[Mesa-dev] [PATCH mesa] meson: bring MESA_GIT_SHA1 in line with other build systems

[Eric Engestrom]

Meson's vcs_tag() uses the output of `git describe`, eg.
  17.3-branchpoint-5-gfbf29c3cd15ae831e249+

Whereas the other build systems used a script that outputs only the sha1
of the HEAD commit, eg.
  fbf29c3cd1

Given that this information is used by printing it next to the version
number, there's some redundancy here, and inconsistency between build
systems.

Bring Meson in line by making it use the same script, with the added
advantage of now supporting the MESA_GIT_SHA1_OVERRIDE env var.

Downside is, files using MESA_GIT_SHA1 now have to be rebuilt every
time.

Signed-off-by: Eric Engestrom <eric at engestrom.ch>
---
I don't like this solution because of the downside mentioned; I'm not
sure the redundant information is really an issue, and the inconsistency
aspect will go away once Meson becomes The One True Build System, and
the env var fallback can be implemented with a meson option instead,
although I don't like that because if you set the git version once, it
will be carried over across git pulls, but if we make it clear that such
an option is only to be used by build scripts it should be fine.

I'm leaning towards "let's accept `git describe` as the new information
printed with the version", and implement the meson option fallback.
Thoughts?
---
 bin/meson.build | 21 +++++++++++++++++++++
 meson.build     |  1 +
 src/meson.build |  6 +++++-
 3 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 bin/meson.build

diff --git a/bin/meson.build b/bin/meson.build
new file mode 100644
index 0000000000..b8b44baf7d
--- /dev/null
+++ b/bin/meson.build
@@ -0,0 +1,21 @@
+# Copyright © 2017 Eric Engestrom
+
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+git_sha1_gen_py = files('git_sha1_gen.py')
diff --git a/meson.build b/meson.build
index 09e4615a14..8a92ddc9a9 100644
--- a/meson.build
+++ b/meson.build
@@ -834,4 +834,5 @@ endif
 pkg = import('pkgconfig')
 
 subdir('include')
+subdir('bin')
 subdir('src')
diff --git a/src/meson.build b/src/meson.build
index 9b1b0ae594..b35295e9d3 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -34,9 +34,13 @@ libglsl_util = static_library(
   build_by_default : false,
 )
 
-sha1_h = vcs_tag(
+sha1_h = custom_target(
+  'git_sha1.h',
   input : 'git_sha1.h.in',
   output : 'git_sha1.h',
+  command : [prog_python2, git_sha1_gen_py],
+  capture : true,
+  build_always : true,
 )
 
 subdir('gtest')
-- 
Cheers,
  Eric