Export of internal Abseil changes

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b770d03c2f1042d399c3f9576e881691cbe962c4 by Abseil Team <absl-team@google.com>:

Avoid applying the workaround for MSVC's static initialization problems when using clang-cl.

PiperOrigin-RevId: 275870089

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2b8fc02ec49aeb5ad56cef20259cdd7f6ee0c917 by Abseil Team <absl-team@google.com>:

Document return values.

PiperOrigin-RevId: 275839042

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baa99064f9a28b188661df7fba989fcd558818af by Abseil Team <absl-team@google.com>:

Support "auto" and other uncommon builtin types in absl::debugging_internal::Demangle.

PiperOrigin-RevId: 275556195

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f9d5c6a3a0d374dbf105d6e2e9e0c8fa949ed187 by Gennadiy Rozental <rogeeff@google.com>:

Internal rework.

PiperOrigin-RevId: 275550005

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2679a77db5b26349e8c8b2059621af55d2fca139 by Mark Barolak <mbar@google.com>:

Remove a comment reference to the no longer extant ::string implementation.

PiperOrigin-RevId: 275531987

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7b427a7613c44a98c6f13da43b2bff2837ca6b19 by Derek Mauro <dmauro@google.com>:

Upgrade to Bazel 1.0.0 and CMake 3.15.4

PiperOrigin-RevId: 275500823

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81f7d20905debf9d1e300bd2e9899f88d27f632a by Derek Mauro <dmauro@google.com>:

Fix -Wimplicit-int-float-conversion warning in latest clang

PiperOrigin-RevId: 275492439
GitOrigin-RevId: b770d03c2f1042d399c3f9576e881691cbe962c4
Change-Id: I9b39dad524489f0d62c912d02e8ac43761c81e55

1 files changed, 316 insertions, 21 deletions

diff --git a/absl/flags/internal/flag.cc b/absl/flags/internal/flag.cc
index 0f4035819cdb..061113d76557 100644
--- a/absl/flags/internal/flag.cc
+++ b/absl/flags/internal/flag.cc
@@ -15,36 +15,331 @@
 
 #include "absl/flags/internal/flag.h"
 
+#include "absl/base/optimization.h"
 #include "absl/synchronization/mutex.h"
 
 namespace absl {
 namespace flags_internal {
+namespace {
 
-// If the flag has a mutation callback this function invokes it. While the
-// callback is being invoked the primary flag's mutex is unlocked and it is
-// re-locked back after call to callback is completed. Callback invocation is
-// guarded by flag's secondary mutex instead which prevents concurrent
-// callback invocation. Note that it is possible for other thread to grab the
-// primary lock and update flag's value at any time during the callback
-// invocation. This is by design. Callback can get a value of the flag if
-// necessary, but it might be different from the value initiated the callback
-// and it also can be different by the time the callback invocation is
-// completed. Requires that *primary_lock be held in exclusive mode; it may be
-// released and reacquired by the implementation.
-void InvokeCallback(absl::Mutex* primary_mu, absl::Mutex* callback_mu,
-                    FlagCallback cb) ABSL_EXCLUSIVE_LOCKS_REQUIRED(primary_mu) {
-  if (!cb) return;
-
-  // When executing the callback we need the primary flag's mutex to be
-  // unlocked so that callback can retrieve the flag's value.
-  primary_mu->Unlock();
+// Currently we only validate flag values for user-defined flag types.
+bool ShouldValidateFlagValue(const CommandLineFlag& flag) {
+#define DONT_VALIDATE(T) \
+  if (flag.IsOfType<T>()) return false;
+  ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(DONT_VALIDATE)
+  DONT_VALIDATE(std::string)
+  DONT_VALIDATE(std::vector<std::string>)
+#undef DONT_VALIDATE
 
+  return true;
+}
+
+}  // namespace
+
+void FlagImpl::Init() {
+  ABSL_CONST_INIT static absl::Mutex init_lock(absl::kConstInit);
+
+  {
+    absl::MutexLock lock(&init_lock);
+
+    if (locks_ == nullptr) {  // Must initialize Mutexes for this flag.
+      locks_ = new FlagImpl::CommandLineFlagLocks;
+    }
+  }
+
+  absl::MutexLock lock(&locks_->primary_mu);
+
+  if (def_ != nullptr) {
+    inited_.store(true, std::memory_order_release);
+  } else {
+    // Need to initialize def and cur fields.
+    def_ = (*initial_value_gen_)();
+    cur_ = Clone(op_, def_);
+    StoreAtomic();
+    inited_.store(true, std::memory_order_release);
+    InvokeCallback();
+  }
+}
+
+// Ensures that the lazily initialized data is initialized,
+// and returns pointer to the mutex guarding flags data.
+absl::Mutex* FlagImpl::DataGuard() const
+    ABSL_LOCK_RETURNED(locks_->primary_mu) {
+  if (ABSL_PREDICT_FALSE(!inited_.load(std::memory_order_acquire))) {
+    const_cast<FlagImpl*>(this)->Init();
+  }
+
+  // All fields initialized; locks_ is therefore safe to read.
+  return &locks_->primary_mu;
+}
+
+void FlagImpl::Destroy() const {
   {
-    absl::MutexLock lock(callback_mu);
-    cb();
+    absl::MutexLock l(DataGuard());
+
+    // Values are heap allocated for Abseil Flags.
+    if (cur_) Delete(op_, cur_);
+    if (def_) Delete(op_, def_);
   }
 
-  primary_mu->Lock();
+  delete locks_;
+}
+
+bool FlagImpl::IsModified() const {
+  absl::MutexLock l(DataGuard());
+  return modified_;
+}
+
+bool FlagImpl::IsSpecifiedOnCommandLine() const {
+  absl::MutexLock l(DataGuard());
+  return on_command_line_;
+}
+
+std::string FlagImpl::DefaultValue() const {
+  absl::MutexLock l(DataGuard());
+
+  return Unparse(marshalling_op_, def_);
+}
+
+std::string FlagImpl::CurrentValue() const {
+  absl::MutexLock l(DataGuard());
+
+  return Unparse(marshalling_op_, cur_);
+}
+
+void FlagImpl::SetCallback(
+    const flags_internal::FlagCallback mutation_callback) {
+  absl::MutexLock l(DataGuard());
+
+  callback_ = mutation_callback;
+
+  InvokeCallback();
+}
+
+void FlagImpl::InvokeCallback() const
+    ABSL_EXCLUSIVE_LOCKS_REQUIRED(locks_->primary_mu) {
+  if (!callback_) return;
+
+  // If the flag has a mutation callback this function invokes it. While the
+  // callback is being invoked the primary flag's mutex is unlocked and it is
+  // re-locked back after call to callback is completed. Callback invocation is
+  // guarded by flag's secondary mutex instead which prevents concurrent
+  // callback invocation. Note that it is possible for other thread to grab the
+  // primary lock and update flag's value at any time during the callback
+  // invocation. This is by design. Callback can get a value of the flag if
+  // necessary, but it might be different from the value initiated the callback
+  // and it also can be different by the time the callback invocation is
+  // completed. Requires that *primary_lock be held in exclusive mode; it may be
+  // released and reacquired by the implementation.
+  DataGuard()->Unlock();
+
+  {
+    absl::MutexLock lock(&locks_->callback_mu);
+    callback_();
+  }
+
+  DataGuard()->Lock();
+}
+
+bool FlagImpl::RestoreState(const CommandLineFlag& flag, const void* value,
+                            bool modified, bool on_command_line,
+                            int64_t counter) {
+  {
+    absl::MutexLock l(DataGuard());
+
+    if (counter_ == counter) return false;
+  }
+
+  Write(flag, value, op_);
+
+  {
+    absl::MutexLock l(DataGuard());
+
+    modified_ = modified;
+    on_command_line_ = on_command_line;
+  }
+
+  return true;
+}
+
+// Attempts to parse supplied `value` string using parsing routine in the `flag`
+// argument. If parsing successful, this function stores the parsed value in
+// 'dst' assuming it is a pointer to the flag's value type. In case if any error
+// is encountered in either step, the error message is stored in 'err'
+bool FlagImpl::TryParse(const CommandLineFlag& flag, void* dst,
+                        absl::string_view value, std::string* err) const
+    ABSL_EXCLUSIVE_LOCKS_REQUIRED(locks_->primary_mu) {
+  void* tentative_value = Clone(op_, def_);
+  std::string parse_err;
+  if (!Parse(marshalling_op_, value, tentative_value, &parse_err)) {
+    auto type_name = flag.Typename();
+    absl::string_view err_sep = parse_err.empty() ? "" : "; ";
+    absl::string_view typename_sep = type_name.empty() ? "" : " ";
+    *err = absl::StrCat("Illegal value '", value, "' specified for",
+                        typename_sep, type_name, " flag '", flag.Name(), "'",
+                        err_sep, parse_err);
+    Delete(op_, tentative_value);
+    return false;
+  }
+
+  Copy(op_, tentative_value, dst);
+  Delete(op_, tentative_value);
+  return true;
+}
+
+void FlagImpl::Read(const CommandLineFlag& flag, void* dst,
+                    const flags_internal::FlagOpFn dst_op) 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 '", flag.Name(),
+                     "' is defined as one type and declared as another"));
+  }
+  CopyConstruct(op_, cur_, dst);
+}
+
+void FlagImpl::StoreAtomic() ABSL_EXCLUSIVE_LOCKS_REQUIRED(locks_->primary_mu) {
+  size_t data_size = Sizeof(op_);
+
+  if (data_size <= sizeof(int64_t)) {
+    int64_t t = 0;
+    std::memcpy(&t, cur_, data_size);
+    atomic_.store(t, std::memory_order_release);
+  }
+}
+
+void FlagImpl::Write(const CommandLineFlag& flag, const void* src,
+                     const flags_internal::FlagOpFn src_op) {
+  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 '", flag.Name(),
+                     "' is defined as one type and declared as another"));
+  }
+
+  if (ShouldValidateFlagValue(flag)) {
+    void* obj = Clone(op_, src);
+    std::string ignored_error;
+    std::string src_as_str = Unparse(marshalling_op_, src);
+    if (!Parse(marshalling_op_, src_as_str, obj, &ignored_error)) {
+      ABSL_INTERNAL_LOG(ERROR,
+                        absl::StrCat("Attempt to set flag '", flag.Name(),
+                                     "' to invalid value ", src_as_str));
+    }
+    Delete(op_, obj);
+  }
+
+  modified_ = true;
+  counter_++;
+  Copy(op_, src, cur_);
+
+  StoreAtomic();
+  InvokeCallback();
+}
+
+// Sets the value of the flag based on specified string `value`. If the flag
+// was successfully set to new value, it returns true. Otherwise, sets `err`
+// to indicate the error, leaves the flag unchanged, and returns false. There
+// are three ways to set the flag's value:
+//  * Update the current flag value
+//  * Update the flag's default value
+//  * Update the current flag value if it was never set before
+// The mode is selected based on 'set_mode' parameter.
+bool FlagImpl::SetFromString(const CommandLineFlag& flag,
+                             absl::string_view value, FlagSettingMode set_mode,
+                             ValueSource source, std::string* err) {
+  absl::MutexLock l(DataGuard());
+
+  switch (set_mode) {
+    case SET_FLAGS_VALUE: {
+      // set or modify the flag's value
+      if (!TryParse(flag, cur_, value, err)) return false;
+      modified_ = true;
+      counter_++;
+      StoreAtomic();
+      InvokeCallback();
+
+      if (source == kCommandLine) {
+        on_command_line_ = true;
+      }
+      break;
+    }
+    case SET_FLAG_IF_DEFAULT: {
+      // set the flag's value, but only if it hasn't been set by someone else
+      if (!modified_) {
+        if (!TryParse(flag, cur_, value, err)) return false;
+        modified_ = true;
+        counter_++;
+        StoreAtomic();
+        InvokeCallback();
+      } else {
+        // TODO(rogeeff): review and fix this semantic. Currently we do not fail
+        // in this case if flag is modified. This is misleading since the flag's
+        // value is not updated even though we return true.
+        // *err = absl::StrCat(Name(), " is already set to ",
+        //                     CurrentValue(), "\n");
+        // return false;
+        return true;
+      }
+      break;
+    }
+    case SET_FLAGS_DEFAULT: {
+      // modify the flag's default-value
+      if (!TryParse(flag, def_, value, err)) return false;
+
+      if (!modified_) {
+        // Need to set both default value *and* current, in this case
+        Copy(op_, def_, cur_);
+        StoreAtomic();
+        InvokeCallback();
+      }
+      break;
+    }
+  }
+
+  return true;
+}
+
+void FlagImpl::CheckDefaultValueParsingRoundtrip(
+    const CommandLineFlag& flag) const {
+  std::string v = DefaultValue();
+
+  absl::MutexLock lock(DataGuard());
+
+  void* dst = Clone(op_, def_);
+  std::string error;
+  if (!flags_internal::Parse(marshalling_op_, v, dst, &error)) {
+    ABSL_INTERNAL_LOG(
+        FATAL,
+        absl::StrCat("Flag ", flag.Name(), " (from ", flag.Filename(),
+                     "): std::string form of default value '", v,
+                     "' could not be parsed; error=", error));
+  }
+
+  // We do not compare dst to def since parsing/unparsing may make
+  // small changes, e.g., precision loss for floating point types.
+  Delete(op_, dst);
+}
+
+bool FlagImpl::ValidateInputValue(absl::string_view value) const {
+  absl::MutexLock l(DataGuard());
+
+  void* obj = Clone(op_, def_);
+  std::string ignored_error;
+  const bool result =
+      flags_internal::Parse(marshalling_op_, value, obj, &ignored_error);
+  Delete(op_, obj);
+  return result;
 }
 
 }  // namespace flags_internal