html-preview: run sphinx-build command manually

Using the library to perform this work is not working correctly, so at
least for now (and the 3.34 release) we should just call the commands
directly using a subprocess launcher.

src/plugins/html-preview/html_preview.py

@@ -482,28 +482,31 @@ class HtmlPreviewPage(Ide.Page):
     def get_sphinx_rst_worker(self, task, text, path, basedir, builddir):
         add_override_file(path, text)
 
+        if GLib.find_program_in_path('sphinx-build-3'):
+            program = 'sphinx-build-3'
+        else:
+            program = 'sphinx-build'
+
         rel_path = os.path.relpath(path, start=basedir)
-        command = ['sphinx-build', '-Q', '-b', 'html', basedir, builddir, path]
+        command = [program, '-Q', '-b', 'html', basedir, builddir, path]
 
         rel_path_html = os.path.splitext(rel_path)[0] + '.html'
         builddir_path = os.path.join(builddir, rel_path_html)
 
         try:
-            import sphinx.cmd.build
-            build_main = sphinx.cmd.build.main
-        except:
-            build_main = sphinx.build_main
-
-        result = not build_main(command)
-        remove_override_file(path)
-
-        if not result:
-            task.builddir_path = None
-            task.return_error(GLib.Error('\'sphinx-build\' command error for {}'.format(path)))
-            return
+            launcher = Ide.SubprocessLauncher.new(0) # Gio.SubprocessFlags.STDOUT_SILENCE |
+                                                     # Gio.SubprocessFlags.STDERR_SILENCE)
+            launcher.push_args(command)
+            subprocess = launcher.spawn()
+            subprocess.wait_check()
+
+            task.builddir_path = builddir_path
+            task.return_boolean(True)
+        except Exception as ex:
+            task.return_error(GLib.Error(ex))
+        finally:
+            remove_override_file(path)
 
-        task.builddir_path = builddir_path
-        task.return_boolean(True)
 
     def get_sphinx_rst_finish(self, result):
         succes = result.propagate_boolean()