[geary: 1/3] Allow to opt-out from using libunwind.

[Michael Gratton <mjog src gnome org>]

commit a1377f345198c454001985a18e71306ba28c0a35
Author: Thomas Moschny <thomas moschny gmx de>
Date:   Sun Feb 17 17:56:46 2019 +0100

    Allow to opt-out from using libunwind.

 meson.build                             | 33 +++++++++++++++++----------------
 meson_options.txt                       |  1 +
 src/engine/meson.build                  | 11 ++++++++++-
 src/engine/util/util-error-context.vala |  4 ++++
 4 files changed, 32 insertions(+), 17 deletions(-)
---
diff --git a/meson.build b/meson.build
index 290faca5..f0574eeb 100644
--- a/meson.build
+++ b/meson.build
@@ -1,7 +1,7 @@
 project('geary', [ 'vala', 'c' ],
   version: '3.32-dev',
   license: 'LGPL2.1+',
-  meson_version: '>= 0.43',
+  meson_version: '>= 0.47',
 )
 
 gnome = import('gnome')
@@ -70,8 +70,8 @@ libmath = cc.find_library('m')
 libnotify = dependency('libnotify', version: '>= 0.7.5')
 libsecret = dependency('libsecret-1', version: '>= 0.11')
 libsoup = dependency('libsoup-2.4', version: '>= 2.48')
-libunwind_dep = dependency('libunwind', version: '>= 1.1')
-libunwind_generic_dep = dependency('libunwind-generic', version: '>= 1.1')
+libunwind_dep = dependency('libunwind', version: '>= 1.1', required: get_option('libunwind'))
+libunwind_generic_dep = dependency('libunwind-generic', version: '>= 1.1', required: get_option('libunwind'))
 libxml = dependency('libxml-2.0', version: '>= 2.7.8')
 posix = valac.find_library('posix')
 webkit2gtk_web_extension = dependency('webkit2gtk-web-extension-4.0', version: '>=' + target_webkit)
@@ -81,19 +81,20 @@ if not enchant.found()
   enchant = dependency('enchant', version: '>=1.6')
 endif
 
-
-# Libunwind system dependencies above ensures appropriate versions,
-# but this declared depencency is what we actually build against so we
-# can include the custom VAPI correctly. We need to add unwind_lib to
-# the search path for these so Flatpak builds can find the C lib.
-unwind_lib = libunwind_dep.get_pkgconfig_variable('libdir')
-libunwind = declare_dependency(
-   dependencies: [
-     valac.find_library('libunwind', dirs: [vapi_dir, unwind_lib]),
-     cc.find_library('libunwind', dirs: unwind_lib),
-     cc.find_library('libunwind-generic', dirs: unwind_lib)
-   ],
- )
+if libunwind_dep.found()
+  # Libunwind system dependencies above ensures appropriate versions,
+  # but this declared depencency is what we actually build against so we
+  # can include the custom VAPI correctly. We need to add unwind_lib to
+  # the search path for these so Flatpak builds can find the C lib.
+  unwind_lib = libunwind_dep.get_pkgconfig_variable('libdir')
+  libunwind = declare_dependency(
+     dependencies: [
+       valac.find_library('libunwind', dirs: [vapi_dir, unwind_lib]),
+       cc.find_library('libunwind', dirs: unwind_lib),
+       cc.find_library('libunwind-generic', dirs: unwind_lib)
+     ],
+   )
+endif
 
 # Optional libraries
 libunity = dependency('unity', version: '>= 5.12.0', required: false)
diff --git a/meson_options.txt b/meson_options.txt
index 234e979d..f29b0f0c 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -4,3 +4,4 @@ option('poodle', type: 'boolean', value: true, description: 'Whether to apply th
 option('ref_tracking', type: 'boolean', value: false, description: 'Whether to use explicit reference 
tracking.')
 option('iso_639_xml', type: 'string', value: '', description: 'Full path to the ISO 639 XML file.')
 option('iso_3166_xml', type: 'string', value: '', description: 'Full path to the ISO 3166 XML file.')
+option('libunwind', type: 'feature', value: 'enabled', description: 'Whether to use libunwind.')
diff --git a/src/engine/meson.build b/src/engine/meson.build
index f9fb1626..3f5bfad9 100644
--- a/src/engine/meson.build
+++ b/src/engine/meson.build
@@ -332,12 +332,15 @@ geary_engine_dependencies = [
   glib,
   gmime,
   javascriptcoregtk,
-  libunwind,
   libxml,
   posix,
   sqlite
 ]
 
+if libunwind_dep.found()
+  geary_engine_dependencies += libunwind
+endif
+
 build_dir = meson.current_build_dir()
 
 # Generate internal VAPI for unit testing. See Meson issue
@@ -349,6 +352,12 @@ geary_engine_vala_options += [
   '--internal-vapi=@0@/geary-engine-internal.vapi'.format(build_dir)
 ]
 
+if libunwind_dep.found()
+  geary_engine_vala_options += [
+    '-D', 'HAVE_LIBUNWIND',
+  ]
+endif
+
 geary_engine_lib = static_library('geary-engine',
   geary_engine_sources,
   dependencies: geary_engine_dependencies,
diff --git a/src/engine/util/util-error-context.vala b/src/engine/util/util-error-context.vala
index 81cfcb8b..b4f3008f 100644
--- a/src/engine/util/util-error-context.vala
+++ b/src/engine/util/util-error-context.vala
@@ -28,6 +28,7 @@ public class Geary.ErrorContext : BaseObject {
         public string name = "unknown";
 
 
+#if HAVE_LIBUNWIND
         internal StackFrame(Unwind.Cursor frame) {
             uint8 proc_name[256];
             int ret = -frame.get_proc_name(proc_name);
@@ -36,6 +37,7 @@ public class Geary.ErrorContext : BaseObject {
                 this.name = (string) proc_name;
             }
         }
+#endif
 
         public string to_string() {
             return this.name;
@@ -56,6 +58,7 @@ public class Geary.ErrorContext : BaseObject {
     public ErrorContext(GLib.Error thrown) {
         this.thrown = thrown;
 
+#if HAVE_LIBUNWIND
         Unwind.Context trace = Unwind.Context();
         Unwind.Cursor cursor = Unwind.Cursor.local(trace);
 
@@ -64,6 +67,7 @@ public class Geary.ErrorContext : BaseObject {
         while (cursor.step() != 0) {
             this.backtrace.add(new StackFrame(cursor));
         }
+#endif
     }
 
     /** Returns a string representation of the error type, for debugging. */