Add a make target for generating Ctags file

Add a make target for generating Ctags file

This is very similar to the existing rule for a GTAGS file, and reuses
parts of it (the gtags.files file).

R=ahaas@chromium.org, mstarzinger@chromium.org, titzer@chromium.org
BUG=

Committed: https://crrev.com/79b1ab61c2a88fe740c94ffbb94bb5ac9ae17f40
Cr-Commit-Position: refs/heads/master@{#35435}

[Michael Starzinger, 2016-04-11 17:48:37]

mstarzinger@chromium.org changed reviewers:
+ jkummerow@chromium.org

[Michael Starzinger, 2016-04-11 17:48:38]

Forwarding this to Jakob, our resident Makefile wizard.

[Jakob Kummerow, 2016-04-11 18:43:24]

LGTM, but can you explain why the "wildcards" function is needed? AFAICT the
contents of gtags.files won't contain any wildcards anyway, so why would we have
to expand them?

[Clemens Hammacher, 2016-04-12 07:30:39]

On 2016/04/11 at 18:43:24, jkummerow wrote:
> LGTM, but can you explain why the "wildcards" function is needed? AFAICT the
contents of gtags.files won't contain any wildcards anyway, so why would we have
to expand them?

The wildcard filters out non-existing files, which otherwise would cause the
make process to fail because it does not know how to "generate" the missing
files.
Missing files still present in the gtags.files happen for example when you
switch branches.

[Jakob Kummerow, 2016-04-12 10:37:55]

On 2016/04/12 07:30:39, Clemens Hammacher wrote:
> On 2016/04/11 at 18:43:24, jkummerow wrote:
> > LGTM, but can you explain why the "wildcards" function is needed? AFAICT the
> contents of gtags.files won't contain any wildcards anyway, so why would we
have
> to expand them?
> 
> The wildcard filters out non-existing files, which otherwise would cause the
> make process to fail because it does not know how to "generate" the missing
> files.
> Missing files still present in the gtags.files happen for example when you
> switch branches.

OK, thanks for clarifying. Can you please add that as a comment to the Makefile?
E.g. right before line 500:

# Using $(wildcard ...) gracefully ignores non-existing files, so that stale
# gtags.files after switching branches don't cause recipe failures.

[Clemens Hammacher, 2016-04-12 15:21:30]

On 2016/04/12 at 10:37:55, jkummerow wrote:
> On 2016/04/12 07:30:39, Clemens Hammacher wrote:
> > On 2016/04/11 at 18:43:24, jkummerow wrote:
> > > LGTM, but can you explain why the "wildcards" function is needed? AFAICT
the
> > contents of gtags.files won't contain any wildcards anyway, so why would we
have
> > to expand them?
> > 
> > The wildcard filters out non-existing files, which otherwise would cause the
> > make process to fail because it does not know how to "generate" the missing
> > files.
> > Missing files still present in the gtags.files happen for example when you
> > switch branches.
> 
> OK, thanks for clarifying. Can you please add that as a comment to the
Makefile? E.g. right before line 500:
> 
> # Using $(wildcard ...) gracefully ignores non-existing files, so that stale
> # gtags.files after switching branches don't cause recipe failures.

Done.

[Jakob Kummerow, 2016-04-12 16:22:59]

Thanks, still LGTM.

[Clemens Hammacher, 2016-04-13 09:00:41]

The CQ bit was checked by clemensh@chromium.org

[commit-bot: I haz the power, 2016-04-13 09:00:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1873253002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1873253002/20001

[commit-bot: I haz the power, 2016-04-13 09:21:00]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-04-13 09:21:15]

Description was changed from

==========
Add a make target for generating Ctags file

This is very similar to the existing rule for a GTAGS file, and reuses
parts of it (the gtags.files file).

R=ahaas@chromium.org, mstarzinger@chromium.org, titzer@chromium.org
BUG=
==========

to

==========
Add a make target for generating Ctags file

This is very similar to the existing rule for a GTAGS file, and reuses
parts of it (the gtags.files file).

R=ahaas@chromium.org, mstarzinger@chromium.org, titzer@chromium.org
BUG=

Committed: https://crrev.com/79b1ab61c2a88fe740c94ffbb94bb5ac9ae17f40
Cr-Commit-Position: refs/heads/master@{#35435}
==========

[commit-bot: I haz the power, 2016-04-13 09:21:16]

Patchset 2 (id:??) landed as
https://crrev.com/79b1ab61c2a88fe740c94ffbb94bb5ac9ae17f40
Cr-Commit-Position: refs/heads/master@{#35435}