PR #1603: Disable -Wnon-virtual-dtor warning for CommandLineFlag implementations

Imported from GitHub PR https://github.com/abseil/abseil-cpp/pull/1603

Merge e324303b1f2aaee8e4418cffb838f150a2d4f4e7 into d8027081

Merging this change closes #1603

COPYBARA_INTEGRATE_REVIEW=https://github.com/abseil/abseil-cpp/pull/1603 from adgajda:master e324303b1f2aaee8e4418cffb838f150a2d4f4e7
PiperOrigin-RevId: 615522811
Change-Id: I46a388ac62ffd42ce175dbfa04e414dd498855f8

absl/copts/GENERATED_AbseilCopts.cmake

@@ -44,6 +44,7 @@ list(APPEND ABSL_GCC_FLAGS
     "-Wconversion-null"
     "-Wformat-security"
     "-Wmissing-declarations"
+    "-Wnon-virtual-dtor"
     "-Woverlength-strings"
     "-Wpointer-arith"
     "-Wundef"
@@ -61,6 +62,7 @@ list(APPEND ABSL_GCC_TEST_FLAGS
     "-Wcast-qual"
     "-Wconversion-null"
     "-Wformat-security"
+    "-Wnon-virtual-dtor"
     "-Woverlength-strings"
     "-Wpointer-arith"
     "-Wundef"

absl/copts/GENERATED_copts.bzl

@@ -45,6 +45,7 @@ ABSL_GCC_FLAGS = [
     "-Wconversion-null",
     "-Wformat-security",
     "-Wmissing-declarations",
+    "-Wnon-virtual-dtor",
     "-Woverlength-strings",
     "-Wpointer-arith",
     "-Wundef",
@@ -62,6 +63,7 @@ ABSL_GCC_TEST_FLAGS = [
     "-Wcast-qual",
     "-Wconversion-null",
     "-Wformat-security",
+    "-Wnon-virtual-dtor",
     "-Woverlength-strings",
     "-Wpointer-arith",
     "-Wundef",

absl/copts/copts.py

@@ -18,6 +18,7 @@ ABSL_GCC_FLAGS = [
     "-Wconversion-null",
     "-Wformat-security",
     "-Wmissing-declarations",
+    "-Wnon-virtual-dtor",
     "-Woverlength-strings",
     "-Wpointer-arith",
     "-Wundef",

absl/flags/commandlineflag.h

@@ -59,6 +59,14 @@ class PrivateHandleAccessor;
 //   // Now you can get flag info from that reflection handle.
 //   std::string flag_location = my_flag_data->Filename();
 //   ...
+
+// These are only used as constexpr global objects.
+// They do not use a virtual destructor to simplify their implementation.
+// They are not destroyed except at program exit, so leaks do not matter.
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
+#endif
 class CommandLineFlag {
  public:
   constexpr CommandLineFlag() = default;
@@ -193,6 +201,9 @@ class CommandLineFlag {
   // flag's value type.
   virtual void CheckDefaultValueParsingRoundtrip() const = 0;
 };
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
 
 ABSL_NAMESPACE_END
 }  // namespace absl

absl/flags/internal/flag.h

@@ -424,6 +424,13 @@ struct DynValueDeleter {
 
 class FlagState;
 
+// These are only used as constexpr global objects.
+// They do not use a virtual destructor to simplify their implementation.
+// They are not destroyed except at program exit, so leaks do not matter.
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
+#endif
 class FlagImpl final : public CommandLineFlag {
  public:
   constexpr FlagImpl(const char* name, const char* filename, FlagOpFn op,
@@ -623,6 +630,9 @@ class FlagImpl final : public CommandLineFlag {
   // problems.
   alignas(absl::Mutex) mutable char data_guard_[sizeof(absl::Mutex)];
 };
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
 
 ///////////////////////////////////////////////////////////////////////////////
 // The Flag object parameterized by the flag's value type. This class implements
@@ -753,8 +763,7 @@ void* FlagOps(FlagOp op, const void* v1, void* v2, void* v3) {
       // Round sizeof(FlagImp) to a multiple of alignof(FlagValue<T>) to get the
       // offset of the data.
       size_t round_to = alignof(FlagValue<T>);
-      size_t offset =
-          (sizeof(FlagImpl) + round_to - 1) / round_to * round_to;
+      size_t offset = (sizeof(FlagImpl) + round_to - 1) / round_to * round_to;
       return reinterpret_cast<void*>(offset);
     }
   }

absl/flags/reflection.cc

@@ -217,6 +217,13 @@ void FinalizeRegistry() {
 
 namespace {
 
+// These are only used as constexpr global objects.
+// They do not use a virtual destructor to simplify their implementation.
+// They are not destroyed except at program exit, so leaks do not matter.
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
+#endif
 class RetiredFlagObj final : public CommandLineFlag {
  public:
   constexpr RetiredFlagObj(const char* name, FlagFastTypeId type_id)
@@ -276,6 +283,9 @@ class RetiredFlagObj final : public CommandLineFlag {
   const char* const name_;
   const FlagFastTypeId type_id_;
 };
+#if defined(__GNUC__) && !defined(__clang__)
+#pragma GCC diagnostic pop
+#endif
 
 }  // namespace