wiped but the empty directory of the once existent
+    # submodule being restored (but with no content).
+    #
+    # This prevents restoration of the stash of the submodule index changes,
+    # which breaks pre-commit hook restorations of the working index.
+    #
+    # Thus we expose this helper so the restoration code can manually delete the
+    # directory.
+    #
+    # @raise [Overcommit::Exceptions::GitConfigError] when
+    def staged_submodule_removals
+      # There were no submodules before, so none could have been removed
+      return [] if `git ls-files .gitmodules`.empty?
+
+      previous = submodules(ref: 'HEAD')
+      current = submodules
+
+      previous - current
+    end
+
+    # Returns the current set of submodules.
+    #
+    # @param options [Hash]
+    # @return [Array<Overcommit::GitRepo::Submodule>]
+    def submodules(options = {})
+      ref = options[:ref]
+
+      modules = []
+      IniParse.parse(`git show #{ref}:.gitmodules`).each do |section|
+        modules << Submodule.new(section['path'], section['url'])
+      end
+
+      modules
+    rescue IniParse::IniParseError => ex
+      raise Overcommit::Exceptions::GitSubmoduleError,
+            "Unable to read submodule information from #{ref}:.gitmodules file: #{ex.message}"
+    end
   end
 end

overcommit.gemspec

@@ -27,6 +27,7 @@ Gem::Specification.new do |s|
   s.required_ruby_version = '>= 1.9.3'
 
   s.add_dependency             'childprocess', '~> 0.5.6'
+  s.add_dependency             'iniparse', '~> 1.4'
 
   s.add_development_dependency 'rspec', '~> 3.0'
   s.add_development_dependency 'travis', '~> 1.7'

spec/overcommit/git_repo_spec.rb

@@ -0,0 +1,67 @@
+require 'spec_helper'
+
+describe Overcommit::GitRepo do
+  describe '.staged_submodule_removals' do
+    subject { described_class.staged_submodule_removals }
+
+    around do |example|
+      submodule = repo do
+        `git commit --allow-empty -m "Submodule commit"`
+      end
+
+      repo do
+        `git submodule add #{submodule} sub-repo 2>&1 > /dev/null`
+        `git commit -m "Initial commit"`
+        example.run
+      end
+    end
+
+    context 'when there are no submodule removals staged' do
+      it { should be_empty }
+    end
+
+    context 'when there are submodule additions staged' do
+      before do
+        another_submodule = repo do
+          `git commit --allow-empty -m "Another submodule"`
+        end
+
+        `git submodule add #{another_submodule} another-sub-repo 2>&1 > /dev/null`
+      end
+
+      it { should be_empty }
+    end
+
+    context 'when there is one submodule removal staged' do
+      before do
+        `git rm sub-repo`
+      end
+
+      it 'returns the submodule that was removed' do
+        subject.size.should == 1
+        subject.first.tap do |sub|
+          sub.path.should == 'sub-repo'
+          File.directory?(sub.url).should == true
+        end
+      end
+    end
+
+    context 'when there are multiple submodule removals staged' do
+      before do
+        another_submodule = repo do
+          `git commit --allow-empty -m "Another submodule"`
+        end
+
+        `git submodule add #{another_submodule} yet-another-sub-repo 2>&1 > /dev/null`
+        `git commit -m "Add yet another submodule"`
+        `git rm sub-repo`
+        `git rm yet-another-sub-repo`
+      end
+
+      it 'returns all submodules that were removed' do
+        subject.size.should == 2
+        subject.map(&:path).sort.should == ['sub-repo', 'yet-another-sub-repo']
+      end
+    end
+  end
+end