Allow using several custom template directories (#10587)

Allow using several directories in read_templates.

7 files changed, 98 insertions, 27 deletions

diff --git a/changelog.d/10587.misc b/changelog.d/10587.misc
new file mode 100644
index 0000000000..4c6167977c
--- /dev/null
+++ b/changelog.d/10587.misc
@@ -0,0 +1 @@
+Allow multiple custom directories in `read_templates`.
diff --git a/synapse/config/_base.py b/synapse/config/_base.py
index d6ec618f8f..2cc242782a 100644
--- a/synapse/config/_base.py
+++ b/synapse/config/_base.py
@@ -237,13 +237,14 @@ class Config:
     def read_templates(
         self,
         filenames: List[str],
-        custom_template_directory: Optional[str] = None,
+        custom_template_directories: Optional[Iterable[str]] = None,
     ) -> List[jinja2.Template]:
         """Load a list of template files from disk using the given variables.
 
         This function will attempt to load the given templates from the default Synapse
-        template directory. If `custom_template_directory` is supplied, that directory
-        is tried first.
+        template directory. If `custom_template_directories` is supplied, any directory
+        in this list is tried (in the order they appear in the list) before trying
+        Synapse's default directory.
 
         Files read are treated as Jinja templates. The templates are not rendered yet
         and have autoescape enabled.
@@ -251,8 +252,8 @@ class Config:
         Args:
             filenames: A list of template filenames to read.
 
-            custom_template_directory: A directory to try to look for the templates
-                before using the default Synapse template directory instead.
+            custom_template_directories: A list of directory to try to look for the
+                templates before using the default Synapse template directory instead.
 
         Raises:
             ConfigError: if the file's path is incorrect or otherwise cannot be read.
@@ -260,20 +261,26 @@ class Config:
         Returns:
             A list of jinja2 templates.
         """
-        search_directories = [self.default_template_dir]
-
-        # The loader will first look in the custom template directory (if specified) for the
-        # given filename. If it doesn't find it, it will use the default template dir instead
-        if custom_template_directory:
-            # Check that the given template directory exists
-            if not self.path_exists(custom_template_directory):
-                raise ConfigError(
-                    "Configured template directory does not exist: %s"
-                    % (custom_template_directory,)
-                )
+        search_directories = []
+
+        # The loader will first look in the custom template directories (if specified)
+        # for the given filename. If it doesn't find it, it will use the default
+        # template dir instead.
+        if custom_template_directories is not None:
+            for custom_template_directory in custom_template_directories:
+                # Check that the given template directory exists
+                if not self.path_exists(custom_template_directory):
+                    raise ConfigError(
+                        "Configured template directory does not exist: %s"
+                        % (custom_template_directory,)
+                    )
+
+                # Search the custom template directory as well
+                search_directories.append(custom_template_directory)
 
-            # Search the custom template directory as well
-            search_directories.insert(0, custom_template_directory)
+        # Append the default directory at the end of the list so Jinja can fallback on it
+        # if a template is missing from any custom directory.
+        search_directories.append(self.default_template_dir)
 
         # TODO: switch to synapse.util.templates.build_jinja_env
         loader = jinja2.FileSystemLoader(search_directories)
diff --git a/synapse/config/account_validity.py b/synapse/config/account_validity.py
index 6be4eafe55..9acce5996e 100644
--- a/synapse/config/account_validity.py
+++ b/synapse/config/account_validity.py
@@ -88,5 +88,5 @@ class AccountValidityConfig(Config):
                 "account_previously_renewed.html",
                 invalid_token_template_filename,
             ],
-            account_validity_template_dir,
+            (td for td in (account_validity_template_dir,) if td),
         )
diff --git a/synapse/config/emailconfig.py b/synapse/config/emailconfig.py
index 42526502f0..fc74b4a8b9 100644
--- a/synapse/config/emailconfig.py
+++ b/synapse/config/emailconfig.py
@@ -257,7 +257,9 @@ class EmailConfig(Config):
                     registration_template_success_html,
                     add_threepid_template_success_html,
                 ],
-                template_dir,
+                (
+                    td for td in (template_dir,) if td
+                ),  # Filter out template_dir if not provided
             )
 
             # Render templates that do not contain any placeholders
@@ -297,7 +299,7 @@ class EmailConfig(Config):
                 self.email_notif_template_text,
             ) = self.read_templates(
                 [notif_template_html, notif_template_text],
-                template_dir,
+                (td for td in (template_dir,) if td),
             )
 
             self.email_notif_for_new_users = email_config.get(
@@ -320,7 +322,7 @@ class EmailConfig(Config):
                 self.account_validity_template_text,
             ) = self.read_templates(
                 [expiry_template_html, expiry_template_text],
-                template_dir,
+                (td for td in (template_dir,) if td),
             )
 
         subjects_config = email_config.get("subjects", {})
diff --git a/synapse/config/sso.py b/synapse/config/sso.py
index d0f04cf8e6..4b590e0535 100644
--- a/synapse/config/sso.py
+++ b/synapse/config/sso.py
@@ -63,7 +63,7 @@ class SSOConfig(Config):
                 "sso_auth_success.html",
                 "sso_auth_bad_user.html",
             ],
-            self.sso_template_dir,
+            (td for td in (self.sso_template_dir,) if td),
         )
 
         # These templates have no placeholders, so render them here
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index 1cc13fc97b..82725853bc 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -677,7 +677,10 @@ class ModuleApi:
             A list containing the loaded templates, with the orders matching the one of
             the filenames parameter.
         """
-        return self._hs.config.read_templates(filenames, custom_template_directory)
+        return self._hs.config.read_templates(
+            filenames,
+            (td for td in (custom_template_directory,) if td),
+        )
 
 
 class PublicRoomListManager:
diff --git a/tests/config/test_base.py b/tests/config/test_base.py
index 84ae3b88ae..baa5313fb3 100644
--- a/tests/config/test_base.py
+++ b/tests/config/test_base.py
@@ -30,7 +30,7 @@ class BaseConfigTestCase(unittest.HomeserverTestCase):
         # contain template files
         with tempfile.TemporaryDirectory() as tmp_dir:
             # Attempt to load an HTML template from our custom template directory
-            template = self.hs.config.read_templates(["sso_error.html"], tmp_dir)[0]
+            template = self.hs.config.read_templates(["sso_error.html"], (tmp_dir,))[0]
 
         # If no errors, we should've gotten the default template instead
 
@@ -60,7 +60,7 @@ class BaseConfigTestCase(unittest.HomeserverTestCase):
 
                 # Attempt to load the template from our custom template directory
                 template = (
-                    self.hs.config.read_templates([template_filename], tmp_dir)
+                    self.hs.config.read_templates([template_filename], (tmp_dir,))
                 )[0]
 
         # Render the template
@@ -74,8 +74,66 @@ class BaseConfigTestCase(unittest.HomeserverTestCase):
             "Template file did not contain our test string",
         )
 
+    def test_multiple_custom_template_directories(self):
+        """Tests that directories are searched in the right order if multiple custom
+        template directories are provided.
+        """
+        # Create two temporary directories on the filesystem.
+        tempdirs = [
+            tempfile.TemporaryDirectory(),
+            tempfile.TemporaryDirectory(),
+        ]
+
+        # Create one template in each directory, whose content is the index of the
+        # directory in the list.
+        template_filename = "my_template.html.j2"
+        for i in range(len(tempdirs)):
+            tempdir = tempdirs[i]
+            template_path = os.path.join(tempdir.name, template_filename)
+
+            with open(template_path, "w") as fp:
+                fp.write(str(i))
+                fp.flush()
+
+        # Retrieve the template.
+        template = (
+            self.hs.config.read_templates(
+                [template_filename],
+                (td.name for td in tempdirs),
+            )
+        )[0]
+
+        # Test that we got the template we dropped in the first directory in the list.
+        self.assertEqual(template.render(), "0")
+
+        # Add another template, this one only in the second directory in the list, so we
+        # can test that the second directory is still searched into when no matching file
+        # could be found in the first one.
+        other_template_name = "my_other_template.html.j2"
+        other_template_path = os.path.join(tempdirs[1].name, other_template_name)
+
+        with open(other_template_path, "w") as fp:
+            fp.write("hello world")
+            fp.flush()
+
+        # Retrieve the template.
+        template = (
+            self.hs.config.read_templates(
+                [other_template_name],
+                (td.name for td in tempdirs),
+            )
+        )[0]
+
+        # Test that the file has the expected content.
+        self.assertEqual(template.render(), "hello world")
+
+        # Cleanup the temporary directories manually since we're not using a context
+        # manager.
+        for td in tempdirs:
+            td.cleanup()
+
     def test_loading_template_from_nonexistent_custom_directory(self):
         with self.assertRaises(ConfigError):
             self.hs.config.read_templates(
-                ["some_filename.html"], "a_nonexistent_directory"
+                ["some_filename.html"], ("a_nonexistent_directory",)
             )