commit 5b6c3d168d7f4481c5aae857c54a484e45b1d7e0
author Tyler Mandry <tmandry@google.com> Mon Mar 23 17:27:32 2020 -0700
committer Tyler Mandry <tmandry@google.com> Mon Mar 23 18:05:43 2020 -0700
tree 053f67828ee10fe4bf430c3061fd870f42e5e8d5
parent 0eaf3e591d403cd1d3637779a435c25ff3f7fdeb

[dart] Fix incremental builds when gn gen is run

write_file in GN does not touch the output file timestamp if the
contents of the file have changed. In this case however, write_file was
being evaluated at every step of a loop which built up the contents of
that file. Thus the contents of the file would change in every iteration
of the loop, and its timestamp would be updated unconditionally during
every call to `gn gen` as a result. Since this file was an input to
build steps, it caused a lot of targets to be rebuilt.

This change fixes that behavior, making GN-only changes in fuchsia
true no-ops when ninja is run. On my machine, this shaves off 44 seconds
of build time for GN-only changes.

Change-Id: Ie8a361eee03528812dda7ce535a6c86dc266664f