# Changelog

## 2.0.0 / 2026-02-01

This release has significant **breaking changes**.

- diff-lcs 2 supports Ruby 3.2 or higher. This allowed:

  - readability improvements (endless methods, pattern matching);

  - support for immutable Data classes (`Diff::LCS::Block`, `Diff::LCS::Change`,
    and `Diff::LCS::ContextChange`);

  - removal of compatibility shims;

  - reduction in conditional tests in loops, especially for String character
    extraction (compare `string ? seq[i, 1] : seq[i]` to `seq[i]`); and

  - optimizations to string and relying on standard encoding support present
    since Ruby 2.1.

  The primary API (methods and class methods on `Diff::LCS`) has not changed,
  with one exception noted below. Internal APIs (including `Diff::LCS::Block`,
  `Diff::LCS::Change`, `Diff::LCS::ContextChange`, and `Diff::LCS::Hunk`) have
  changed for compatibility.

- The `htmldiff` binary and supporting code have been removed without
  replacement.

- `ldiff` no longer supports `ed`-script output (`ed` and `reverse_ed` formats).
  As Baptiste Courtois says in [#108][pull-108], the "implementation was broken
  for a while and no-one reported it."

- The method `Diff::LCS.LCS` has been removed as an alias for `Diff::LCS.lcs`.
  Most callers are using `Diff::LCS.lcs` and modern Ruby did-you-mean support
  should assist with this update.

- `Diff::LCS::Change` objects implemented the comparison operator (`<=>`)
  incorrectly. Comparisons are now done so that the `position` is compared
  first, then the `action` (by index of `VALID_ACTIONS`), and finally the
  element. `Diff::LCS::ContextChange` works similarly, comparing the old and new
  positions prior to comparing the actions by index.

  The order of `VALID_ACTIONS` was changed for the index order to make sense.

- `ldiff` now implements `-` as a filename option for standard input. This is
  used for integration testing with RSpec like this:

  ```console
  rspec -Ilib -rdiff/lcs integration/failure/array_diff_spec.rb 2>&1 |
    ruby -Ilib bin/ldiff -U integration/golden/array_diff.txt -
  ```

- diff-lcs no longer uses RSpec as its test suite, but instead uses Minitest.
  The conversion to Minitest and the new RSpec integration tests
  (`rake integration`) were written with the assistance of [Kiro][kiro] and
  verified manually, with portions changed as required.

- The code of conduct was updated to the Contributor Covenant 3.0.

## 1.6.2 / 2025-05-12

- Handle upcoming changes to the `cgi` gem in Ruby 3.5 ([#147][pull-147])

- Fix issues found with `htmldiff` in Ruby 1.8 (which is used approximately
  never, since the code change which broke Ruby 1.8 was made 6 years ago).
  [#148][pull-148]

- Fixed some standardrb formatting and configuration issues.

## 1.6.1 / 2025-03-25

- Performed further work on `Diff::LCS::Ldiff` improvements ([#46][issue-46])
  and resolve several thread safety issues cleanly by making it a class.
  [#129][pull-129]

- Restructure the project to be more consistent with the rest of the projects
  that I manage.

- Increased GitHub action security.

- Added [trusted publishing][tp] for fully automated releases.

## 1.6.0 / 2025-02-13

- Baptiste Courtois ([@annih][gh-user-annih]) has done significant work on
  making `bin/ldiff` work better, contributing a number of issues and pull
  requests. These include:

  - Separation of command parsing from diff-generation in `Diff::LCS::Ldiff`
    code extraction making it easier to use separately from the `bin/ldiff`
    command in [#103][pull-103]. This partially resolves [#46][issue-46].

  - Improvement of binary and empty file detection and tests in [#104][pull-104]
    and [#105][pull-105]. This resolves issues [#100][issue-100],
    [#102][issue-102].

  - Various ldiff fixes for output [#101][pull-101] resolves issues
    [#106][issue-106] (ldiff ed scripts are inverted), [#107][issue-107] (ldiff
    hunk ranges are incorrect; regression or incorrect fix for [#60][issue-60]),
    and [#95][issue-95].

- Patrick Linnane fixed various minor typos. [#93][pull-93]

- Mark Young added a Changelog link to the RubyGems metadata. [#92][pull-92]
  This has been modified to incorporate it into the README.

- Updated the documentation on `Diff::LCS#lcs` to be clearer about the
  requirements for object equality comparison. This resolves [#70][issue-70].

- Governance:

  Changes described here are effective 2024-12-31.

  - Update gem management details to use markdown files for everything, enabled
    in part by [flavorjones/hoe-markdown][hoe-markdown]. Several files were
    renamed to be more consistent with standard practices.

  - Updated security notes with an [age][age] public key rather than pointing to
    Keybase.io and a PGP public key which I no longer use. The use of the
    [Tidelift security contact][tidelift] is recommended over direct disclosure.

## 1.5.1 / 2024-01-31

- Peter Goldstein updated CI configuration to add Ruby 3.1 and Masato Nakamura
  added Ruby 3.2 and 3.3. [#82][pull-82], [#89][pull-89]

- Switched to [standard ruby][standard ruby] formatting.

- Justin Steele converted the licence file to Markdown. [#84][pull-84]

- Updated the gem SPDX identifier for GPL 2.0 or later, resolving [#86][pull-86]
  by Vit Ondruch.

- Resolve a potential security issue with `ldiff` in its use of `IO.read`
  instead of `File.read`. [#91][issue-91]

- Added MFA authentication requirement for release to RubyGems. [#90][pull-90]

- Added Dependabot management for actions and gems. [#90][pull-90]

- Updated CodeQL configuration. [#90][pull-90]

## 1.5.0 / 2021-12-23

- Updated the CI configuration and monkey-patch Hoe.

- Kenichi Kamiya fixed a test configuration deprecation in SimpleCov.
  [#69][pull-69]

- Tien introduced several corrections and code improvements:

  - Removed an off-by-one error when calculating an index value by embracing
    Ruby iteration properly. This had a side-effect of fixing a long-standing
    bug in `#traverse_sequences` where the traversal would not be transitive.
    That is, `LCS(s2, s1)` should produce a sequence that is transitive with
    `LCS(s1, s2)` on traversal, and applying the diff computed from those
    results would result in equivalent changes that could be played forward or
    backward as appropriate. [#71][pull-71], [#75][pull-75]

  - The above fix resulted in a changed order of the longest common subsequence
    when callbacks were applied. After analysis, it was determined that the
    computed subsequence was _equivalent_ to the prior version, so the test was
    updated. This also resulted in the clarification of documentation when
    traversing the sub-sequences. [#79][pull-79]

  - An infinite loop case in the case where `Diff::LCS` would be included into
    an enumerable class has been fixed. [#73][pull-73]

  - Clarified the purpose of a threshold test in calculation of LCS.
    [#72][pull-72], [#80][pull-80]

- Removed autotest directory

## 1.4.4 / 2020-07-01

- Fixed an issue reported by Jun Aruga in the `Diff::LCS::Ldiff` binary text
  detection. [#44][issue-44]

- Fixed a theoretical issue reported by Jun Aruga in `Diff::LCS::Hunk` to raise
  a more useful exception. [#43][issue-43]

- Added documentation that should address custom object issues as reported in
  [#35][issue-35].

- Fixed more diff errors, in part reported in [#65][issue-65].

  - The use of `Numeric#abs` is incorrect in `Diff::LCS::Block#diff_size`. The
    diff size _must_ be accurate for correct change placement.

  - When selecting `@max_diff_size` in `Diff::LCS::Hunk`, choose it based on
    `block.diff_size.abs`.

  - Made a number of changes that will, unfortunately, increase allocations at
    the cost of being safe with frozen strings.

  - Add some knowledge that when `Diff::LCS::Hunk#diff` is called, that we are
    processing the _last_ hunk, so some changes will be made to how the output
    is generated.

    - `old`, `ed`, and `reverse_ed` formats have no differences.

    - `unified` format will report `\ No newline at end of file` given the
      correct conditions, at most once. Unified range reporting also differs for
      the last hunk such that the `length` of the range is reduced by one.

    - `context` format will report `\No newline at end of file` given the
      correct conditions, up to once per "file". Context range reporting also
      differs for the last hunk such that the `end` part of the range is reduced
      by one to a minimum of one.

- Added a bunch more tests for the cases above, and fixed `hunk_spec.rb` so that
  the phrase being compared isn't nonsense French.

- Updated formatting.

- Added a Rake task to assist with manual testing on Ruby 1.8.

## 1.4.3 / 2020-06-29

- Fixed several issues with 1.4 on Rubies older than 2.0. Some of this was
  providing useful shim functions to Hoe 3.x (which dropped these older Rubies a
  while ago). Specifically:

  - Removed Array#lazy from a method in `Diff::LCS::Hunk`.

  - Changed some unit tests to use old-style Symbol-keyed hashes.

  - Changed some unit test helper functions to no longer use keyword parameters,
    but only a trailing options hash.

  - Made the use of `psych` dependent on `RUBY_VERSION >= 1.9`.

  Resolves [#63][issue-63].

## 1.4.2 / 2020-06-23

- Camille Drapier fixed a small issue with RuboCop configuration. [#59][pull-59]

- Applied another fix (and unit test) to fix an issue for the Chef team.
  [#60][issue-60], [#61][pull-61]

## 1.4.1 / 2020-06-23

- Fix an issue where diff sizes could be negative, and they should be.
  [#57][issue-57], [#58][pull-58]

## 1.4 / 2020-06-23

- Ruby versions lower than 2.4 are soft-deprecated and will not be run as part
  of the CI process any longer.

- Akinora MUSHA (knu) added the ability for `Diff::LCS::Change` objects to be
  implicitly treated arrays. Originally provided as pull request [#47][pull-47],
  but it introduced a number of test failures as documented in [#48][issue-48],
  and remediation of `Diff::LCS` itself was introduced in [#49][pull-49].

- Resolved [#5][issue-05] with some tests comparing output from `system` calls
  to `bin/ldiff` with some pre-generated output. Resolved [#6][issue-06] with
  these tests.

- Resolved a previously undetected `bin/ldiff` issue with `--context` output not
  matching `diff --context` output.

- Resolved an issue with later versions of Ruby not working with an `OptParse`
  specification of `Numeric`; this has been changed to `Integer`.

- Brandon Fish added TruffleRuby in [#52][pull-52].

- Fixed two missing classes as reported in [#53][issue-53].

## 1.3 / 2017-01-18

- Bugs fixed:

  - Fixed an error for `bin/ldiff --version`. Fixes issue [#21][issue-21].

  - Force `Diff::LCS::Change` and `Diff::LCS::ContextChange` to only perform
    equality comparisons against themselves. Provided by Kevin Mook in pull
    request [#29][pull-29].

  - Fix tab expansion in `htmldiff`, provided by Mark Friedgan in pull request
    [#25][pull-25].

  - Silence Ruby 2.4 `Fixnum` deprecation warnings. Fixes issue [#38][issue-38]
    and pull request [#36][pull-36].

  - Ensure that test dependencies are loaded properly. Fixes issue
    [#33][issue-33] and pull request [#34][pull-34].

  - Fix issue [#1][issue-01] with incorrect intuition of patch direction.
    Tentative fix, but the previous failure cases pass now.

- Tooling changes:

  - Added SimpleCov and Coveralls support.

  - Change the homepage (temporarily) to the GitHub repo.

  - Updated testing and gem infrastructure.

  - Modernized the specs.

- Cleaned up documentation.

- Added a Code of Conduct.

## 1.2.5 / 2013-11-08

- Bugs fixed:

  - Comparing arrays flattened them too far, especially with `Diff::LCS.sdiff`.
    Fixed by Josh Bronson in pull request [#23][pull-23].

## 1.2.4 / 2013-04-20

- Bugs fixed:

  - A bug was introduced after 1.1.3 when pruning common sequences at the start
    of comparison. Paul Kunysch (@pck) fixed this in pull request
    [#18][pull-18]. Thanks!

  - The Rubinius (1.9 mode) bug in [rubinius/rubinius#2268][rubinius#2268] has
    been fixed by the Rubinius team two days after it was filed. Thanks for
    fixing this so quickly!

- Switching to Raggi's hoe-gemspec2 for gemspec generation.

## 1.2.3 / 2013-04-11

- Bugs Fixed:

  - The new encoding detection for diff output generation (added in 1.2.2)
    introduced a bug if the left side of the comparison was the empty set.
    Originally found in [rspec/rspec-expectations#238][rspec-expectations#238]
    and [rspec/rspec-expectations#239][rspec-expectations#239]. Jon Rowe
    developed a reasonable heuristic (left side, right side, empty string
    literal) to avoid this bug.

  - There is a known issue with Rubinius in 1.9 mode reported in
    [rubinius/rubinius#2268][rubinius#2268] and demonstrated in the Travis CI
    builds. For all other tested platforms, diff-lcs is considered stable. As
    soon as a suitably small test-case can be created for the Rubinius team to
    examine, this will be added to the Rubinius issue around this.

## 1.2.2 / 2013-03-30

- Bugs Fixed:

  - `Diff::LCS::Hunk` could not properly generate a difference for comparison
    sets that are not US-ASCII-compatible because of the use of literal regular
    expressions and strings. Jon Rowe found this in
    [rspec/rspec-expectations#219][rspec-expectations#219] and provided a first
    pass implementation in pull request [#15][pull-15]. I've reworked it because
    of test failures in Rubinius when running in Ruby 1.9 mode. This coerces the
    added values to the encoding of the old dataset (as determined by the first
    piece of the old dataset).

  - Adding Travis CI testing for Ruby 2.0.

## 1.2.1 / 2013-02-09

- Bugs Fixed:

  - As seen in [rspec/rspec-expectations#200][rspec-expectations#200], the
    release of `Diff::LCS` 1.2 introduced an unnecessary public API change to
    `Diff::LCS::Hunk` (see the change at
    [rspec/rspec-expectations@3d6fc82c][rspec-expectations@3d6fc82c] for
    details). The new method name (and behaviour) is more correct, but I should
    not have renamed the function or should have at least provided an alias.
    This release restores `Diff::LCS::Hunk#unshift` as an alias to #merge. Note
    that the old `#unshift` behaviour was incorrect and will not be restored.

## 1.2.0 / 2013-01-21

- Minor Enhancements:

  - Added special case handling for `Diff::LCS.patch` so that it handles patches
    that are empty or contain no changes.

  - Added two new methods (`#patch_me` and `#unpatch_me`) to the include-able
    module.

- Bugs Fixed:

  - Fixed issue [#1][issue-01] patch direction detection.

  - Resolved issue [#2][issue-02] by handling `string[string.size, 1]` properly
    (it returns `""` not `nil`).

  - Michael Granger (ged) fixed an implementation error in `Diff::LCS::Change`
    and added specs in pull request [#8][pull-08]. Thanks!

  - Made the code auto-testable.

  - Vít Ondruch (voxik) provided the latest version of the GPL2 license file in
    pull request [#10][pull-10]. Thanks!

  - Fixed a documentation issue with the include-able versions of `#patch!` and
    `#unpatch!` where they implied that they would replace the original value.
    Given that `Diff::LCS.patch` always returns a copy, the documentation was
    incorrect and has been corrected. To provide the behaviour that was
    originally documented, two new methods were added to provide this behaviour.
    Found by scooter-dangle in issue [#12][issue-12]. Thanks!

- Code Style Changes:

  - Removed trailing spaces.

  - Calling class methods using `.` instead of `::`.

  - Vít Ondruch (voxik) removed unnecessary shebangs in pull request
    [#9][pull-09]. Thanks!

  - Kenichi Kamiya (kachick) removed some warnings of an unused variable in
    lucky pull request [#13][pull-13]. Thanks!

  - Embarked on a major refactoring to make the files a little more manageable
    and understand the code on a deeper level.

  - Adding CI via Travis CI.

## 1.1.3 / 2011-08-27

- Converted to 'hoe' for release.

- Converted tests to RSpec 2.

- Extracted the body of `htmldiff` into a class available from
  `diff/lcs/htmldiff`.

- Migrated development and issue tracking to GitHub.

- Bugs fixed:

  - Eliminated the explicit use of RubyGems in both `bin/htmldiff` and
    `bin/ldiff`. Resolves issue [#4][issue-04].

  - Eliminated Ruby warnings. Resolves issue [#3][issue-03].

## 1.1.2 / 2004-10-20

- Fixed a problem reported by Mauricio Fernandez in `htmldiff`.

## 1.1.1 / 2004-09-25

- Fixed bug [#891][gh-issue-891] (Set returned from patch command does not
  contain last equal part).

- Fixed a problem with callback initialisation code (it assumed that all
  callbacks passed as classes can be initialised; now, it rescues NoMethodError
  in the event of private :new being called).

- Modified the non-initialisable callbacks to have a private `#new` method.

- Moved `ldiff` core code to `Diff::LCS::Ldiff` (`diff/lcs/ldiff.rb`).

## 1.1.0

- Eliminated the need for `Diff::LCS::Event` and removed it.

- Added a contextual diff callback, `Diff::LCS::ContextDiffCallback`.

- Implemented (un-)patching for standard diff callback output formats with both
  `#diff` and `#sdiff`.

- Extensive documentation changes.

## 1.0.4

- Fixed a problem with `bin/ldiff` output, especially for unified format.
  Newlines that should have been present weren't.

- Changed the `.tar.gz` installer to generate Windows batch files if ones do not
  exist already. Removed the existing batch files as they didn't work.

## 1.0.3

- Fixed a problem with `#traverse_sequences` where the first difference from the
  left sequence might not be appropriately captured.

## 1.0.2

- Fixed an issue with `ldiff` not working because actions were changed from
  symbols to strings.

## 1.0.1

- Minor modifications to the `gemspec`, the `README`.

- Renamed the diff program to `ldiff` (as well as the companion batch file) so
  as to not collide with the standard diff program.

- Fixed issues with RubyGems. Requires RubyGems > 0.6.1 or >= 0.6.1 with the
  latest CVS version.

## 1.0

- Initial release based mostly on Perl's Algorithm::Diff.

[age]: https://github.com/FiloSottile/age
[hoe-halostatue]: https://github.com/halostatue/hoe-halostatue
[hoe-markdown]: https://github.com/flavorjones/hoe-markdown
[issue-01]: https://github.com/halostatue/diff-lcs/issues/1
[issue-02]: https://github.com/halostatue/diff-lcs/issues/2
[issue-03]: https://github.com/halostatue/diff-lcs/issues/3
[issue-04]: https://github.com/halostatue/diff-lcs/issues/4
[issue-05]: https://github.com/halostatue/diff-lcs/issues/5
[issue-06]: https://github.com/halostatue/diff-lcs/issues/6
[issue-12]: https://github.com/halostatue/diff-lcs/issues/12
[issue-21]: https://github.com/halostatue/diff-lcs/issues/21
[issue-33]: https://github.com/halostatue/diff-lcs/issues/33
[issue-35]: https://github.com/halostatue/diff-lcs/issues/35
[issue-38]: https://github.com/halostatue/diff-lcs/issues/38
[issue-43]: https://github.com/halostatue/diff-lcs/issues/43
[issue-44]: https://github.com/halostatue/diff-lcs/issues/44
[issue-46]: https://github.com/halostatue/diff-lcs/issues/46
[issue-48]: https://github.com/halostatue/diff-lcs/issues/48
[issue-53]: https://github.com/halostatue/diff-lcs/issues/53
[issue-57]: https://github.com/halostatue/diff-lcs/issues/57
[issue-60]: https://github.com/halostatue/diff-lcs/issues/60
[issue-63]: https://github.com/halostatue/diff-lcs/issues/63
[issue-65]: https://github.com/halostatue/diff-lcs/issues/65
[issue-70]: https://github.com/halostatue/diff-lcs/issues/70
[issue-91]: https://github.com/halostatue/diff-lcs/issues/91
[issue-95]: https://github.com/halostatue/diff-lcs/issues/95
[issue-100]: https://github.com/halostatue/diff-lcs/issues/100
[issue-102]: https://github.com/halostatue/diff-lcs/issues/102
[issue-106]: https://github.com/halostatue/diff-lcs/issues/106
[issue-107]: https://github.com/halostatue/diff-lcs/issues/107
[pull-08]: https://github.com/halostatue/diff-lcs/pull/8
[pull-09]: https://github.com/halostatue/diff-lcs/pull/9
[pull-10]: https://github.com/halostatue/diff-lcs/pull/10
[pull-13]: https://github.com/halostatue/diff-lcs/pull/13
[pull-15]: https://github.com/halostatue/diff-lcs/pull/15
[pull-18]: https://github.com/halostatue/diff-lcs/pull/18
[pull-23]: https://github.com/halostatue/diff-lcs/pull/23
[pull-25]: https://github.com/halostatue/diff-lcs/pull/25
[pull-29]: https://github.com/halostatue/diff-lcs/pull/29
[pull-34]: https://github.com/halostatue/diff-lcs/pull/34
[pull-36]: https://github.com/halostatue/diff-lcs/pull/36
[pull-47]: https://github.com/halostatue/diff-lcs/pull/47
[pull-49]: https://github.com/halostatue/diff-lcs/pull/49
[pull-52]: https://github.com/halostatue/diff-lcs/pull/52
[pull-58]: https://github.com/halostatue/diff-lcs/pull/58
[pull-59]: https://github.com/halostatue/diff-lcs/pull/59
[pull-61]: https://github.com/halostatue/diff-lcs/pull/61
[pull-69]: https://github.com/halostatue/diff-lcs/pull/69
[pull-71]: https://github.com/halostatue/diff-lcs/pull/71
[pull-72]: https://github.com/halostatue/diff-lcs/pull/72
[pull-73]: https://github.com/halostatue/diff-lcs/pull/73
[pull-75]: https://github.com/halostatue/diff-lcs/pull/75
[pull-79]: https://github.com/halostatue/diff-lcs/pull/79
[pull-80]: https://github.com/halostatue/diff-lcs/pull/80
[pull-82]: https://github.com/halostatue/diff-lcs/pull/82
[pull-84]: https://github.com/halostatue/diff-lcs/pull/84
[pull-86]: https://github.com/halostatue/diff-lcs/pull/86
[pull-89]: https://github.com/halostatue/diff-lcs/pull/89
[pull-90]: https://github.com/halostatue/diff-lcs/pull/90
[pull-92]: https://github.com/halostatue/diff-lcs/pull/92
[pull-93]: https://github.com/halostatue/diff-lcs/pull/93
[pull-101]: https://github.com/halostatue/diff-lcs/pull/101
[pull-103]: https://github.com/halostatue/diff-lcs/pull/103
[pull-104]: https://github.com/halostatue/diff-lcs/pull/104
[pull-105]: https://github.com/halostatue/diff-lcs/pull/105
[pull-108]: https://github.com/halostatue/diff-lcs/pull/108
[pull-129]: https://github.com/halostatue/diff-lcs/pull/129
[pull-147]: https://github.com/halostatue/diff-lcs/pull/147
[pull-148]: https://github.com/halostatue/diff-lcs/pull/148
[rspec-expectations#200]: https://github.com/rspec/rspec-expectations/pull/200
[rspec-expectations#219]: https://github.com/rspec/rspec-expectations/issues/219
[rspec-expectations#238]: https://github.com/rspec/rspec-expectations/issues/238
[rspec-expectations#239]: https://github.com/rspec/rspec-expectations/issues/239
[rspec-expectations@3d6fc82c]: https://github.com/rspec/rspec-expectations/commit/3d6fc82c
[rubinius#2268]: https://github.com/rubinius/rubinius/issues/2268
[standard ruby]: https://github.com/standardrb/standard
[tidelift]: https://tidelift.com/security
[tp]: https://guides.rubygems.org/trusted-publishing/
[kiro]: https://kiro.dev
[gh-user-annih]: https://github.com/annih
[gh-issue-891]: https://github.com/halostatue/diff-lcs/issues/891
