# Monorepo History Pruning These are the steps we will/did follow to prune excessive history from the [flutter/engine](https://github.com/flutter/engine) repository when we merged with [flutter/flutter](https://github.com/flutter/flutter). The idea was to retain as much useful history as possible without blowing up the footprint of the framework's `.git` folder. The history that should get merged should be as relative and useful to currently engine development. The engine `.git` folder is ~780MB of history. * Binary files were checked in that are not used anymore. * Third party librariers were checked in and removed nearly a decade ago. * Examples were created and later moved elsewhere. ## Step 1: Fresh Clone + Safety Do not start with your working tree. Remove the origin so we don't mess with the `flutter/engine`. ```shell ############################################## ## Do some cleanup work on the engine and get ## the folder structure right. ############################################## # clone the repo to a fresh working folder git clone git@github.com:flutter/engine.git engine_prep cd engine_prep # for saftey - remove the remote - we're going to edit history git remote remove origin ``` ### Optional - Analyze the repo If you want to analyze the repository, you should intall [git filter-repo](http://github.com/newren/git-filter-repo) on your path and then run: ```shell # Analyze if you want, just remember to remove .git/filter-repo git filter-repo --analyze --force ``` The output is stored in `.git/filter-repo`. ## Step 2: Prune the History The following table is pulled from git-filter-repo's analsis. The `Packed Size` due to cross referencing. In general; we looked at large files that are not referenced any more and folders older than 2016. | Packed Size | Deleted Date | Path | Notes | |-------------|:-------------|:----------------------------------------|:-----------------------------| | 112784745 | 2024-05-13 | ci/licenses_golden/licenses_third_party | | | 27531902 | ~2021 | *.jar | binary | | 27379931 | 2016-08-09 | third_party/android_platform | android_platform and webview | | 27000000 | 2024-07-15 | impeller/docs/assets/*.(png|gif) | moved to another repository | | 15121375 | 2023-02-13 | *.ttc | font files | | 10104182 | 2023-02-13 | */SourceHanSerifCN* | | | 7985682 | 2018-08-08 | travis | old ci | | 6315637 | 2015-11-07 | examples/game | | | 3939429 | 2015-07-28 | sky/sdk | | | 3939429 | 2015-07-28 | sky/packages/sky | | | 3903787 | 2016-08-09 | mojo | | | 3686830 | 2022-06-14 | testing/scenario_app/android/reports | | | 3188930 | 2015-06-30 | tests/fast | | | 3173966 | 2015-08-07 | */example/game* | | | 2018961 | 2016-08-09 | third_party/libxml | | | 1804199 | 2016-08-09 | third_party/tcmalloc | | | 1393936 | ~2016 | *.dll | binary | | 1373740 | 2017-07-06 | tests/data | | | 1100665 | 2015-06-27 | benchmarks/parser/resources/html5.html | | | 1059673 | 2015-07-20 | third_party/protobuf | | | 978870 | 2022-04-27 | impeller/third_party | | | 798852 | 2015-07-20 | third_party/cython | | | 778560 | 2022-01-24 | lib/web_ui/test/golden_files | | | 634455 | 2016-08-09 | third_party/libpng | | | 610751 | 2024-05-13 | .golden | | | 550475 | 2024-09-17 | impeller/fixtures/flutter_logo_baked.* | | | 526837 | 2016-08-09 | third_party/libevent | | | 523436 | 2015-07-20 | third_party/boringssl | | | 514968 | 2022-04-27 | impeller/fixtures/image.png | | | 461527 | 2015-12-11 | third_party/re2 | | | 418122 | 2015-10-12 | examples/demo_launcher | | | 413787 | 2015-11-07 | .aac | | | 362787 | 2016-08-09 | third_party/glfw | | | 349604 | 2016-08-09 | third_party/harfbuzz-ng | | | 340869 | 2016-08-09 | third_party/okhttp | | | 321659 | 2016-08-09 | .S | | | 300824 | 2016-08-09 | .so | | | 257633 | 2016-08-09 | third_party/libjpeg | | | 257519 | 2016-08-09 | third_party/jinja2 | | | 249618 | 2016-08-09 | third_party/zlib | | | 218643 | 2015-12-11 | third_party/brotli | | | 188622 | 2021-01-06 | .idl | | | 184593 | 2015-09-02 | third_party/khronos | | | 173210 | 2016-08-09 | .gypi | | | 170484 | 2016-08-09 | third_party/expat | | | 169578 | 2016-08-09 | .asm | | | 161360 | 2016-08-09 | .m4 | | | 142670 | 2018-05-10 | .in | | | 140364 | 2015-12-11 | third_party/ots | | | 137270 | 2016-08-09 | .hh | | | 136787 | 2016-08-09 | .gyp | | | 99503 | 2016-08-09 | third_party/qcms | | | 91730 | 2015-08-21 | .pxd | | | 84850 | 2016-08-09 | third_party/yasm | | The following command will remove files and foldes from the checkout history. Since this is a destructive edit, the SHA1 git hashes will be changed in the process. At the end, the `.git` history will be 74 MB of object files. ```shell # Lets do some heavy filtering; # .git starts out at ~780MB and ends up at ~110MB git filter-repo --force --invert-paths \ --path-glob 'impeller/docs/assets/*.png' \ --path-glob 'impeller/docs/assets/*.gif' \ --path-glob '*/example/game/*' \ --path-glob 'benchmarks/parser/resources/html5.html' \ --path-glob '*.dll' \ --path-glob '*.jar' \ --path-glob '*/SourceHanSerifCN*' \ --path-glob 'third_party/txt/third_party/fonts/NotoSansCJK-Regular.ttc' \ --path-glob 'impeller/fixtures/flutter_logo_baked.*' \ --path-glob 'impeller/fixtures/image.png' \ --path-glob '*.golden' \ --path-glob '*.aac' \ --path-glob '*.S' \ --path-glob '*.so' \ --path-glob '*.idl' \ --path-glob '*.gpy' \ --path-glob '*.gypi' \ --path-glob '*.asm' \ --path-glob '*.m4' \ --path-glob '*.in' \ --path-glob '*.pxd' \ --path-glob '*.hh' \ --path 'ci/licenses_golden/licenses_third_party' \ --path 'testing/scenario_app/android/reports' \ --path 'impeller/third_party' \ --path 'mojo/public/third_party' \ --path 'tests/data' \ --path 'tests/fast' \ --path 'tests/framework' \ --path 'travis' \ --path 'mojo' \ --path 'sky/sdk' \ --path 'sky/engine' \ --path 'sky/tools/webkitpy' \ --path 'sky/shell' \ --path 'sky/packages/sky' \ --path 'sky/tests' \ --path 'sky/unit' \ --path 'sky/services' \ --path 'sky/compositor' \ --path 'sky/build' \ --path 'sky/specs' \ --path 'skysprites' \ --path 'examples/demo_launcher' \ --path 'examples/game' \ --path 'third_party/qcms' \ --path 'third_party/libevent' \ --path 'third_party/boringssl' \ --path 'third_party/tcmalloc' \ --path 'third_party/cython' \ --path 'third_party/protobuf' \ --path 'third_party/libpng' \ --path 'third_party/re2' \ --path 'third_party/harfbuzz-ng' \ --path 'third_party/jinja2' \ --path 'third_party/libjpeg' \ --path 'third_party/glfw' \ --path 'third_party/zlib' \ --path 'third_party/android_platform' \ --path 'third_party/expat' \ --path 'third_party/brotli' \ --path 'third_party/yasm' \ --path 'third_party/khronos' \ --path 'third_party/okhttp' \ --path 'third_party/libxml' \ --path 'third_party/ots' \ --path 'third_party/libXNVCtrl' \ --path 'lib/web_ui/test/golden_files' \ --path 'apk' \ --path 'flutter' \ --path 'base' \ --path 'sdk' \ --path 'gpu' \ --path 'engine' \ --path 'tools/webkitpy' \ --path 'tools/valgrind' \ --path 'tools/clang' \ --path 'tools/android' \ --path 'build/linux' \ --path 'build/win' \ --path 'build/mac' \ --path 'ui' \ --path 'examples/stocks' \ --path 'examples/stocks2' \ --path 'examples/stocks-fn' \ --path 'examples/data' \ --path 'examples/fitness' \ --path 'examples/city-list' \ --path 'examples/widgets' \ --path 'examples/raw' \ --path 'examples/color' \ --path 'examples/flights' \ --path 'examples/rendering' \ --path 'examples/fn' \ --path 'specs' \ --path 'url' \ --path 'services' \ --path 'framework' \ --path 'crypto' \ --path 'skia/ext' \ --path 'e2etests' \ --path 'tests/resources' \ --path 'viewer' \ --path 'lib/stub_ui' \ --path 'content_handler' # Garbage collect! git reflog expire --expire=now --all && git gc --prune=now --aggressive ``` ## Step 3 - Rewirte directories The final destination for the engine source code will be in the directory `engine/src/flutter` *except* for `DEPS` which remains at the root. Using `git mv` only affects HEAD and can have some problems when logging. Instead we'll re-write history so it makes sense in the new world. ```shell # Move files to engine/src/flutter, update tags so they don't collide, and move DEPS back to root. git filter-repo --to-subdirectory-filter engine/src/flutter --tag-rename '':'engine-' --force git filter-repo --path-rename engine/src/flutter/DEPS:DEPS ``` ## Step 4 - Rewrite the PR links The PR link in the first line of the comment message will be wrong; `flutter/flutter` doesn't have the same history. To make history a little bit better, we only want to edit the first line. This must be done before we merge with the `flutter/flutter` repo so as not to step on their commit lines. ```shell git filter-repo --force --message-callback ' return re.sub(br"^(.*)\((#\d+)\)\n(.*)", br"\1(flutter/engine\2)\n\3", message, 1) ' ``` ## Execute Order 42: Merge The Repositories ```shell ############################################## ## Now handle merging into flutter/flutter ############################################## git clone git@github.com:flutter/flutter.git flutter_merge cd flutter_merge # add the other tree as remote git remote add -f engine-upstream ~/src/engine_prep # --no-commit is important because we want to look around git merge --no-commit --allow-unrelated-histories engine-upstream/main # You're a wizard, Harry git commit -m "Merge flutter/engine into framework" # Garbage collect! # Now at 234MB .git git reflog expire --expire=now --all && git gc --prune=now --aggressive ```