build: Set the module path in the build

Instead of trying to find the module by traversing from the executable,
have meson hardcode the path. I *think* this is a little less fragile.

blueprint-compiler.py

@@ -21,18 +21,19 @@
 
 import os, sys
 
-# Try to find the python module, assuming the current file is installed to (prefix)/bin
-dirname = os.path.join(os.path.dirname(os.path.dirname(__file__)), "share", "blueprint-compiler")
-if os.path.isdir(os.path.join(dirname, "blueprintcompiler")):
-    sys.path.insert(0, dirname)
-
-# Get the configured (or, if running from source, not configured) version number
+# These variables should be set by meson. If they aren't, we're running
+# uninstalled, and we might have to guess some values.
 version = "@VERSION@"
+module_path = "@MODULE_PATH@"
+libdir = "@LIBDIR@"
 
-def literal(key):
-    return "@" + key + "@"
+if version == "\u0040VERSION@":
+    version = "uninstalled"
+else:
+    # If Meson set the configuration values, insert the module path it set
+    sys.path.insert(0, module_path)
 
 from blueprintcompiler import main
 
 if __name__ == "__main__":
-    main.main("uninstalled" if version == literal("VERSION") else version)
+    main.main(version)

meson.build

@@ -17,22 +17,29 @@ configure_file(
   install_dir: join_paths(datadir, 'pkgconfig'),
 )
 
+config = configuration_data({
+  'VERSION': meson.project_version(),
+  'LIBDIR': get_option('prefix') / get_option('libdir'),
+})
+
+if meson.is_subproject()
+  config.set('MODULE_PATH', meson.current_source_dir())
+else
+  config.set('MODULE_PATH', py.get_install_dir())
+endif
+
 blueprint_compiler = configure_file(
   input: 'blueprint-compiler.py',
   output: 'blueprint-compiler',
-  configuration: {
-    'VERSION': meson.project_version(),
-  },
+  configuration: config,
   install: not meson.is_subproject(),
   install_dir: get_option('bindir'),
 )
 
-# Don't use the output configure_file here--that file is in the build directory
-# and won't be able to find the python modules in the source directory.
-meson.override_find_program('blueprint-compiler', find_program('blueprint-compiler.py'))
-
-if not meson.is_subproject()
-  install_subdir('blueprintcompiler', install_dir: datadir / 'blueprint-compiler')
+if meson.is_subproject()
+  meson.override_find_program('blueprint-compiler', blueprint_compiler)
+else
+  install_subdir('blueprintcompiler', install_dir: py.get_install_dir())
 endif
 
 subdir('tests')