Gracefully handle large file lists in list_files helper

Previously, if the list of files was larger than the allowed number of
arguments for the OS, this would fail. Use our `execute` helper to
automatically handle argument splitting.

Author: sds

lib/overcommit/git_repo.rb

@@ -109,15 +109,16 @@ def modified_files(options)
     # @return [Array<String>] list of absolute file paths
     def list_files(paths = [], options = {})
       ref = options[:ref] || 'HEAD'
-      path_list =
-        if OS.windows?
-          paths = paths.map { |path| path.gsub('"', '""') }
-          paths.empty? ? '' : "\"#{paths.join('" "')}\""
-        else
-          paths.shelljoin
-        end
-      `git ls-tree --name-only #{ref} #{path_list}`.
-        split(/\n/).
+
+      result = Overcommit::Utils.execute(%W[git ls-tree --name-only #{ref}], args: paths)
+      unless result.success?
+        raise Overcommit::Exceptions::Error,
+              "Error listing files. EXIT STATUS(es): #{result.statuses}.\n" \
+              "STDOUT(s): #{result.stdouts}.\n" \
+              "STDERR(s): #{result.stderrs}."
+      end
+
+      result.stdout.split(/\n/).
         map { |relative_file| File.expand_path(relative_file) }.
         reject { |file| File.directory?(file) } # Exclude submodule directories
     end

spec/overcommit/git_repo_spec.rb

@@ -217,6 +217,20 @@
         end
       end
     end
+
+    context 'when the git ls-tree command fails for whatever reason' do
+      before do
+        result = double('result', success?: false, statuses: [1], stdouts: '', stderrs: '')
+        allow(Overcommit::Utils).
+          to receive(:execute).
+          with(%w[git ls-tree --name-only HEAD], args: []).
+          and_return(result)
+      end
+
+      it 'raises' do
+        expect { subject }.to raise_error Overcommit::Exceptions::Error
+      end
+    end
   end
 
   describe '.tracked?' do