From 22353e9e1ed5bf8bc5bad179896ca2877f7511e2 Mon Sep 17 00:00:00 2001
From: Angus Gratton <angus@redyak.com.au>
Date: Tue, 14 Jan 2025 11:50:27 +1100
Subject: [PATCH] py/mkrules: Add GIT_SUBMODULES_FAIL_IF_EMPTY flag for CMake
 ports.

The way CMake gathers the submodule list, it can quietly be empty
if the previous step fails. This makes it an explicit error.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>
---
 ports/esp32/Makefile | 2 +-
 ports/rp2/Makefile   | 2 +-
 py/mkrules.mk        | 7 +++++++
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/ports/esp32/Makefile b/ports/esp32/Makefile
index 1c2fa82ce..1ce4d9720 100644
--- a/ports/esp32/Makefile
+++ b/ports/esp32/Makefile
@@ -114,4 +114,4 @@ size-files:
 submodules:
 	@GIT_SUBMODULES=$$(IDF_COMPONENT_MANAGER=0 idf.py $(IDFPY_FLAGS) -B $(BUILD)/submodules -D ECHO_SUBMODULES=1 build 2>&1 | \
 	                  grep '^GIT_SUBMODULES=' | cut -d= -f2); \
-	$(MAKE) -f ../../py/mkrules.mk GIT_SUBMODULES="$${GIT_SUBMODULES}" submodules
+	$(MAKE) -f ../../py/mkrules.mk GIT_SUBMODULES="$${GIT_SUBMODULES}" GIT_SUBMODULES_FAIL_IF_EMPTY=1 submodules
diff --git a/ports/rp2/Makefile b/ports/rp2/Makefile
index afa21cc7a..200899d33 100644
--- a/ports/rp2/Makefile
+++ b/ports/rp2/Makefile
@@ -76,4 +76,4 @@ submodules:
 	$(MAKE) -f ../../py/mkrules.mk GIT_SUBMODULES="lib/pico-sdk" submodules
 	@GIT_SUBMODULES=$$(cmake -B $(BUILD)/submodules -DECHO_SUBMODULES=1 ${CMAKE_ARGS} -S . 2>&1 | \
 	                  grep '^GIT_SUBMODULES=' | cut -d= -f2); \
-	$(MAKE) -f ../../py/mkrules.mk GIT_SUBMODULES="$${GIT_SUBMODULES}" submodules
+	$(MAKE) -f ../../py/mkrules.mk GIT_SUBMODULES="$${GIT_SUBMODULES}" GIT_SUBMODULES_FAIL_IF_EMPTY=1 submodules
diff --git a/py/mkrules.mk b/py/mkrules.mk
index 74978b0d1..373bda899 100644
--- a/py/mkrules.mk
+++ b/py/mkrules.mk
@@ -257,6 +257,13 @@ ifneq ($(GIT_SUBMODULES),)
 	$(Q)cd $(TOP) && git submodule sync $(GIT_SUBMODULES)
 	$(Q)cd $(TOP) && git submodule update --init --filter=blob:none $(GIT_SUBMODULES) || \
 	  git submodule update --init $(GIT_SUBMODULES)
+else
+ifeq ($(GIT_SUBMODULES_FAIL_IF_EMPTY),1)
+	# If you see this error, it may mean the internal step run by the port's build
+	# system to find git submodules has failed. Double-check dependencies are set correctly.
+	$(ECHO) "Internal build error: The submodule list should not be empty."
+	exit 1
+endif
 endif
 .PHONY: submodules