guix: Add more sanity checks to guix-build.sh

contrib/guix/guix-build.sh

@@ -6,6 +6,20 @@ set -e -o pipefail
 ## Sanity Checks ##
 ###################
 
+################
+# Check 1: Make sure that we can invoke required tools
+################
+for cmd in git make guix cat mkdir; do
+    if ! command -v "$cmd" > /dev/null 2>&1; then
+        echo "ERR: This script requires that '$cmd' is installed and available in your \$PATH"
+        exit 1
+    fi
+done
+
+################
+# Check 2: Make sure GUIX_BUILD_OPTIONS is empty
+################
+#
 # GUIX_BUILD_OPTIONS is an environment variable recognized by guix commands that
 # can perform builds. This seems like what we want instead of
 # ADDITIONAL_GUIX_COMMON_FLAGS, but the value of GUIX_BUILD_OPTIONS is actually
@@ -30,6 +44,26 @@ EOF
 exit 1
 fi
 
+################
+# Check 3: Make sure that we're not in a dirty worktree
+################
+if ! git diff-index --quiet HEAD -- && [ -z "$FORCE_DIRTY_WORKTREE" ]; then
+cat << EOF
+ERR: The current git worktree is dirty, which may lead to broken builds.
+
+     Aborting...
+
+Hint: To make your git worktree clean, You may want to:
+      1. Commit your changes,
+      2. Stash your changes, or
+      3. Set the 'FORCE_DIRTY_WORKTREE' environment variable if you insist on
+         using a dirty worktree
+EOF
+exit 1
+else
+    GIT_COMMIT=$(git rev-parse --short=12 HEAD)
+fi
+
 #########
 # Setup #
 #########