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# frozen_string_literal: true
module Gitlab
# Analyse a graph of commits from a push to a branch,
# for each commit, analyze that if it is the head of a merge request,
# then what should its merge_commit be, relative to the branch.
#
# A----->B----->C----->D target branch
# | ^
# | |
# +-->E----->F--+ merged branch
# | ^
# | |
# +->G--+
#
# (See merge-commit-analyze-after branch in gitlab-test)
#
# Assuming
# - A is already in remote
# - B~D are all in its own branch with its own merge request, targeting the target branch
#
# When D is finally pushed to the target branch,
# what are the merge commits for all the other merge requests?
#
# We can walk backwards from the HEAD commit D,
# and find status of its parents.
# First we determine if commit belongs to the target branch (i.e. A, B, C, D),
# and then determine its merge commit.
#
# +--------+-----------------+--------------+
# | Commit | Direct ancestor | Merge commit |
# +--------+-----------------+--------------+
# | D | Y | D |
# +--------+-----------------+--------------+
# | C | Y | C |
# +--------+-----------------+--------------+
# | F | | C |
# +--------+-----------------+--------------+
# | B | Y | B |
# +--------+-----------------+--------------+
# | E | | C |
# +--------+-----------------+--------------+
# | G | | C |
# +--------+-----------------+--------------+
#
# By examining the result, it can be said that
#
# - If commit is direct ancestor of HEAD, its merge commit is itself.
# - Otherwise, the merge commit is the same as its child's merge commit.
#
class BranchPushMergeCommitAnalyzer
class CommitDecorator < SimpleDelegator
attr_accessor :merge_commit
attr_writer :direct_ancestor # boolean
def direct_ancestor?
@direct_ancestor
end
# @param child_commit [CommitDecorator]
# @param first_parent [Boolean] whether `self` is the first parent of `child_commit`
def set_merge_commit(child_commit, first_parent:)
# If child commit is a direct ancestor, its first parent is also the direct ancestor.
# We assume direct ancestors matches the trail of the target branch over time,
# This assumption is correct most of the time, especially for gitlab managed merges,
# but there are exception cases which can't be solved (https://stackoverflow.com/a/49754723/474597)
@direct_ancestor = first_parent && child_commit.direct_ancestor?
@merge_commit = direct_ancestor? ? self : child_commit.merge_commit
end
end
# @param commits [Array] list of commits, must be ordered from the child (tip) of the graph back to the ancestors
def initialize(commits, relevant_commit_ids: nil)
@commits = commits
@id_to_commit = {}
@commits.each do |commit|
@id_to_commit[commit.id] = CommitDecorator.new(commit)
if relevant_commit_ids
relevant_commit_ids.delete(commit.id)
break if relevant_commit_ids.empty? # Only limit the analyze up to relevant_commit_ids
end
end
analyze
end
def get_merge_commit(id)
get_commit(id).merge_commit.id
end
private
def analyze
head_commit = get_commit(@commits.first.id)
head_commit.direct_ancestor = true
head_commit.merge_commit = head_commit
# Analyzing a commit requires its child commit be analyzed first,
# which is the case here since commits are ordered from child to parent.
@id_to_commit.each_value do |commit|
analyze_parents(commit)
end
end
def analyze_parents(commit)
commit.parent_ids.each.with_index do |parent_commit_id, i|
parent_commit = get_commit(parent_commit_id)
next if parent_commit.nil? # parent commit may not be part of new commits
parent_commit.set_merge_commit(commit, first_parent: i == 0)
end
end
def get_commit(id)
@id_to_commit[id]
end
end
end
|
