nixpkgs-plugin-update: generate sri hashes (#471237)

pkgs/development/python-modules/nixpkgs-plugin-update/nixpkgs-plugin-update/src/nixpkgs_plugin_update/__init__.py

@@ -201,7 +201,7 @@ class Repo:
         return f"""fetchgit {{
       url = "{self.uri}";
       rev = "{plugin.commit}";
-      sha256 = "{plugin.sha256}";
+      hash = "{plugin.to_sri_hash()}";
     }}"""
 
 
@@ -428,7 +428,7 @@ class RepoGitHub(Repo):
       owner = "{self.owner}";
       repo = "{self.repo}";
       rev = "{plugin.commit}";
-      sha256 = "{plugin.sha256}";{submodule_attr}
+      hash = "{plugin.to_sri_hash()}";{submodule_attr}
     }}"""
 
 
@@ -483,6 +483,23 @@ class Plugin:
     def normalized_name(self) -> str:
         return self.name.replace(".", "-")
 
+    def to_sri_hash(self) -> str:
+        if self.sha256.startswith("sha256-"):
+            return self.sha256
+
+        cmd = [
+            "nix",
+            "hash",
+            "convert",
+            "--hash-algo",
+            "sha256",
+            "--to",
+            "sri",
+            self.sha256,
+        ]
+        result = subprocess.check_output(cmd, stderr=subprocess.DEVNULL)
+        return result.decode("utf-8").strip()
+
     @property
     def version(self) -> str:
         assert self.date is not None