Add fmt/lint for trailing spaces

Makefile

@@ -79,6 +79,7 @@ endif
 .PHONY: fmt
 fmt: ## Format the source files
 	$(SHFMT_COMMAND) $(SHFMT_FLAGS) --write $(MAKEFILE_DIR)
+	hack/fmt-trailing-spaces.sh
 
 SHELLCHECK_COMMAND := $(shell which shellcheck)
 ifeq (, $(SHELLCHECK_COMMAND))
@@ -96,6 +97,7 @@ transform-al2-to-al2023:
 lint: lint-docs ## Check the source files for syntax and format issues
 	$(SHFMT_COMMAND) $(SHFMT_FLAGS) --diff $(MAKEFILE_DIR)
 	$(SHELLCHECK_COMMAND) --format gcc --severity error $(SHELL_FILES)
+	hack/lint-trailing-spaces.sh
 
 .PHONY: test
 test: ## run the test-harness

hack/fmt-trailing-spaces.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+cd $(dirname $0)/..
+
+OS=$(uname)
+for FILE in $(find . -type f -not -path "*/.git/*"); do
+  if git check-ignore --quiet "$FILE"; then
+    continue
+  fi
+  echo >&2 "$FILE"
+  if [ "$OS" = "Darwin" ]; then
+    # macOS sed doesn't support '-i'
+    sed 's/[[:space:]]*$//g' "$FILE" > "$FILE.tmp"
+    # macOS chmod doesn't support '--reference'
+    chmod "$(stat -f "%Mp%Lp" $FILE)" "$FILE.tmp"
+    mv "$FILE.tmp" "$FILE"
+  else
+    # assume we have a sane sed
+    sed -i 's/[[:space:]]*$//g' "$FILE"
+  fi
+done

hack/lint-trailing-spaces.sh

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+
+cd $(dirname $0)/..
+git diff-tree --check $(git hash-object -t tree /dev/null) HEAD