reproducible engine build

[jwinarske]

Requirement is to support a reproducible engine library.

This means the file can be compared to prior build, and there is not difference.

The solution revolves around removal of .git folders and any processes dependent on the .git folder.

Round 1

gclient sync --revision ada363ee93b17cfe31587b5102679885cb40837e --no-history --shallow
find . -name .git -type d -print0|xargs -0 rm -r --
./flutter/tools/gn --unoptimized --no-goma

It fails with

Generating GN files in: out/host_debug_unopt
ERROR at //flutter/shell/version/version.gni:17:7: Script returned non-zero exit code.
      exec_script("//flutter/build/git_revision.py",
      ^----------
Current dir: /mnt/raid10/flutter-engine/src/out/host_debug_unopt/
Command: vpython3 /mnt/raid10/flutter-engine/src/flutter/build/git_revision.py --repository /mnt/raid10/flutter-engine/src/flutter
Returned 1.
stderr:

fatal: not a git repository (or any parent up to mount point /mnt)
Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
Traceback (most recent call last):
  File "/mnt/raid10/flutter-engine/src/flutter/build/git_revision.py", line 58, in <module>
    sys.exit(main())
  File "/mnt/raid10/flutter-engine/src/flutter/build/git_revision.py", line 51, in main
    version = get_repository_version(repository)
  File "/mnt/raid10/flutter-engine/src/flutter/build/git_revision.py", line 28, in get_repository_version
    version = subprocess.check_output([
  File "/home/joel/depot_tools/.cipd_bin/3.8/lib/python3.8/subprocess.py", line 415, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/home/joel/depot_tools/.cipd_bin/3.8/lib/python3.8/subprocess.py", line 516, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['git', '-C', '/mnt/raid10/flutter-engine/src/flutter', 'rev-parse', 'HEAD']' returned non-zero exit status 128.

See //flutter/tools/path_ops/BUILD.gn:5:1: whence it was imported.
import("//flutter/shell/version/version.gni")
^-------------------------------------------
See //flutter/BUILD.gn:93:9: which caused the file to be included.
        "//flutter/tools/path_ops",
        ^-------------------------

I update flutter/build/git_revision.py to return value of the engine I just pulled:

def get_repository_version(repository):
  return 'ada363ee93b17cfe31587b5102679885cb40837e'

./flutter/tools/gn --unoptimized --no-goma returns without error.

Build attempt fails with:

 ./flutter/tools/gn --unoptimized --no-goma --no-prebuilt-dart-sdk
Generating GN files in: out/host_debug_unopt
Generating compile_commands took 25ms
Done. Made 1276 targets from 349 files in 946ms
[joel@air src]$ ninja -C out/host_debug_unopt
ninja: Entering directory `out/host_debug_unopt'
[0/1] Regenerating ninja files
...
[0/1] Regenerating ninja files
ninja: error: manifest 'build.ninja' still dirty after 100 tries

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