[geary: 1/2] Allow explicit setting of revision string

[Michael Gratton <mjog src gnome org>]

commit 43b52137999bf0db923c8a9a20e28d85ba17affa
Author: Daniel Kahn Gillmor <dkg fifthhorseman net>
Date:   Sun Mar 29 23:53:24 2020 -0400

    Allow explicit setting of revision string
    
    This lets a packager ensure that the binary object built from an
    unpacked source tarball is identical to the binary object created from
    a live git tree.
    
    I hope to use it in debian with something like -Drevno=debian/3.36.1-1
    during the meson configuration, so that the help dialog box and the
    bug reporting logs can identify the specific build.
    
    Signed-off-by: Daniel Kahn Gillmor <dkg fifthhorseman net>

 meson.build       | 5 ++++-
 meson_options.txt | 5 +++++
 2 files changed, 9 insertions(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 6a5bb77d..0f79826f 100644
--- a/meson.build
+++ b/meson.build
@@ -129,7 +129,10 @@ libmessagingmenu_dep = dependency('messaging-menu', version: '>= 12.10', require
 # Build variables
 geary_id = 'org.gnome.Geary@0@'.format(profile)
 geary_version = meson.project_version()
-revno = run_command('build-aux/git_version.py').stdout().strip()
+revno = get_option('revno')
+if revno == ''
+  revno = run_command('build-aux/git_version.py').stdout().strip()
+endif
 
 gnome = import('gnome')
 i18n = import('i18n')
diff --git a/meson_options.txt b/meson_options.txt
index 043f3142..5f7f7608 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -58,3 +58,8 @@ option(
   value: false,
   description: 'Whether to use explicit reference tracking.'
 )
+option(
+  'revno',
+  type: 'string',
+  description: 'Custom revision string (default extracted from "git describe")'
+)