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# 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# outdated, and we will display that fact to the user.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
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