common-updater-scripts/u-s-v: allow omitting version with --ignore-same-version

This is useful when wanting to update secondary hashes like `cargoDeps`.

pkgs/common-updater/scripts/update-source-version

@@ -13,6 +13,8 @@ usage() {
     echo "                              [--version-key=<version-key>] [--source-key=<source-key>]"
     echo "                              [--system=<system>] [--file=<file-to-update>] [--rev=<revision>]"
     echo "                              [--ignore-same-hash] [--ignore-same-version] [--print-changes]"
+    echo ""
+    echo "The <version> positional argument is also optional when passing --ignore-same-version."
 }
 
 ignoreSameVersion=
@@ -71,7 +73,13 @@ newUrl=${args[3]}
 # Third-party repositories might not accept arguments in their default.nix.
 importTree="(let tree = import ./.; in if builtins.isFunction tree then tree {} else tree)"
 
-if (( "${#args[*]}" < 2 )); then
+if [[ -z "$ignoreSameVersion" ]]; then
+    requiredArgs=2
+else
+    requiredArgs=1
+fi
+
+if (( "${#args[*]}" < $requiredArgs )); then
     echo "$scriptName: Too few arguments"
     usage
     exit 1
@@ -143,6 +151,10 @@ if [[ -z "$oldVersion" ]]; then
     die "Couldn't find out the old version of '$attr'!"
 fi
 
+if [[ -n "$ignoreSameVersion" && -z "$newVersion" ]]; then
+    newVersion="$oldVersion"
+fi
+
 if [[ -z "$ignoreSameVersion" && "$oldVersion" = "$newVersion" ]]; then
     echo "$scriptName: New version same as old version, nothing to do." >&2
     if [ -n "$printChanges" ]; then