tree e6d2cf19a3c4b5bbd48181f24271c7f7021f2158
parent 0f610c8b37c7d3305c9e504e7666f62c53508d3c
author David 'Digit' Turner <digit@google.com> 1643385413 +0100
committer Commit Bot <commit-bot@chromium.org> 1646854326 +0000

Introduce new built-in "phony" tool.

This CL is the first in a series that will allow GN to generate
smaller Ninja files, by using phone rules instead of stamp files
whenever possible. This is a split of the working proof-of-concept
available at https://gn-review.googlesource.com/c/gn/+/11380.

This CL does not change GN's behaviour but:

- It introduces the new BuiltinTool class used to expressed
  built-in toolchain tools that cannot be customized like "stamp"
  or "copy".

- It adds a single "phony" tool definition, and ensures it is
  added to each toolchain() instance automatically, but not
  listed when exporting the build graph to JSON.

  Note that nothing actually uses it at the moment, to make
  reviewing this CL easier.

- Add a new build settings flag, named "no_stamp_files". In
  the future, enabling it will allow generating phony rules
  instead of stamp files in Ninja outputs. For now, assert
  with an error message if it is set to avoid any misuse.

Note that Copyright notices mention 2020 because this work
was started a long time ago (thanks to rjascani@google.com's
work). They could be updated to 2022 without issues.

For testing the output of `gn gen` has been compared before
and after this CL was applied with the Fuchsia source tree
to verify that the output is the same.

Bug: 172
Change-Id: I8f1140d1d953d38c318e3def8a4ccf8bdc304d58
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/12864
Reviewed-by: Brett Wilson <brettw@google.com>
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>