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+//
+//  Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: usage_config.h
+// -----------------------------------------------------------------------------
+//
+// This file defines the main usage reporting configuration interfaces and
+// documents Abseil's supported built-in usage flags. If these flags are found
+// when parsing a command-line, Abseil will exit the program and display
+// appropriate help messages.
+#ifndef ABSL_FLAGS_USAGE_CONFIG_H_
+#define ABSL_FLAGS_USAGE_CONFIG_H_
+
+#include <functional>
+#include <string>
+
+#include "absl/strings/string_view.h"
+
+// -----------------------------------------------------------------------------
+// Built-in Usage Flags
+// -----------------------------------------------------------------------------
+//
+// Abseil supports the following built-in usage flags. When passed, these flags
+// exit the program and :
+//
+// * --help
+//     Shows help on important flags for this binary
+// * --helpfull
+//     Shows help on all flags
+// * --helpshort
+//     Shows help on only the main module for this program
+// * --helppackage
+//     Shows help on all modules in the main package
+// * --version
+//     Shows the version and build info for this binary and exits
+// * --only_check_args
+//     Exits after checking all flags
+// * --helpon
+//     Shows help on the modules named by this flag value
+// * --helpmatch
+//     Shows help on modules whose name contains the specified substring
+
+namespace absl {
+inline namespace lts_2019_08_08 {
+
+namespace flags_internal {
+using FlagKindFilter = std::function<bool (absl::string_view)>;
+}  // namespace flags_internal
+
+// FlagsUsageConfig
+//
+// This structure contains the collection of callbacks for changing the behavior
+// of the usage reporting routines in Abseil Flags.
+struct FlagsUsageConfig {
+  // Returns true if flags defined in the given source code file should be
+  // reported with --helpshort flag. For example, if the file
+  // "path/to/my/code.cc" defines the flag "--my_flag", and
+  // contains_helpshort_flags("path/to/my/code.cc") returns true, invoking the
+  // program with --helpshort will include information about --my_flag in the
+  // program output.
+  flags_internal::FlagKindFilter contains_helpshort_flags;
+
+  // Returns true if flags defined in the filename should be reported with
+  // --help flag. For example, if the file
+  // "path/to/my/code.cc" defines the flag "--my_flag", and
+  // contains_help_flags("path/to/my/code.cc") returns true, invoking the
+  // program with --help will include information about --my_flag in the
+  // program output.
+  flags_internal::FlagKindFilter contains_help_flags;
+
+  // Returns true if flags defined in the filename should be reported with
+  // --helppackage flag. For example, if the file
+  // "path/to/my/code.cc" defines the flag "--my_flag", and
+  // contains_helppackage_flags("path/to/my/code.cc") returns true, invoking the
+  // program with --helppackage will include information about --my_flag in the
+  // program output.
+  flags_internal::FlagKindFilter contains_helppackage_flags;
+
+  // Generates std::string containing program version. This is the std::string reported
+  // when user specifies --version in a command line.
+  std::function<std::string()> version_string;
+
+  // Normalizes the filename specific to the build system/filesystem used. This
+  // routine is used when we report the information about the flag definition
+  // location. For instance, if your build resides at some location you do not
+  // want to expose in the usage output, you can trim it to show only relevant
+  // part.
+  // For example:
+  //   normalize_filename("/my_company/some_long_path/src/project/file.cc")
+  // might produce
+  //   "project/file.cc".
+  std::function<std::string (absl::string_view)> normalize_filename;
+};
+
+// SetFlagsUsageConfig()
+//
+// Sets the usage reporting configuration callbacks. If any of the callbacks are
+// not set in usage_config instance, then the default value of the callback is
+// used.
+void SetFlagsUsageConfig(FlagsUsageConfig usage_config);
+
+namespace flags_internal {
+
+FlagsUsageConfig GetUsageConfig();
+
+void ReportUsageError(absl::string_view msg, bool is_fatal);
+
+}  // namespace flags_internal
+}  // inline namespace lts_2019_08_08
+}  // namespace absl
+
+extern "C" {
+
+// Additional report of fatal usage error message before we std::exit. Error is
+// fatal if is_fatal argument to ReportUsageError is true.
+void AbslInternalReportFatalUsageError(absl::string_view);
+
+}  // extern "C"
+
+#endif  // ABSL_FLAGS_USAGE_CONFIG_H_