meson: Add files in manifest as respack.py input

This makes meson detect changes to files like default_config.json
and rebuild libresrc.cpp when necessary.

meson.build

@@ -1,6 +1,6 @@
 project('Aegisub', ['c', 'cpp'],
         license: 'BSD-3-Clause',
-        meson_version: '>=0.56.1',
+        meson_version: '>=0.57.0',
         default_options: ['cpp_std=c++14', 'buildtype=debugoptimized'],
         version: '3.2.2')
 

src/libresrc/meson.build

@@ -1,3 +1,5 @@
+fs = import('fs')
+
 respack = find_program(meson.project_source_root() / 'tools/respack.py')
 
 resrc = [
@@ -12,17 +14,25 @@ conf_platform_json = configure_file(input: 'default_config_platform.json.in',
                                     configuration: conf_platform)
 
 if host_machine.system() == 'darwin'
-    resrc += custom_target('default_config.{cpp,h}',
-                           command: [respack, '@INPUT0@', '@OUTPUT@'],
-                           input: [files('manifest_osx.respack'), conf_platform_json],
-                           output: ['default_config.cpp', 'default_config.h'])
+    resmanifest = 'manifest_osx.respack'
 else
-    resrc += custom_target('default_config.{cpp,h}',
-                           command: [respack, '@INPUT0@', '@OUTPUT@'],
-                           input: [files('manifest.respack'), conf_platform_json],
-                           output: ['default_config.cpp', 'default_config.h'])
+    resmanifest = 'manifest.respack'
 endif
 
+resmanifest_files = [conf_platform_json]
+# Filter out the files we've generated ourselves
+foreach rfile : fs.read(resmanifest).strip().split('\n')
+    rfile_s = rfile.strip()
+    if fs.is_file(rfile_s)
+        resmanifest_files += files(rfile_s)
+    endif
+endforeach
+
+resrc += custom_target('default_config.{cpp,h}',
+                        command: [respack, '@INPUT0@', '@OUTPUT@'],
+                        input: [files(resmanifest), resmanifest_files],
+                        output: ['default_config.cpp', 'default_config.h'])
+
 
 libresrc_inc = include_directories('.')
 libresrc = static_library('resrc', 'libresrc.cpp', resrc, include_directories: deps_inc, dependencies: deps)