qgis-plugins: improve nix hash creation during update

pkgs/qgis/plugins.nix

@@ -13,7 +13,7 @@ stdenv.mkDerivation {
 
   src = fetchurl {
     url = plugin.url;
-    sha256 = plugin.hash;
+    hash = plugin.hash;
   };
 
   dontUnpack = true;

pkgs/qgis/update-plugins.py

@@ -8,17 +8,39 @@
 
 MIN_DOWNLOADS = 100000
 
-qgis_plugins_xml = sys.argv[1]
+plugins_xml = sys.argv[1]
 
+if plugins_xml == "qgis-plugins.xml":
+    qgis_package = "qgis"
+elif plugins_xml == "qgis-ltr-plugins.xml":
+    qgis_package = "qgis-ltr"
 
-def get_nix_hash(url):
+
+def get_nix_hash(qgis_package, name, version):
     cmd = run(
-        ["nix", "store", "prefetch-file",
-            "--option", "download-attempts", "10",
-            "--json", url
-        ], capture_output=True, text=True
+        ["nix", "eval", "--raw", ".#{}-plugin-{}.version".format(qgis_package, name)],
+        capture_output=True,
+        text=True,
     )
-    return json.loads(cmd.stdout)["hash"]
+
+    # if plugin already exists in the same version
+    if cmd.stdout == version:
+        cmd = run(
+            ["nix", "eval", "--raw", ".#qgis-plugin-{}.src.outputHash".format(name)],
+            capture_output=True,
+            text=True,
+        )
+        return cmd.stdout
+
+    # if plugin doesn't exist or the version is different
+    else:
+        cmd = run(
+            ["nix", "store", "prefetch-file",
+                "--option", "download-attempts", "10",
+                "--json", url
+            ], capture_output=True, text=True
+        )
+        return json.loads(cmd.stdout)["hash"]
 
 
 def fix_plugin_name(name):
@@ -30,7 +52,7 @@ def fix_plugin_name(name):
 
 
 # generate plugins.nix code
-tree = etree.parse(qgis_plugins_xml)
+tree = etree.parse(plugins_xml)
 root = tree.getroot()
 
 print("{")  # opening curly
@@ -45,7 +67,11 @@ def fix_plugin_name(name):
         name = fix_plugin_name(plugin.attrib["name"])
         url = plugin.find("download_url").text
         version = plugin.find("version").text
-        hash = get_nix_hash(url)
+        hash = get_nix_hash(
+            qgis_package,
+            name,
+            version
+        )
 
         print(
             f"""

pkgs/qgis/update-plugins.sh

@@ -16,5 +16,7 @@ for package in "${QGIS_PACKAGES[@]}"; do
     echo -e "\nUpdating $package plugins ..."
     curl $QGIS_PLUGINS_XML_URL?qgis="$major_version" -o "$package"-plugins.xml
 
-    python ./update-plugins.py "$package"-plugins.xml > "$package"-plugins-list.nix
+    python ./update-plugins.py "$package"-plugins.xml > "$package"-plugins-list.nix.new
+    cp "$package"-plugins-list.nix.new "$package"-plugins-list.nix
+    rm "$package"-plugins-list.nix.new
 done