Export of internal Abseil changes

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803abc2dcad8b2354c988e9bf58dac4a17683832 by Gennadiy Rozental <rogeeff@google.com>:

Avoid warning when RTTI is not enabled.

PiperOrigin-RevId: 294247546

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5a7b0b4d07d1d6e56fbb0b0ffbf4f8fcab772dbf by Derek Mauro <dmauro@google.com>:

Add a public Abseil FAQ

PiperOrigin-RevId: 294226960

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6945c4a6df7d7679711fea31aacf4fba6ac7baa1 by Gennadiy Rozental <rogeeff@google.com>:

Re-enable type mismatch check, which works in all the cases including shared libraries.

We will use RTTI in case when our hand written approximation of it reports a type mismatch. This way we can ensure that if a flag is defined in one shared object and referenced in another we do not report spurious errors.

PiperOrigin-RevId: 293905563
GitOrigin-RevId: 803abc2dcad8b2354c988e9bf58dac4a17683832
Change-Id: I1a23776d227ed2734c2e7183323786b7a95c3cc7

1 files changed, 23 insertions, 22 deletions

diff --git a/absl/flags/internal/flag.cc b/absl/flags/internal/flag.cc
index 6ce7def2d3d2..cfc0cf4d93d1 100644
--- a/absl/flags/internal/flag.cc
+++ b/absl/flags/internal/flag.cc
@@ -56,6 +56,14 @@ bool ShouldValidateFlagValue(FlagOpFn flag_type_id) {
   return true;
 }
 
+#if defined(ABSL_FLAGS_INTERNAL_HAS_RTTI)
+bool MatchRuntimeTypeId(FlagOpFn lhs_type_id, FlagOpFn rhs_type_id) {
+  return RuntimeTypeId(lhs_type_id) == RuntimeTypeId(rhs_type_id);
+}
+#else
+bool MatchRuntimeTypeId(FlagOpFn, FlagOpFn) { return true; }
+#endif
+
 // RAII helper used to temporarily unlock and relock `absl::Mutex`.
 // This is used when we need to ensure that locks are released while
 // invoking user supplied callbacks and then reacquired, since callbacks may
@@ -133,6 +141,18 @@ void FlagImpl::Destroy() {
   is_data_guard_inited_ = false;
 }
 
+void FlagImpl::AssertValidType(const flags_internal::FlagOpFn op) const {
+  // `op` is the unmarshaling operation corresponding to the declaration
+  // visibile at the call site. `op_` is the Flag's defined unmarshalling
+  // operation. They must match for this operation to be well-defined.
+  if (ABSL_PREDICT_FALSE(op != op_) && !MatchRuntimeTypeId(op, op_)) {
+    ABSL_INTERNAL_LOG(
+        FATAL,
+        absl::StrCat("Flag '", Name(),
+                     "' is defined as one type and declared as another"));
+  }
+}
+
 std::unique_ptr<void, DynValueDeleter> FlagImpl::MakeInitValue() const {
   void* res = nullptr;
   if (DefaultKind() == FlagDefaultKind::kDynamicValue) {
@@ -219,7 +239,7 @@ bool FlagImpl::RestoreState(const void* value, bool modified,
     if (counter_ == counter) return false;
   }
 
-  Write(value, op_);
+  Write(value);
 
   {
     absl::MutexLock l(DataGuard());
@@ -254,18 +274,9 @@ bool FlagImpl::TryParse(void** dst, absl::string_view value,
   return true;
 }
 
-void FlagImpl::Read(void* dst, const flags_internal::FlagOpFn dst_op) const {
+void FlagImpl::Read(void* dst) const {
   absl::ReaderMutexLock l(DataGuard());
 
-  // `dst_op` is the unmarshaling operation corresponding to the declaration
-  // visibile at the call site. `op` is the Flag's defined unmarshalling
-  // operation. They must match for this operation to be well-defined.
-  if (ABSL_PREDICT_FALSE(dst_op != op_)) {
-    ABSL_INTERNAL_LOG(
-        ERROR,
-        absl::StrCat("Flag '", Name(),
-                     "' is defined as one type and declared as another"));
-  }
   CopyConstruct(op_, value_.dynamic, dst);
 }
 
@@ -286,19 +297,9 @@ void FlagImpl::StoreAtomic() {
 #endif
 }
 
-void FlagImpl::Write(const void* src, const flags_internal::FlagOpFn src_op) {
+void FlagImpl::Write(const void* src) {
   absl::MutexLock l(DataGuard());
 
-  // `src_op` is the marshalling operation corresponding to the declaration
-  // visible at the call site. `op` is the Flag's defined marshalling operation.
-  // They must match for this operation to be well-defined.
-  if (ABSL_PREDICT_FALSE(src_op != op_)) {
-    ABSL_INTERNAL_LOG(
-        ERROR,
-        absl::StrCat("Flag '", Name(),
-                     "' is defined as one type and declared as another"));
-  }
-
   if (ShouldValidateFlagValue(op_)) {
     void* obj = Clone(op_, src);
     std::string ignored_error;