hotdoc: Install devhelp files at the right location

When devhelp is enabled, hotdoc generates a devhelp/ subdir that needs
to be installed to /usr/share/devhelp/. Otherwise, the html/ subdir
needs to be installed to /usr/share/doc/<project>/html/

mesonbuild/modules/hotdoc.py

@@ -339,9 +339,22 @@ class HotdocTargetBuilder:
 
         install_script = None
         if install:
+            datadir = os.path.join(self.state.get_option('prefix'), self.state.get_option('datadir'))
+            devhelp = self.kwargs.get('devhelp_activate', False)
+            if not isinstance(devhelp, bool):
+                FeatureDeprecated.single_use('hotdoc.generate_doc() devhelp_activate must be boolean', '1.1.0', self.state.subproject)
+                devhelp = False
+            if devhelp:
+                install_from = os.path.join(fullname, 'devhelp')
+                install_to = os.path.join(datadir, 'devhelp')
+            else:
+                install_from = os.path.join(fullname, 'html')
+                install_to = os.path.join(datadir, 'doc', self.name, 'html')
+
             install_script = self.state.backend.get_executable_serialisation(self.build_command + [
                 "--internal", "hotdoc",
-                "--install", os.path.join(fullname, 'html'),
+                "--install", install_from,
+                "--docdir", install_to,
                 '--name', self.name,
                 '--builddir', os.path.join(self.builddir, self.subdir)] +
                 self.hotdoc.get_command() +

mesonbuild/scripts/hotdochelper.py

@@ -15,14 +15,16 @@ parser.add_argument('--extra-extension-path', action="append", default=[])
 parser.add_argument('--name')
 parser.add_argument('--builddir')
 parser.add_argument('--project-version')
+parser.add_argument('--docdir')
 
 
 def run(argv: T.List[str]) -> int:
     options, args = parser.parse_known_args(argv)
     subenv = os.environ.copy()
 
-    for ext_path in options.extra_extension_path:
-        subenv['PYTHONPATH'] = subenv.get('PYTHONPATH', '') + ':' + ext_path
+    val = subenv.get('PYTHONPATH')
+    paths = [val] if val else []
+    subenv['PYTHONPATH'] = os.pathsep.join(paths + options.extra_extension_path)
 
     res = subprocess.call(args, cwd=options.builddir, env=subenv)
     if res != 0:
@@ -31,9 +33,7 @@ def run(argv: T.List[str]) -> int:
     if options.install:
         source_dir = os.path.join(options.builddir, options.install)
         destdir = os.environ.get('DESTDIR', '')
-        installdir = destdir_join(destdir,
-                                  os.path.join(os.environ['MESON_INSTALL_PREFIX'],
-                                               'share/doc/', options.name, "html"))
+        installdir = destdir_join(destdir, options.docdir)
 
         shutil.rmtree(installdir, ignore_errors=True)
         shutil.copytree(source_dir, installdir)