GODRIVER-3329 Update the check-modules make target to include submodules

Makefile

@@ -48,14 +48,9 @@ install-lll:
 check-fmt: install-lll
 	etc/check_fmt.sh
 
-# check-modules runs "go mod tidy"  and exits with a non-zero exit code if there
-# are any module changes. The intent is to confirm that exactly the required
-# modules are declared as dependencies. We should always be able to run "go mod
-# tidy" and expect that no unrelated changes are made to the "go.mod" file.
 .PHONY: check-modules
 check-modules:
-	go mod tidy -v
-	git diff --exit-code go.mod go.sum
+	etc/check_modules.sh
 
 .PHONY: doc
 doc:

etc/check_modules.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+# check-modules runs "go mod tidy" on each module and exits with a non-zero exit code if there
+# are any module changes. The intent is to confirm that exactly the required
+# modules are declared as dependencies. We should always be able to run "go mod
+# tidy" and expect that no unrelated changes are made to the "go.mod" file.
+set -eu
+
+mods=$(find . -name go.mod)
+for mod in $mods; do
+  pushd $(dirname $mod) > /dev/null
+  echo "Checking $mod..."
+  go mod tidy -v
+  git diff --exit-code go.mod go.sum
+  echo "Checking $mod... done"
+  popd > /dev/null
+done