[geary/wip/engine-header-missing-build-failure] Fix occasional "geary-engine.h: No such file or directory" build errors

[Michael Gratton <mjog src gnome org>]

commit 8d9d520c54c93842d4a279bcc477e9d54327922c
Author: Michael Gratton <mike vee net>
Date:   Thu Nov 29 09:56:25 2018 +1100

    Fix occasional "geary-engine.h: No such file or directory" build errors
    
    E.g. https://gitlab.gnome.org/GNOME/geary/-/jobs/156541
    
    On a sufficiently (non?) parallel system, targets that depend on
    geary-engine.h may get built before the geary_engine_internal_vapi
    custom target that fixes its location is executed. This splits that
    target in two (one for the publuc header fixup, one for the internal
    header/vapi) and ensures that the engine dep depends on the former.

 src/engine/meson.build | 43 ++++++++++++++++++++++++++++---------------
 1 file changed, 28 insertions(+), 15 deletions(-)
---
diff --git a/src/engine/meson.build b/src/engine/meson.build
index 222a0edc..5810a9ae 100644
--- a/src/engine/meson.build
+++ b/src/engine/meson.build
@@ -356,38 +356,53 @@ geary_engine_vala_options += [
 geary_engine_lib = static_library('geary-engine',
   geary_engine_sources,
   dependencies: geary_engine_dependencies,
-  link_with: sqlite3_unicodesn_lib,
   include_directories: config_h_dir,
   vala_args: geary_engine_vala_options,
   c_args: geary_c_options,
 )
 
-geary_engine_dep = declare_dependency(
-  link_with: [
-    geary_engine_lib,
-    sqlite3_unicodesn_lib,
+# Dummy target to fix the location of the public headers given the
+# hack above. Use capture to generate a dummy output instead of
+# specifying geary-engine.h as an output since geary_engine_lib
+# already declares that it generates that.
+geary_engine_header_fixup = custom_target(
+  'geary_engine_header_fixup',
+  output: ['geary-engine-header-fixup'],
+  capture: true,
+  command: [
+    find_program('cp'),
+    '-v',
+    'geary-engine.h',
+    '@OUTDIR@',
   ],
-  include_directories: include_directories('.'),
+  depends: geary_engine_lib
 )
 
-# Dummy target to fix the location of the public and internal headers,
-# and tell Meson about the internal VAPI
-geary_engine_internal_vapi = custom_target(
-  'geary-engine-internal-vapi',
-  input: geary_engine_sources,
+# Dummy target to fix the location of the internal headers and tell
+# Meson about the internal VAPI, given the hack above.
+geary_engine_internal_header_fixup = custom_target(
+  'geary_engine_internal_header_fixup',
   output: [
     'geary-engine-internal.h',
     'geary-engine-internal.vapi',
   ],
   command: [
     find_program('cp'),
-    'geary-engine.h',
     'geary-engine-internal.h',
     '@OUTDIR@',
   ],
   depends: geary_engine_lib
 )
 
+geary_engine_dep = declare_dependency(
+  link_with: [
+    geary_engine_lib,
+    sqlite3_unicodesn_lib
+  ],
+  include_directories: include_directories('.'),
+  sources: geary_engine_header_fixup
+)
+
 geary_engine_internal_dep = declare_dependency(
   # Can't just include geary_engine_lib in link_with since that will
   # pull in the public header and we get duplicate symbol errors.
@@ -399,7 +414,5 @@ geary_engine_internal_dep = declare_dependency(
     sqlite3_unicodesn_lib,
   ],
   include_directories: include_directories('.'),
-  sources: [
-    geary_engine_internal_vapi
-  ],
+  sources: geary_engine_internal_header_fixup
 )