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