tree-sitter/update: prepare moving more stuff to python

I don’t want to split up the python code, so for now I’m just passing
a “mode” to the script to run a different subset of the functionality.

pkgs/development/tools/parsing/tree-sitter/update.nix

@@ -407,8 +407,8 @@ let
   # TODO
   urlEscape = x: x;
 
-  # update one tree-sitter grammar repo and print their nix-prefetch-git output
-  updateGrammar = writers.writePython3 "latest-github-release" {
+  # implementation of the fetching of repo information from github
+  fetchImpl = writers.writePython3 "fetchImpl" {
     flakeIgnore = ["E501"];
   } ''
     from urllib.parse import quote
@@ -419,7 +419,8 @@ let
 
     debug = True if os.environ.get("DEBUG", False) else False
 
-    jsonArg = sys.argv[1]
+    mode = sys.argv[1]
+    jsonArg = json.loads(sys.argv[2])
 
 
     def curl_args(orga, repo, token):
@@ -458,7 +459,9 @@ let
         yield version_rev
 
 
-    match json.loads(jsonArg):
+    def fetchRepo():
+        """fetch the given repo and print its nix-prefetch output to stdout"""
+        match jsonArg:
             case {"orga": orga, "repo": repo}:
                 token = os.environ.get("GITHUB_TOKEN", None)
                 curl_cmd = list(curl_args(orga, repo, token))
@@ -481,6 +484,13 @@ let
                 )
             case _:
                 sys.exit("input json must have `orga` and `repo` keys")
+
+
+    match mode:
+        case "fetch-repo":
+            fetchRepo()
+        case _:
+            sys.exit(f"mode {mode} unknown")
   '';
 
   # find the latest repos of a github organization
@@ -522,7 +532,7 @@ let
     mkdir -p "$outputDir"
     ${foreachSh allGrammars
       ({name, orga, repo}: ''
-        ${updateGrammar} '${lib.generators.toJSON {} {inherit orga repo;}}' \
+        ${fetchImpl} fetch-repo '${lib.generators.toJSON {} {inherit orga repo;}}' \
           > $outputDir/${name}.json
       '')}
     ( echo "{ lib }:"