From 4b291ddf4bdd5c29c58ea153761ade7a9f4e1d92 Mon Sep 17 00:00:00 2001
From: Richard Barnes <rbarnes@umn.edu>
Date: Tue, 30 Jul 2024 12:26:04 -0700
Subject: [PATCH] Make fallthroughs explicit and enable warnings around this

---
 CMakeLists.txt     | 4 ++--
 core/desugarer.cpp | 2 +-
 core/vm.cpp        | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 213539449..84e554b6a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -36,8 +36,8 @@ set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${GLOBAL_OUTPUT_PATH})
 if (${CMAKE_CXX_COMPILER_ID} MATCHES "Clang" OR
         ${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")
     set(OPT "-O3")
-    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -g -Wall -Wextra -pedantic -std=c99 -O3 ${OPT}")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g -Wall -Wextra -Woverloaded-virtual -pedantic -std=c++17 -fPIC ${OPT}")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -g -Wall -Wextra -Wimplicit-fallthrough -pedantic -std=c99 -O3 ${OPT}")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g -Wall -Wextra -Wimplicit-fallthrough -Woverloaded-virtual -pedantic -std=c++17 -fPIC ${OPT}")
 else()
     # TODO: Windows support.
     message(FATAL_ERROR "Compiler ${CMAKE_CXX_COMPILER_ID} not supported")
diff --git a/core/desugarer.cpp b/core/desugarer.cpp
index 6c38eb913..611c1545e 100644
--- a/core/desugarer.cpp
+++ b/core/desugarer.cpp
@@ -732,7 +732,7 @@ class Desugarer {
                 } break;
 
                 case BOP_MANIFEST_UNEQUAL: invert = true;
-                /* fallthrough */
+                [[fallthrough]];
                 case BOP_MANIFEST_EQUAL: {
                     ast_ = equals(ast->location, ast->left, ast->right);
                     if (invert)
diff --git a/core/vm.cpp b/core/vm.cpp
index 0e21c82aa..7cc0a8655 100644
--- a/core/vm.cpp
+++ b/core/vm.cpp
@@ -2390,7 +2390,7 @@ class Interpreter {
                     stack.top().val2 = scratch;
                     stack.top().kind = FRAME_BINARY_OP;
                 }
-                // Falls through.
+                [[fallthrough]];
                 case FRAME_BINARY_OP: {
                     const auto &ast = *static_cast<const Binary *>(f.ast);
                     const Value &lhs = stack.top().val;