From 27c983b5d0c5c9bf788fc3a34b2df4c7202f8097 Mon Sep 17 00:00:00 2001
From: htuch <htuch@users.noreply.github.com>
Date: Tue, 6 Feb 2018 13:19:54 -0500
Subject: [PATCH] build: retrigger external builds when CFLAGS/CXXFLAGS
 changes. (#2534)

This was a longstanding problem with external deps that manifested in
https://github.com/google/oss-fuzz/pull/1130.

Signed-off-by: Harvey Tuch <htuch@google.com>
---
 bazel/repositories.bzl      |  2 ++
 ci/build_container/Makefile | 14 +++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/bazel/repositories.bzl b/bazel/repositories.bzl
index dccf3bb3f77d..de5f7a127a85 100644
--- a/bazel/repositories.bzl
+++ b/bazel/repositories.bzl
@@ -141,6 +141,8 @@ def envoy_dependencies(path = "@envoy_deps//", skip_targets = []):
         environ = [
             "CC",
             "CXX",
+            "CFLAGS",
+            "CXXFLAGS",
             "LD_LIBRARY_PATH"
         ],
         # Don't pretend we're in the sandbox, we do some evil stuff with envoy_dep_cache.
diff --git a/ci/build_container/Makefile b/ci/build_container/Makefile
index beeee641058e..b80fa664444d 100644
--- a/ci/build_container/Makefile
+++ b/ci/build_container/Makefile
@@ -13,6 +13,10 @@ CXXFLAGS ?= -ggdb3 -fno-omit-frame-pointer -O2
 CFLAGS ?= -ggdb3 -fno-omit-frame-pointer -O2
 CPPFLAGS ?= -DNDEBUG
 
+# Keep track of the env vars we depend upon for $(THIRDPARTY_DEPS)/%.dep.env. If the list (captured
+# above) of flags changes, this should be updated.
+ENV_STR := $(CC) $(CXX) $(CXXFLAGS) $(CFLAGS) $(CPPFLAGS)
+
 # If $(BUILD_DISTINCT) is set in the make environment, the artifacts are built and installed in
 # distinct directories under $(THIRDPARTY_BUILD) and $(THIRDPARTY_SRC). They end up looking like
 # $(THIRDPARTY_BUILD)/protobuf.dep/include, etc. instead of all being under
@@ -47,7 +51,15 @@ build-recipe = cd "$(THIRDPARTY_SRC)" && \
 	   bash -c "time $(CURDIR)/recipe_wrapper.sh $(realpath $<)" 2>&1) > $@.log) || (cat $@.log; exit 1)) && \
 	$(build-complete)
 
-$(THIRDPARTY_DEPS)/%.dep: $(RECIPES)/%.sh
+# Simplify wildcard phony with FORCE target.
+.PHONY: FORCE
+FORCE:
+
+# Capture $(ENV_STR) deps to retrigger build when they change.
+$(THIRDPARTY_DEPS)/%.dep.env: FORCE
+	@[ "$(cat $@)" != "$(ENV_STR)" ] && echo "$(ENV_STR)" > $@
+
+$(THIRDPARTY_DEPS)/%.dep: $(RECIPES)/%.sh $(THIRDPARTY_DEPS)/%.dep.env
 	@+$(call build-recipe,)
 
 # Special support for targets that need protobuf, and hence take a dependency on protobuf.dep.