[pango/improve-fontconfig-dep-search] build: Only use fallback dep for FontConfig when needed/requested

[Chun-wei Fan <fanchunwei src gnome org>]

commit da059347f8df5fc180b4538d9d3c50867c401fbd
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Fri Jul 19 18:47:13 2019 +0800

    build: Only use fallback dep for FontConfig when needed/requested
    
    Windows and macOS only optionally requires FontConfig, so:
    
    -Add an option, for Windows and macOS, whether we want to use FontConfig
     on these platforms.  This is ignored on *NIX, where FontConfig will
     always be used.
    
    -We still look for FontConfig first via pkg-config files, and on MSVC
     builds, via looking for its headers and .lib files.  If FontConfig is
     required (or requested) but is not found, we then use the fallback
     dependency for it.

 meson.build       | 11 +++++++++--
 meson_options.txt |  4 ++++
 2 files changed, 13 insertions(+), 2 deletions(-)
---
diff --git a/meson.build b/meson.build
index 13d9bbff..694c0a19 100644
--- a/meson.build
+++ b/meson.build
@@ -259,8 +259,10 @@ if harfbuzz_dep.found()
   pango_deps += harfbuzz_dep
 endif
 
-fontconfig_dep = dependency('fontconfig', version: fontconfig_req_version, required: false,
-                            fallback: ['fontconfig', 'fontconfig_dep'])
+# Only use FontConfig fallback when required or requested
+fontconfig_required = (host_system != 'windows' and host_system != 'darwin') or get_option('use_fontconfig')
+
+fontconfig_dep = dependency('fontconfig', version: fontconfig_req_version, required: false)
 if fontconfig_dep.found()
   fontconfig_pc = 'fontconfig'
 else
@@ -274,6 +276,11 @@ else
   endif
 endif
 
+if fontconfig_required and not fontconfig_dep.found()
+  fontconfig_dep = dependency('fontconfig', version: fontconfig_req_version,
+                              fallback: ['fontconfig', 'fontconfig_dep'])
+endif
+
 if fontconfig_dep.found()
   pango_deps += fontconfig_dep
 
diff --git a/meson_options.txt b/meson_options.txt
index d2f5f302..7a59fa2b 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -10,3 +10,7 @@ option('install-tests',
        description : 'Install tests',
        type: 'boolean',
        value: 'false')
+option('use_fontconfig',
+       description : 'Force using FontConfig where it is optional, on Windows and macOS.  This is ignored on 
platforms where it is required',
+       type: 'boolean',
+       value: 'false')