dotnet-sdk: update.sh - allow early exit. If updating to the latest version, and the local expression already is the latest version, exit without regenerating everything.

pkgs/development/compilers/dotnet/update.sh

···
     major_minor=$(sed 's/^\([0-9]*\.[0-9]*\).*$/\1/' <<< "$sem_version")
     content=$(curl -sL https://dotnetcli.blob.core.windows.net/dotnet/release-metadata/"$major_minor"/releases.json)
     major_minor_patch=$([ "$patch_specified" == true ] && echo "$sem_version" || jq -r '."latest-release"' <<< "$content")
+    major_minor_underscore=${major_minor/./_}
 
     release_content=$(release "$content" "$major_minor_patch")
     aspnetcore_version=$(jq -r '."aspnetcore-runtime".version' <<< "$release_content")
     runtime_version=$(jq -r '.runtime.version' <<< "$release_content")
     sdk_version=$(jq -r '.sdk.version' <<< "$release_content")
 
+    # If patch was not specified, check if the package is already the latest version
+    # If it is, exit early
+    if [ "$patch_specified" == false ] && [ -f "./versions/${sem_version}.nix" ]; then
+        current_version=$(nix-instantiate --eval -E "(import ./versions/${sem_version}.nix { \
+            buildAspNetCore = { ... }: {}; \
+            buildNetRuntime = { ... }: {}; \
+            buildNetSdk = { version, ... }: version; \
+            icu = null; }).sdk_${major_minor_underscore}" | jq -r)
+
+        if [[ "$current_version" == "$sdk_version" ]]; then
+            echo "Nothing to update."
+            exit
+        fi
+    fi
+
     aspnetcore_files="$(release_files "$release_content" "aspnetcore-runtime")"
     runtime_files="$(release_files "$release_content" "runtime")"
     sdk_files="$(release_files "$release_content" "sdk")"
 
-    major_minor_underscore=${major_minor/./_}
     channel_version=$(jq -r '."channel-version"' <<< "$content")
     support_phase=$(jq -r '."support-phase"' <<< "$content")
     echo "{ buildAspNetCore, buildNetRuntime, buildNetSdk, icu }: