From fba7be80eb0fab54b570623d3991739cf3da0759 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Mon, 3 Apr 2023 18:11:42 +0200
Subject: [PATCH] Enable -Werror=switch-enum

switch statements must now match all enum values or disable the
warning.

Explicit is good. This has helped us find two bugs, after solving
another one by debugging.

From now on, adding to an enum will raise errors where they are
not explicitly handled, which is good for productivity, and helps
us decide the correct behavior in all usages.

Notably still excluded from this though are the cases where the
warning is disabled by local pragmas.

fromTOML.cc did not build despite a top-level pragma, so I've had
to resort to a makefile solution for that.
---
 local.mk               | 4 +++-
 mk/patterns.mk         | 4 ++--
 src/libexpr/local.mk   | 2 ++
 src/libutil/logging.cc | 2 +-
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/local.mk b/local.mk
index 6a7074e8e..6951c179e 100644
--- a/local.mk
+++ b/local.mk
@@ -1,6 +1,8 @@
 clean-files += Makefile.config
 
-GLOBAL_CXXFLAGS += -Wno-deprecated-declarations
+GLOBAL_CXXFLAGS += -Wno-deprecated-declarations -Werror=switch
+# Allow switch-enum to be overridden for files that do not support it, usually because of dependency headers.
+ERROR_SWITCH_ENUM = -Werror=switch-enum
 
 $(foreach i, config.h $(wildcard src/lib*/*.hh), \
   $(eval $(call install-file-in, $(i), $(includedir)/nix, 0644)))
diff --git a/mk/patterns.mk b/mk/patterns.mk
index 86a724806..c81150260 100644
--- a/mk/patterns.mk
+++ b/mk/patterns.mk
@@ -1,10 +1,10 @@
 $(buildprefix)%.o: %.cc
 	@mkdir -p "$(dir $@)"
-	$(trace-cxx) $(CXX) -o $@ -c $< $(CPPFLAGS) $(GLOBAL_CXXFLAGS_PCH) $(GLOBAL_CXXFLAGS) $(CXXFLAGS) $($@_CXXFLAGS) -MMD -MF $(call filename-to-dep, $@) -MP
+	$(trace-cxx) $(CXX) -o $@ -c $< $(CPPFLAGS) $(GLOBAL_CXXFLAGS_PCH) $(GLOBAL_CXXFLAGS) $(CXXFLAGS) $($@_CXXFLAGS) $(ERROR_SWITCH_ENUM) -MMD -MF $(call filename-to-dep, $@) -MP
 
 $(buildprefix)%.o: %.cpp
 	@mkdir -p "$(dir $@)"
-	$(trace-cxx) $(CXX) -o $@ -c $< $(CPPFLAGS) $(GLOBAL_CXXFLAGS_PCH) $(GLOBAL_CXXFLAGS) $(CXXFLAGS) $($@_CXXFLAGS) -MMD -MF $(call filename-to-dep, $@) -MP
+	$(trace-cxx) $(CXX) -o $@ -c $< $(CPPFLAGS) $(GLOBAL_CXXFLAGS_PCH) $(GLOBAL_CXXFLAGS) $(CXXFLAGS) $($@_CXXFLAGS) $(ERROR_SWITCH_ENUM) -MMD -MF $(call filename-to-dep, $@) -MP
 
 $(buildprefix)%.o: %.c
 	@mkdir -p "$(dir $@)"
diff --git a/src/libexpr/local.mk b/src/libexpr/local.mk
index 2171e769b..d243b9cec 100644
--- a/src/libexpr/local.mk
+++ b/src/libexpr/local.mk
@@ -46,3 +46,5 @@ $(foreach i, $(wildcard src/libexpr/flake/*.hh), \
 $(d)/primops.cc: $(d)/imported-drv-to-derivation.nix.gen.hh $(d)/primops/derivation.nix.gen.hh $(d)/fetchurl.nix.gen.hh
 
 $(d)/flake/flake.cc: $(d)/flake/call-flake.nix.gen.hh
+
+src/libexpr/primops/fromTOML.o:	ERROR_SWITCH_ENUM =
diff --git a/src/libutil/logging.cc b/src/libutil/logging.cc
index 741e1d1f5..5a2dd99af 100644
--- a/src/libutil/logging.cc
+++ b/src/libutil/logging.cc
@@ -68,7 +68,7 @@ public:
             case lvlNotice: case lvlInfo: c = '5'; break;
             case lvlTalkative: case lvlChatty: c = '6'; break;
             case lvlDebug: case lvlVomit: c = '7';
-            default: c = '7'; break;
+            default: c = '7'; break; // should not happen, and missing enum case is reported by -Werror=switch-enum
             }
             prefix = std::string("<") + c + ">";
         }