build: add version checks to release script

Enhances the release script to check that the specified tag
is also the tag that is currently checked out. In addition to that, the
script also ensures that the tag and the version specified in version.go
match.

build/release/release.sh

@@ -16,6 +16,35 @@ if [[ $1x = x ]]; then
     TAG=$DATE-$VERSION
 else
     TAG=$1
+
+    # If a tag is specified, ensure that that tag is present and checked out.
+    if [[ $TAG != $(git tag -l --points-at HEAD) ]]; then
+        echo "tag $TAG not checked out"
+        exit 1
+    fi
+
+    # Build lnd to extract version.
+    go build github.com/lightningnetwork/lnd/cmd/lnd
+
+    # Extract version command output.
+    LND_VERSION_OUTPUT=`./lnd --version`
+
+    # Use a regex to isolate the version string.
+    LND_VERSION_REGEX="lnd version (.+) commit"
+    if [[ $LND_VERSION_OUTPUT =~ $LND_VERSION_REGEX ]]; then
+        # Prepend 'v' to match git tag naming scheme.
+        LND_VERSION="v${BASH_REMATCH[1]}"
+        echo "version: $LND_VERSION"
+
+        # Match git tag with lnd version.
+        if [[ $TAG != $LND_VERSION ]]; then
+            echo "lnd version $LND_VERSION does not match tag $TAG"
+            exit 1
+        fi
+    else
+        echo "malformed lnd version output"
+        exit 1
+    fi
 fi
 
 go mod vendor