Add helpful error messages to check_gn_headers.py

Add helpful error messages to check_gn_headers.py

Before running check_gn_headers.py, it is necessary to build all
in order to get the dependency info from the compiler. Directly
checking whether rebuilding is needed by running a build dry run
takes too long, so some heuristics are used instead.

BUG=661774
Review-Url: https://codereview.chromium.org/2891363004
Cr-Commit-Position: refs/heads/master@{#474588}
Committed: https://chromium.googlesource.com/chromium/src/+/0ceaba5ef538ce1780578d5e948641bc27f5829b

[wychen, 2017-05-19 16:04:25]

wychen@chromium.org changed reviewers:
+ dpranke@chromium.org, tfarina@chromium.org

[wychen, 2017-05-19 16:04:26]

PTAL

[Dirk Pranke, 2017-05-23 20:59:08]

I'm concerned by your description. I wouldn't want us to do anything that
actually was affecting the existing build directory, such that it might make the
build dirty or otherwise affect it.

Can we run gn gen into a temp directory instead?

[wychen, 2017-05-23 21:16:12]

On 2017/05/23 20:59:08, Dirk Pranke (slow) wrote:
> I'm concerned by your description. I wouldn't want us to do anything that
> actually was affecting the existing build directory, such that it might make
the
> build dirty or otherwise affect it.
> 
> Can we run gn gen into a temp directory instead?

I wasn't clear in the description.
The build directory becomes "dirty" in the sense of equivalent of touching
build.ninja without changing its content.

More on: http://crbug.com/724550

I have no idea what it takes to fix issue 724550, but I'll look into doing gn
gen elsewhere.

[wychen, 2017-05-23 22:40:17]

Description was changed from

==========
Add helpful error messages to check_gn_headers.py

Before running check_gn_headers.py, it is necessary to build all
in order to get the dependency info from the compiler. Directly
checking whether rebuilding is needed by running a build dry run
doesn't work because check_gn_headers.py calls "gn gen ...", which
touches some ninja files and make the build "dirty". Some heuristics
are used instead.

BUG=661774
==========

to

==========
Add helpful error messages to check_gn_headers.py

Before running check_gn_headers.py, it is necessary to build all
in order to get the dependency info from the compiler. Directly
checking whether rebuilding is needed by running a build dry run
takes too long, so some heuristics are used instead.

BUG=661774
==========

[wychen, 2017-05-23 22:58:52]

I revised it by preserving build.ninja. PTAL

Running "gn gen" elsewhere is more complicated because some generated files
wouldn't be there in the temp directory.

[Dirk Pranke, 2017-05-23 23:26:46]

On 2017/05/23 22:58:52, wychen wrote:
> I revised it by preserving build.ninja. PTAL

I don't think this is the right approach; it's still possible that `gn gen` will
otherwise modify something in the directory in a way we wouldn't like.

> Running "gn gen" elsewhere is more complicated because some generated files
> wouldn't be there in the temp directory.

Which files? I'm not following this part.

[wychen, 2017-05-23 23:53:00]

On 2017/05/23 23:26:46, Dirk Pranke (slow) wrote:
> On 2017/05/23 22:58:52, wychen wrote:
> > I revised it by preserving build.ninja. PTAL
> 
> I don't think this is the right approach; it's still possible that `gn gen`
will
> otherwise modify something in the directory in a way we wouldn't like.

You are right. It's more robust now.

> > Running "gn gen" elsewhere is more complicated because some generated files
> > wouldn't be there in the temp directory.
> 
> Which files? I'm not following this part.

This is addressed by manually replacing the OUT_DIR prefix.

[Dirk Pranke, 2017-05-25 01:43:35]

lgtm

[wychen, 2017-05-25 06:35:00]

The CQ bit was checked by wychen@chromium.org

[commit-bot: I haz the power, 2017-05-25 06:35:23]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-25 06:46:17]

CQ is committing da patch.

Bot data: {"patchset_id": 40001, "attempt_start_ts": 1495694100660110,
"parent_rev": "d1573db133006bac1f7f43a90b93be8e64b721de", "commit_rev":
"0ceaba5ef538ce1780578d5e948641bc27f5829b"}

[commit-bot: I haz the power, 2017-05-25 06:46:34]

Description was changed from

==========
Add helpful error messages to check_gn_headers.py

Before running check_gn_headers.py, it is necessary to build all
in order to get the dependency info from the compiler. Directly
checking whether rebuilding is needed by running a build dry run
takes too long, so some heuristics are used instead.

BUG=661774
==========

to

==========
Add helpful error messages to check_gn_headers.py

Before running check_gn_headers.py, it is necessary to build all
in order to get the dependency info from the compiler. Directly
checking whether rebuilding is needed by running a build dry run
takes too long, so some heuristics are used instead.

BUG=661774

Review-Url: https://codereview.chromium.org/2891363004
Cr-Commit-Position: refs/heads/master@{#474588}
Committed:
https://chromium.googlesource.com/chromium/src/+/0ceaba5ef538ce1780578d5e9486...
==========

[commit-bot: I haz the power, 2017-05-25 06:46:35]

Committed patchset #3 (id:40001) as
https://chromium.googlesource.com/chromium/src/+/0ceaba5ef538ce1780578d5e9486...

[tfarina, 2017-05-25 13:11:49]

lgtm, thanks.

[Moe, 2017-05-25 14:51:22]

A revert of this CL (patchset #3 id:40001) has been created in
https://codereview.chromium.org/2905863002/ by mahmadi@chromium.org.

The reason for reverting is: This CL is likely causing massive failures:

https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder/builds/8...
to
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder/builds/8...

and 

https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg...
to
https://build.chromium.org/p/chromium.linux/builders/Linux%20Builder%20%28dbg....