New switch idiom

Add -Wswitch-enum -Werror=switch-enum to enforce that we explicitly
handle all cases, and add a default: __builtin_unreachable() to all
switches to make un-enumerated values UB

CMakeLists.txt

@@ -22,7 +22,8 @@ if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
                                                "MinSizeRel" "RelWithDebInfo")
 endif()
 
-add_compile_options(-fdata-sections -ffunction-sections -fstrict-enums)
+add_compile_options(-fdata-sections -ffunction-sections -Wswitch-enum
+                    -Werror=switch-enum)
 
 # This is encouraged according to
 # https://valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.clientreq

ConflictSet.cpp

@@ -382,8 +382,9 @@ uint8_t *Node::partialKey() {
     return ((Node48 *)this)->partialKey();
   case Type_Node256:
     return ((Node256 *)this)->partialKey();
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
-  __builtin_unreachable(); // GCOVR_EXCL_LINE
 }
 
 struct NodeAllocators {
@@ -478,8 +479,9 @@ Node *&getChildExists(Node *self, uint8_t index) {
     assert(self256->bitSet.test(index));
     return self256->children[index].child;
   }
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
-  __builtin_unreachable(); // GCOVR_EXCL_LINE
 }
 
 // Precondition - an entry for index must exist in the node
@@ -510,8 +512,9 @@ Node *getChild(Node *self, uint8_t index) {
     auto *self256 = static_cast<Node256 *>(self);
     return self256->children[index].child;
   }
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
-  __builtin_unreachable(); // GCOVR_EXCL_LINE
 }
 
 template <class NodeT> int getChildGeqSimd(NodeT *self, int child) {
@@ -590,8 +593,9 @@ int getChildGeq(Node *self, int child) {
     auto *self48 = static_cast<Node48 *>(self);
     return self48->bitSet.firstSetGeq(child);
   }
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
-  __builtin_unreachable(); // GCOVR_EXCL_LINE
 }
 
 void setChildrenParents(Node3 *n) {
@@ -652,6 +656,8 @@ Node *&getOrCreateChild(Node *&self, uint8_t index,
       return result;
     }
   } break;
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
 
   switch (self->type) {
@@ -783,8 +789,9 @@ Node *&getOrCreateChild(Node *&self, uint8_t index,
     self256->bitSet.set(index);
     return self256->children[index].child;
   }
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
-  __builtin_unreachable(); // GCOVR_EXCL_LINE
 }
 
 Node *nextPhysical(Node *node) {
@@ -917,6 +924,8 @@ void freeAndMakeCapacityAtLeast(Node *&self, int capacity,
     }
     self = newSelf;
   } break;
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
 }
 
@@ -1063,6 +1072,8 @@ void maybeDownsize(Node *self, NodeAllocators *allocators,
       allocators->node256.release(self256);
     }
     break;
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
 }
 
@@ -1111,6 +1122,8 @@ Node *erase(Node *self, NodeAllocators *allocators, ConflictSet::Impl *impl,
   case Type_Node256:
     allocators->node256.release((Node256 *)self);
     break;
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
 
   switch (parent->type) {
@@ -1158,6 +1171,8 @@ Node *erase(Node *self, NodeAllocators *allocators, ConflictSet::Impl *impl,
     parent256->bitSet.reset(parentsIndex);
     parent256->children[parentsIndex].child = nullptr;
   } break;
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
 
   --parent->numChildren;
@@ -1508,6 +1523,8 @@ int64_t maxBetweenExclusive(Node *n, int begin, int end) {
         begin, end);
     break;
   }
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
 #if DEBUG_VERBOSE && !defined(NDEBUG)
   fprintf(stderr, "At `%s', max version in (%02x, %02x) is %" PRId64 "\n",
@@ -1711,7 +1728,7 @@ struct CheckRangeLeftSide {
       }
       break;
     }
-    case DownLeftSpine:
+    case DownLeftSpine: {
       if (n->entryPresent) {
         ok = n->entry.rangeVersion <= readVersion;
         return true;
@@ -1719,7 +1736,9 @@ struct CheckRangeLeftSide {
       int c = getChildGeq(n, 0);
       assert(c >= 0);
       n = getChildExists(n, c);
-      break;
+    } break;
+    default:
+      __builtin_unreachable(); // GCOVR_EXCL_LINE
     }
     return false;
   }
@@ -1837,7 +1856,7 @@ struct CheckRangeRightSide {
         }
       }
     } break;
-    case DownLeftSpine:
+    case DownLeftSpine: {
       if (n->entryPresent) {
         ok = n->entry.rangeVersion <= readVersion;
         return true;
@@ -1845,7 +1864,9 @@ struct CheckRangeRightSide {
       int c = getChildGeq(n, 0);
       assert(c >= 0);
       n = getChildExists(n, c);
-      break;
+    } break;
+    default:
+      __builtin_unreachable(); // GCOVR_EXCL_LINE
     }
     return false;
   }
@@ -2380,8 +2401,9 @@ int64_t &maxVersion(Node *n, ConflictSet::Impl *impl) {
     assert(n256->bitSet.test(index));
     return n256->children[index].childMaxVersion;
   }
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
-  __builtin_unreachable(); // GCOVR_EXCL_LINE
 }
 
 Node *&getInTree(Node *n, ConflictSet::Impl *impl) {
@@ -2651,6 +2673,8 @@ Iterator firstGeq(Node *n, std::string_view key) {
   case Type_Node256:
     minNumChildren = kMinChildrenNode256;
     break;
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
   if (node->numChildren + int(node->entryPresent) < minNumChildren) {
     fprintf(stderr,
@@ -2708,8 +2732,9 @@ int64_t getNodeSize(struct Node *n) {
     return sizeof(Node48);
   case Type_Node256:
     return sizeof(Node256);
+  default:
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
-  __builtin_unreachable(); // GCOVR_EXCL_LINE
 }
 
 int64_t getSearchPathLength(Node *n) {