Fix push after pull with full history rewrite

bin/git-subrepo

@@ -7,5 +7,11 @@ require "subrepo/version"
 
 app = Subrepo::CLI.new
 app.setup
-result = app.run(ARGV)
+begin
+  result = app.run(ARGV)
+rescue => e
+  require 'pry'
+  binding.pry
+end
+
 exit result

lib/subrepo/commands.rb

@@ -133,6 +133,19 @@ def command_pull(subdir, squash:, remote: nil)
       end
     end
 
+    # Push subrepo to the remote
+    #
+    # Steps in the process:
+    #
+    # * Fetch latest state from remote
+    # * Abort if any changes on the remote were not known: In this case, we
+    #   need to pull first
+    # * Map the entire history of the repository, keeping only changes relevant
+    #   to the subrepo
+    # * Rebase the mapped history onto the latest fetched commit
+    # * Push the result
+    # * Record the pushed commit and its local equivalent in the subrepo
+    #   configuration
     def command_push(subdir, remote: nil, branch: nil)
       subdir or raise "No subdir provided"
       fetched = command_fetch(subdir, remote: remote)
@@ -142,7 +155,7 @@ def command_push(subdir, remote: nil, branch: nil)
       config = Config.new(subdir)
 
       remote ||= config.remote
-      branch ||= config.branch
+      target_branch ||= config.branch
       last_merged_commit = config.commit
       last_pushed_commit = config.parent
 
@@ -158,9 +171,41 @@ def command_push(subdir, remote: nil, branch: nil)
         raise "It seems #{split_branch_name} already exists. Remove it first"
       end
 
-      last_commit = map_commits(repo, subdir, last_pushed_commit, last_merged_commit)
+      # TODO: If last_merged_commit maps to last_pushed_commit,
+      # use mapped_commits(repo, subdir, last_pushed_commit,
+      # last_merged_commit) directly to avoid history rewrite.
 
-      unless last_commit
+      mapped_commit_sha = map_commits(repo, subdir, nil, nil)
+      require 'pry'
+      binding.pry
+
+      if last_merged_commit.empty?
+        last_commit_sha = mapped_commit_sha
+      else
+        mapped_commit = repo.lookup mapped_commit_sha
+        upstream_commit = repo.lookup last_merged_commit
+        committer = {
+          name: repo.config["user.name"],
+          email: repo.config["user.email"]
+        }
+        rebase = Rugged::Rebase.new(repo, mapped_commit, upstream_commit)
+        while (result = rebase.next())
+          # NOTE: Expect result to contain the in-memory index
+          #index = rebase.inmemory_index
+          # NOTE: We would like to do some conflict resolution here, i.e.,
+          # start a merge editor, but the in-memory index has the wrong owner
+          # so can't find its repo.
+          #raise if index.conflicts?
+
+          # NOTE: Some conflicts are trivial!
+          require 'pry'
+          binding.pry
+          last_commit_sha = rebase.commit(committer: committer)
+        end
+        rebase.finish(committer)
+      end
+
+      unless last_commit_sha
         if fetched
           warn "No changes to push"
         else
@@ -169,17 +214,20 @@ def command_push(subdir, remote: nil, branch: nil)
         return
       end
 
-      repo.branches.create split_branch_name, last_commit
-      system "git push \"#{remote}\" #{split_branch_name}:#{branch}"
-      pushed_commit = last_commit
+      require 'pry'
+      binding.pry
+      repo.branches.create split_branch_name, last_commit_sha
+      system "git push \"#{remote}\" #{split_branch_name}:#{target_branch}"
 
       system "git branch -D #{split_branch_name}"
       parent_commit = `git rev-parse HEAD`.chomp
 
-      config.commit = pushed_commit
+      config.commit = last_commit_sha
       config.parent = parent_commit
       system "git add -f -- #{config.file_name}"
       system "git commit -m \"Push subrepo #{subdir}\""
+      require 'pry'
+      binding.pry
     end
 
     def command_init(subdir, remote: nil, branch: nil, method: nil)
@@ -280,7 +328,7 @@ def map_commits(repo, subdir, last_pushed_commit, last_merged_commit)
         target_parents = target_parent_shas.map { |sha| repo.lookup sha }
         rewritten_tree = calculate_subtree(repo, subdir, commit)
 
-        if parents.empty?
+        if target_parents.empty?
           next if rewritten_tree.entries.empty?
         else
           # TODO: Compare tree oids directly instead of doing a full diff