[babl] Another project can add babl as a subproject

[Øyvind "pippin" Kolås <ok src gnome org>]

commit fbf3dd9301dbe8afbfca915051cb936f7c2bd59a
Author: santouits <santouits users noreply github com>
Date:   Sun Sep 6 15:16:52 2020 +0300

    Another project can add babl as a subproject

 .gitignore                        |  2 ++
 babl/meson.build                  | 21 +++++++++++++++------
 docs/build_as_meson_subproject.md | 23 +++++++++++++++++++++++
 docs/meson.build                  |  8 ++++----
 extensions/meson.build            |  2 +-
 meson.build                       | 13 +++++++++++--
 6 files changed, 56 insertions(+), 13 deletions(-)
---
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 000000000..a3523b715
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+# Meson
+_build
diff --git a/babl/meson.build b/babl/meson.build
index fed8fe91b..623367804 100644
--- a/babl/meson.build
+++ b/babl/meson.build
@@ -13,10 +13,10 @@ babl_c_args = [
 
 # symbol maps
 version_script = custom_target('babl.map',
-  input : meson.source_root() / 'export-symbols',
+  input : export_symbols_file,
   output: ['babl.map', 'babl.map.clang'],
   command: [
-  find_program(meson.source_root() / 'gen_babl_map.py'),
+  find_program(gen_babl_map_file),
   '@INPUT@',
   '@OUTPUT0@',
   ],
@@ -76,7 +76,7 @@ if git_bin.found() and run_command(
     command: [ git_bin.path(), 'describe', '--always' ],
   )
 
-  if env_bin.found()
+  if env_bin.found() and not meson.is_subproject()
     meson.add_dist_script(
       [ 'ninja', 'babl/git-version.h', ],
     )
@@ -139,19 +139,28 @@ install_headers(babl_headers,
   subdir: join_paths(lib_name, 'babl')
 )
 
+babl_deps = [math, thread, dl, lcms]
+babl_includes = [rootInclude, bablBaseInclude]
+
 babl = library(
   lib_name,
   babl_sources,
-  include_directories: [rootInclude, bablBaseInclude],
+  include_directories: babl_includes,
   c_args: babl_c_args,
   link_whole: babl_base,
   link_args: babl_link_args,
-  dependencies: [math, thread, dl, lcms],
+  dependencies: babl_deps,
   link_depends: version_script,
   version: so_version,
   install: true,
 )
 
+libbabl_dep = declare_dependency(
+  include_directories: babl_includes,
+  link_with: babl,
+  dependencies: babl_deps
+)
+
 if build_gir
   # identity filter, so GIR doesn't choke on the Babl type
   # (since it has the same name as the Babl namespace)
@@ -169,7 +178,7 @@ if build_gir
   )
 
   if build_vapi
-    gnome.generate_vapi(lib_name,
+    babl_vapi = gnome.generate_vapi(lib_name,
       sources: babl_gir[0],
       install: true,
     )
diff --git a/docs/build_as_meson_subproject.md b/docs/build_as_meson_subproject.md
new file mode 100644
index 000000000..d6e1c6556
--- /dev/null
+++ b/docs/build_as_meson_subproject.md
@@ -0,0 +1,23 @@
+
+Including babl as a meson subproject in your project:
+
+You create a babl.wrap file inside a folder named 'subprojects'
+which contains a way to download the babl source.
+See https://mesonbuild.com/Wrap-dependency-system-manual.html.
+An example will be:
+```
+[wrap-git]
+url = https://gitlab.gnome.org/GNOME/babl
+revision = master
+depth = 1
+```
+
+Next, include in your meson.build file something like this:
+```
+babl = dependency('babl', fallback: ['babl', 'libbabl_dep'])
+```
+
+If babl is installed in your system, meson will use that one,
+otherwise it will download and build babl.
+
+
diff --git a/docs/meson.build b/docs/meson.build
index eefeb915c..1aa52ed42 100644
--- a/docs/meson.build
+++ b/docs/meson.build
@@ -6,7 +6,7 @@ scptarget = host + ':' + location + '/'
 
 
 xml_insert = find_program(
-  meson.source_root() / 'tools' / 'xml-insert.py',
+  xml_insert_file,
   native: true
 )
 
@@ -46,9 +46,9 @@ endif
 TOC = files('toc')
 html_files = {
   'index': [index_static_html, [
-    ['AUTHORS', files(meson.source_root() / 'AUTHORS')],
-    ['TODO',    files(meson.source_root() / 'TODO')],
-    ['NEWS',    files(meson.source_root() / 'NEWS')],
+    ['AUTHORS', authors_file],
+    ['TODO',    todo_file],
+    ['NEWS',    news_file],
     ['TOC',     TOC],
   ]],
   'Reference': ['auto', [
diff --git a/extensions/meson.build b/extensions/meson.build
index 850793f75..598857c0d 100644
--- a/extensions/meson.build
+++ b/extensions/meson.build
@@ -54,7 +54,7 @@ extensions = [
 ]
 
 foreach ext : extensions
-  library(
+  shared_library(
     ext[0],
     ext[0] + '.c',
     c_args: ext[1],
diff --git a/meson.build b/meson.build
index f6089a33d..1362b6acf 100644
--- a/meson.build
+++ b/meson.build
@@ -415,6 +415,15 @@ configure_file(
   configuration: conf
 )
 
+################################################################################
+# Global variables
+
+xml_insert_file = files('tools' / 'xml-insert.py')
+authors_file = files('AUTHORS')
+news_file = files('NEWS')
+todo_file = files('TODO')
+export_symbols_file = files('export-symbols')
+gen_babl_map_file = files('gen_babl_map.py')
 
 ################################################################################
 # Subdirs
@@ -447,11 +456,11 @@ endif
 
 
 # pkg-config file
-pkgconfig.generate(filebase: 'babl',
+pkgconfig.generate(babl,
+  filebase: 'babl',
   name: 'babl',
   description: 'Pixel encoding and color space conversion engine.',
   version: meson.project_version(),
-  libraries: [ babl ],
   libraries_private: [
     '-lm',
   ],