4 files changed, 119 insertions, 14 deletions
diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h
index f53f484f8f44..b060199e12b0 100644
--- a/absl/flags/internal/flag.h
+++ b/absl/flags/internal/flag.h
@@ -40,6 +40,30 @@
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
+
+// Forward declaration of absl::Flag<T> public API.
+namespace flags_internal {
+template <typename T>
+class Flag;
+}  // namespace flags_internal
+
+#if defined(_MSC_VER) && !defined(__clang__)
+template <typename T>
+class Flag;
+#else
+template <typename T>
+using Flag = flags_internal::Flag<T>;
+#endif
+
+template <typename T>
+ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag);
+
+template <typename T>
+void SetFlag(absl::Flag<T>* flag, const T& v);
+
+template <typename T, typename V>
+void SetFlag(absl::Flag<T>* flag, const V& v);
+
 namespace flags_internal {
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -596,6 +620,32 @@ class Flag {
               flags_internal::StorageKind<T>(), default_arg),
         value_() {}
 
+  // CommandLineFlag interface
+  absl::string_view Name() const { return impl_.Name(); }
+  std::string Filename() const { return impl_.Filename(); }
+  std::string Help() const { return impl_.Help(); }
+  bool IsSpecifiedOnCommandLine() const {
+    return impl_.IsSpecifiedOnCommandLine();
+  }
+  std::string DefaultValue() const { return impl_.DefaultValue(); }
+  std::string CurrentValue() const { return impl_.CurrentValue(); }
+
+ private:
+  template <typename U, bool do_register>
+  friend class FlagRegistrar;
+
+#if !defined(_MSC_VER) || defined(__clang__)
+  template <typename U>
+  friend U absl::GetFlag(const flags_internal::Flag<U>& flag);
+  template <typename U>
+  friend void absl::SetFlag(flags_internal::Flag<U>* flag, const U& v);
+  template <typename U, typename V>
+  friend void absl::SetFlag(flags_internal::Flag<U>* flag, const V& v);
+#else
+  template <typename U>
+  friend class absl::Flag;
+#endif
+
   T Get() const {
     // See implementation notes in CommandLineFlag::Get().
     union U {
@@ -617,20 +667,6 @@ class Flag {
     impl_.Write(&v);
   }
 
-  // CommandLineFlag interface
-  absl::string_view Name() const { return impl_.Name(); }
-  std::string Filename() const { return impl_.Filename(); }
-  std::string Help() const { return impl_.Help(); }
-  bool IsSpecifiedOnCommandLine() const {
-    return impl_.IsSpecifiedOnCommandLine();
-  }
-  std::string DefaultValue() const { return impl_.DefaultValue(); }
-  std::string CurrentValue() const { return impl_.CurrentValue(); }
-
- private:
-  template <typename U, bool do_register>
-  friend class FlagRegistrar;
-
   // Flag's data
   // The implementation depends on value_ field to be placed exactly after the
   // impl_ field, so that impl_ can figure out the offset to the value and
diff --git a/absl/flags/internal/parse.h b/absl/flags/internal/parse.h
index 03e8a07bf3ab..d259be733ce2 100644
--- a/absl/flags/internal/parse.h
+++ b/absl/flags/internal/parse.h
@@ -44,6 +44,13 @@ std::vector<char*> ParseCommandLineImpl(int argc, char* argv[],
                                         UsageFlagsAction usage_flag_act,
                                         OnUndefinedFlag on_undef_flag);
 
+// --------------------------------------------------------------------
+// Inspect original command line
+
+// Returns true if flag with specified name was either present on the original
+// command line or specified in flag file present on the original command line.
+bool WasPresentOnCommandLine(absl::string_view flag_name);
+
 }  // namespace flags_internal
 ABSL_NAMESPACE_END
 }  // namespace absl
diff --git a/absl/flags/parse.cc b/absl/flags/parse.cc
index 66a28a93c7f7..2e8f03b4bb5d 100644
--- a/absl/flags/parse.cc
+++ b/absl/flags/parse.cc
@@ -67,6 +67,22 @@ ABSL_CONST_INIT bool fromenv_needs_processing
 ABSL_CONST_INIT bool tryfromenv_needs_processing
     ABSL_GUARDED_BY(processing_checks_guard) = false;
 
+ABSL_CONST_INIT absl::Mutex specified_flags_guard(absl::kConstInit);
+ABSL_CONST_INIT std::vector<const CommandLineFlag*>* specified_flags
+    ABSL_GUARDED_BY(specified_flags_guard) = nullptr;
+
+struct SpecifiedFlagsCompare {
+  bool operator()(const CommandLineFlag* a, const CommandLineFlag* b) const {
+    return a->Name() < b->Name();
+  }
+  bool operator()(const CommandLineFlag* a, absl::string_view b) const {
+    return a->Name() < b;
+  }
+  bool operator()(absl::string_view a, const CommandLineFlag* b) const {
+    return a < b->Name();
+  }
+};
+
 }  // namespace
 }  // namespace flags_internal
 ABSL_NAMESPACE_END
@@ -577,6 +593,17 @@ bool CanIgnoreUndefinedFlag(absl::string_view flag_name) {
 
 // --------------------------------------------------------------------
 
+bool WasPresentOnCommandLine(absl::string_view flag_name) {
+  absl::MutexLock l(&specified_flags_guard);
+  ABSL_INTERNAL_CHECK(specified_flags != nullptr,
+                      "ParseCommandLine is not invoked yet");
+
+  return std::binary_search(specified_flags->begin(), specified_flags->end(),
+                            flag_name, SpecifiedFlagsCompare{});
+}
+
+// --------------------------------------------------------------------
+
 std::vector<char*> ParseCommandLineImpl(int argc, char* argv[],
                                         ArgvListAction arg_list_act,
                                         UsageFlagsAction usage_flag_act,
@@ -607,6 +634,13 @@ std::vector<char*> ParseCommandLineImpl(int argc, char* argv[],
   }
   output_args.push_back(argv[0]);
 
+  absl::MutexLock l(&specified_flags_guard);
+  if (specified_flags == nullptr) {
+    specified_flags = new std::vector<const CommandLineFlag*>;
+  } else {
+    specified_flags->clear();
+  }
+
   // Iterate through the list of the input arguments. First level are arguments
   // originated from argc/argv. Following levels are arguments originated from
   // recursive parsing of flagfile(s).
@@ -702,6 +736,8 @@ std::vector<char*> ParseCommandLineImpl(int argc, char* argv[],
             flag, value, SET_FLAGS_VALUE, kCommandLine, &error)) {
       flags_internal::ReportUsageError(error, true);
       success = false;
+    } else {
+      specified_flags->push_back(flag);
     }
   }
 
@@ -753,6 +789,10 @@ std::vector<char*> ParseCommandLineImpl(int argc, char* argv[],
     }
   }
 
+  // Trim and sort the vector.
+  specified_flags->shrink_to_fit();
+  std::sort(specified_flags->begin(), specified_flags->end(),
+            SpecifiedFlagsCompare{});
   return output_args;
 }
 
diff --git a/absl/flags/parse_test.cc b/absl/flags/parse_test.cc
index 065f757a6c9e..e6a53ae6cb43 100644
--- a/absl/flags/parse_test.cc
+++ b/absl/flags/parse_test.cc
@@ -869,4 +869,26 @@ TEST_F(ParseDeathTest, TestHelpFlagHandling) {
   EXPECT_EQ(absl::GetFlag(FLAGS_int_flag), 3);
 }
 
+// --------------------------------------------------------------------
+
+TEST_F(ParseTest, WasPresentOnCommandLine) {
+  const char* in_args1[] = {
+      "testbin",        "arg1", "--bool_flag",
+      "--int_flag=211", "arg2", "--double_flag=1.1",
+      "--string_flag",  "asd",  "--",
+      "--some_flag",    "arg4",
+  };
+
+  InvokeParse(in_args1);
+
+  EXPECT_TRUE(flags::WasPresentOnCommandLine("bool_flag"));
+  EXPECT_TRUE(flags::WasPresentOnCommandLine("int_flag"));
+  EXPECT_TRUE(flags::WasPresentOnCommandLine("double_flag"));
+  EXPECT_TRUE(flags::WasPresentOnCommandLine("string_flag"));
+  EXPECT_FALSE(flags::WasPresentOnCommandLine("some_flag"));
+  EXPECT_FALSE(flags::WasPresentOnCommandLine("another_flag"));
+}
+
+// --------------------------------------------------------------------
+
 }  // namespace