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| -rw-r--r-- | lib/gitlab/diff/position_tracer.rb | 168 |
1 files changed, 168 insertions, 0 deletions
diff --git a/lib/gitlab/diff/position_tracer.rb b/lib/gitlab/diff/position_tracer.rb new file mode 100644 index 00000000000..4d04f867268 --- /dev/null +++ b/lib/gitlab/diff/position_tracer.rb @@ -0,0 +1,168 @@ +# Finds the diff position in the new diff that corresponds to the same location +# specified by the provided position in the old diff. +module Gitlab + module Diff + class PositionTracer + attr_accessor :repository + attr_accessor :old_diff_refs + attr_accessor :new_diff_refs + attr_accessor :paths + + def initialize(repository:, old_diff_refs:, new_diff_refs:, paths: nil) + @repository = repository + @old_diff_refs = old_diff_refs + @new_diff_refs = new_diff_refs + @paths = paths + end + + def trace(old_position) + return unless old_diff_refs.complete? && new_diff_refs.complete? + return unless old_position.diff_refs == old_diff_refs + + # Suppose we have an MR with source branch `feature` and target branch `master`. + # When the MR was created, the head of `master` was commit A, and the + # head of `feature` was commit B, resulting in the original diff A->B. + # Since creation, `master` was updated to C. + # Now `feature` is being updated to D, and the newly generated MR diff is C->D. + # It is possible that C and D are direct decendants of A and B respectively, + # but this isn't necessarily the case as rebases and merges come into play. + # + # Suppose we have a diff note on the original diff A->B. Now that the MR + # is updated, we need to find out what line in C->D corresponds to the + # line the note was originally created on, so that we can update the diff note's + # records and continue to display it in the right place in the diffs. + # If we cannot find this line in the new diff, this means the diff note is now + # outdated, and we will display that fact to the user. + # + # In the new diff, the file the diff note was originally created on may + # have been renamed, deleted or even created, if the file existed in A and B, + # but was removed in C, and restored in D. + # + # Every diff note stores a Position object that defines a specific location, + # identified by paths and line numbers, within a specific diff, identified + # by start, head and base commit ids. + # + # For diff notes for diff A->B, the position looks like this: + # Position + # base_sha - ID of commit A + # head_sha - ID of commit B + # old_path - path as of A (nil if file was newly created) + # new_path - path as of B (nil if file was deleted) + # old_line - line number as of A (nil if file was newly created) + # new_line - line number as of B (nil if file was deleted) + # + # We can easily update `base_sha` and `head_sha` to hold the IDs of commits C and D, + # but need to find the paths and line numbers as of C and D. + # + # If the file was unchanged or newly created in A->B, the path as of D can be found + # by generating diff B->D ("head to head"), finding the diff file with + # `diff_file.old_path == position.new_path`, and taking `diff_file.new_path`. + # The path as of C can be found by taking diff C->D, finding the diff file + # with that same `new_path` and taking `diff_file.old_path`. + # The line number as of D can be found by using the LineMapper on diff B->D + # and providing the line number as of B. + # The line number as of C can be found by using the LineMapper on diff C->D + # and providing the line number as of D. + # + # If the file was deleted in A->B, the path as of C can be found + # by generating diff A->C ("base to base"), finding the diff file with + # `diff_file.old_path == position.old_path`, and taking `diff_file.new_path`. + # The path as of D can be found by taking diff C->D, finding the diff file + # with that same `old_path` and taking `diff_file.new_path`. + # The line number as of C can be found by using the LineMapper on diff A->C + # and providing the line number as of A. + # The line number as of D can be found by using the LineMapper on diff C->D + # and providing the line number as of C. + + results = nil + results ||= trace_added_line(old_position) if old_position.added? || old_position.unchanged? + results ||= trace_removed_line(old_position) if old_position.removed? || old_position.unchanged? + + return unless results + + file_diff, old_line, new_line = results + + Position.new( + old_path: file_diff.old_path, + new_path: file_diff.new_path, + head_sha: new_diff_refs.head_sha, + start_sha: new_diff_refs.start_sha, + base_sha: new_diff_refs.base_sha, + old_line: old_line, + new_line: new_line + ) + end + + private + + def trace_added_line(old_position) + file_path = old_position.new_path + + return unless diff_head_to_head + + file_head_to_head = diff_head_to_head.find { |diff_file| diff_file.old_path == file_path } + + file_path = file_head_to_head.new_path if file_head_to_head + + new_line = LineMapper.new(file_head_to_head).old_to_new(old_position.new_line) + + return unless new_line + + file_diff = new_diffs.find { |diff_file| diff_file.new_path == file_path } + return unless file_diff + + old_line = LineMapper.new(file_diff).new_to_old(new_line) + + [file_diff, old_line, new_line] + end + + def trace_removed_line(old_position) + file_path = old_position.old_path + + return unless diff_base_to_base + + file_base_to_base = diff_base_to_base.find { |diff_file| diff_file.old_path == file_path } + + file_path = file_base_to_base.old_path if file_base_to_base + + old_line = LineMapper.new(file_base_to_base).old_to_new(old_position.old_line) + + return unless old_line + + file_diff = new_diffs.find { |diff_file| diff_file.old_path == file_path } + return unless file_diff + + new_line = LineMapper.new(file_diff).old_to_new(old_line) + + [file_diff, old_line, new_line] + end + + def diff_base_to_base + @diff_base_to_base ||= diff_files(old_diff_refs.base_sha || old_diff_refs.start_sha, new_diff_refs.base_sha || new_diff_refs.start_sha) + end + + def diff_head_to_head + @diff_head_to_head ||= diff_files(old_diff_refs.head_sha, new_diff_refs.head_sha) + end + + def new_diffs + @new_diffs ||= diff_files(new_diff_refs.start_sha, new_diff_refs.head_sha, use_base: true) + end + + def diff_files(start_sha, head_sha, use_base: false) + base_sha = self.repository.merge_base(start_sha, head_sha) || start_sha + + diffs = self.repository.raw_repository.diff( + use_base ? base_sha : start_sha, + head_sha, + {}, + *paths + ) + + diffs.decorate! do |diff| + Gitlab::Diff::File.new(diff, repository: self.repository) + end + end + end + end +end |