From a82aeedb5b9e24c9788febab3dcf65169b79cece Mon Sep 17 00:00:00 2001
From: Jade Lovelace <software@lfcode.ca>
Date: Sat, 24 Feb 2024 15:52:16 -0800
Subject: [PATCH] Warn on implicit switch case fallthrough

This seems to have found one actual bug in fs-sink.cc: the symlink case
was falling into the regular file case, which can't possibly be
intentional, right?
---
 Makefile               | 2 +-
 src/libexpr/lexer.l    | 3 +++
 src/libutil/fs-sink.cc | 2 ++
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index d3542c3e981..f8689c8cff2 100644
--- a/Makefile
+++ b/Makefile
@@ -81,7 +81,7 @@ ifdef HOST_WINDOWS
   GLOBAL_LDFLAGS += -Wl,--export-all-symbols
 endif
 
-GLOBAL_CXXFLAGS += -g -Wall -include $(buildprefix)config.h -std=c++2a -I src
+GLOBAL_CXXFLAGS += -g -Wall -Wimplicit-fallthrough -include $(buildprefix)config.h -std=c++2a -I src
 
 # Include the main lib, causing rules to be defined
 
diff --git a/src/libexpr/lexer.l b/src/libexpr/lexer.l
index 380048c77e2..5b26d6927de 100644
--- a/src/libexpr/lexer.l
+++ b/src/libexpr/lexer.l
@@ -94,6 +94,9 @@ static StringToken unescapeStr(SymbolTable & symbols, char * s, size_t length)
 
 }
 
+// yacc generates code that uses unannotated fallthrough.
+#pragma GCC diagnostic ignored "-Wimplicit-fallthrough"
+
 #define YY_USER_INIT initLoc(yylloc)
 #define YY_USER_ACTION adjustLoc(yylloc, yytext, yyleng);
 
diff --git a/src/libutil/fs-sink.cc b/src/libutil/fs-sink.cc
index 95b6088da9e..35ce0ac3611 100644
--- a/src/libutil/fs-sink.cc
+++ b/src/libutil/fs-sink.cc
@@ -15,6 +15,7 @@ void copyRecursive(
     case SourceAccessor::tSymlink:
     {
         sink.createSymlink(to, accessor.readLink(from));
+        break;
     }
 
     case SourceAccessor::tRegular:
@@ -38,6 +39,7 @@ void copyRecursive(
                 sink, to + "/" + name);
             break;
         }
+        break;
     }
 
     case SourceAccessor::tMisc: