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[chromium-blink-merge.git] / third_party / cld / base / commandlineflags.h

// Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// This is the file that should be included by any file which declares
// or defines a command line flag or wants to parse command line flags
// or print a program usage message (which will include information about
// flags).  Executive summary, in the form of an example foo.cc file:
//
//    #include "foo.h"         // foo.h has a line "DECLARE_int32(start);"
//
//    DEFINE_int32(end, 1000, "The last record to read");
//    DECLARE_bool(verbose);   // some other file has a DEFINE_bool(verbose, ...)
//
//    void MyFunc() {
//      if (FLAGS_verbose) printf("Records %d-%d\n", FLAGS_start, FLAGS_end);
//    }
//
//    Then, at the command-line:
//       ./foo --noverbose --start=5 --end=100

#ifndef BASE_COMMANDLINEFLAGS_H_
#define BASE_COMMANDLINEFLAGS_H_

#include <assert.h>
#include <string>
#include <vector>
#include "base/basictypes.h"
#include "base/port.h"
#include "base/stl_decl_msvc.h"
#include "base/global_strip_options.h"

// --------------------------------------------------------------------
// To actually define a flag in a file, use DEFINE_bool,
// DEFINE_string, etc. at the bottom of this file.  You may also find
// it useful to register a validator with the flag.  This ensures that
// when the flag is parsed from the commandline, or is later set via
// SetCommandLineOption, we call the validation function.
//
// The validation function should return true if the flag value is valid, and
// false otherwise. If the function returns false for the new setting of the
// flag, the flag will retain its current value. If it returns false for the
// default value, InitGoogle will die.
//
// This function is safe to call at global construct time (as in the
// example below).
//
// Example use:
//    static bool ValidatePort(const char* flagname, int32 value) {
//       if (value > 0 && value < 32768)   // value is ok
//         return true;
//       printf("Invalid value for --%s: %d\n", flagname, (int)value);
//       return false;
//    }
//    DEFINE_int32(port, 0, "What port to listen on");
//    static bool dummy = RegisterFlagValidator(&FLAGS_port, &ValidatePort);

// Returns true if successfully registered, false if not (because the
// first argument doesn't point to a command-line flag, or because a
// validator is already registered for this flag).
bool RegisterFlagValidator(const bool* flag,
                           bool (*validate_fn)(const char*, bool));
bool RegisterFlagValidator(const int32* flag,
                           bool (*validate_fn)(const char*, int32));
bool RegisterFlagValidator(const int64* flag,
                           bool (*validate_fn)(const char*, int64));
bool RegisterFlagValidator(const uint64* flag,
                           bool (*validate_fn)(const char*, uint64));
bool RegisterFlagValidator(const double* flag,
                           bool (*validate_fn)(const char*, double));
bool RegisterFlagValidator(const string* flag,
                           bool (*validate_fn)(const char*, const string&));


// --------------------------------------------------------------------
// These methods are the best way to get access to info about the
// list of commandline flags.  Note that these routines are pretty slow.
//   GetAllFlags: mostly-complete info about the list, sorted by file.
//   ShowUsageWithFlags: pretty-prints the list to stdout (what --help does)
//   ShowUsageWithFlagsRestrict: limit to filenames with restrict as a substr
//
// In addition to accessing flags, you can also access argv[0] (the program
// name) and argv (the entire commandline), which we sock away a copy of.
// These variables are static, so you should only set them once.

struct CommandLineFlagInfo {
  string name;            // the name of the flag
  string type;            // the type of the flag: int32, etc
  string description;     // the "help text" associated with the flag
  string current_value;   // the current value, as a string
  string default_value;   // the default value, as a string
  string filename;        // 'cleaned' version of filename holding the flag
  bool is_default;        // true if the flag has default value
  bool has_validator_fn;  // true if RegisterFlagValidator called on this flag
};

extern void GetAllFlags(vector<CommandLineFlagInfo>* OUTPUT);
// These two are actually defined in commandlineflags_reporting.cc.
extern void ShowUsageWithFlags(const char *argv0);  // what --help does
extern void ShowUsageWithFlagsRestrict(const char *argv0, const char *restrict);

// Create a descriptive string for a flag.
// Goes to some trouble to make pretty line breaks.
extern string DescribeOneFlag(const CommandLineFlagInfo& flag);

// Thread-hostile; meant to be called before any threads are spawned.
extern void SetArgv(int argc, const char** argv);
// The following functions are thread-safe as long as SetArgv() is
// only called before any threads start.
extern const vector<string>& GetArgvs();    // all of argv = vector of strings
extern const char* GetArgv();               // all of argv as a string
extern const char* GetArgv0();              // only argv0
extern uint32 GetArgvSum();                 // simple checksum of argv
extern const char* ProgramInvocationName(); // argv0, or "UNKNOWN" if not set
extern const char* ProgramInvocationShortName();   // basename(argv0)
// ProgramUsage() is thread-safe as long as SetUsageMessage() is only
// called before any threads start.
extern const char* ProgramUsage();          // string set by SetUsageMessage()


// --------------------------------------------------------------------
// Normally you access commandline flags by just saying "if (FLAGS_foo)"
// or whatever, and set them by calling "FLAGS_foo = bar" (or, more
// commonly, via the DEFINE_foo macro).  But if you need a bit more
// control, we have programmatic ways to get/set the flags as well.
// These programmatic ways to access flags are thread-safe, but direct
// access is only thread-compatible.

// Return true iff the flagname was found.
// OUTPUT is set to the flag's value, or unchanged if we return false.
extern bool GetCommandLineOption(const char* name, string* OUTPUT);

// Return true iff the flagname was found. OUTPUT is set to the flag's
// CommandLineFlagInfo or unchanged if we return false.
extern bool GetCommandLineFlagInfo(const char* name,
                                   CommandLineFlagInfo* OUTPUT);

// Return the CommandLineFlagInfo of the flagname.  exit() if name not found.
// Example usage, to check if a flag's value is currently the default value:
//   if (GetCommandLineFlagInfoOrDie("foo").is_default) ...
extern CommandLineFlagInfo GetCommandLineFlagInfoOrDie(const char* name);

enum FlagSettingMode {
  // update the flag's value (can call this multiple times).
  SET_FLAGS_VALUE,
  // update the flag's value, but *only if* it has not yet been updated
  // with SET_FLAGS_VALUE, SET_FLAG_IF_DEFAULT, or "FLAGS_xxx = nondef".
  SET_FLAG_IF_DEFAULT,
  // set the flag's default value to this.  If the flag has not yet updated
  // yet (via SET_FLAGS_VALUE, SET_FLAG_IF_DEFAULT, or "FLAGS_xxx = nondef")
  // change the flag's current value to the new default value as well.
  SET_FLAGS_DEFAULT
};

// Set a particular flag ("command line option").  Returns a string
// describing the new value that the option has been set to.  The
// return value API is not well-specified, so basically just depend on
// it to be empty if the setting failed for some reason -- the name is
// not a valid flag name, or the value is not a valid value -- and
// non-empty else.

// SetCommandLineOption uses set_mode == SET_FLAGS_VALUE (the common case)
extern string SetCommandLineOption(const char* name, const char* value);
extern string SetCommandLineOptionWithMode(const char* name, const char* value,
                                           FlagSettingMode set_mode);


// --------------------------------------------------------------------
// Saves the states (value, default value, whether the user has set
// the flag, registered validators, etc) of all flags, and restores
// them when the FlagSaver is destroyed.  This is very useful in
// tests, say, when you want to let your tests change the flags, but
// make sure that they get reverted to the original states when your
// test is complete.
//
// Example usage:
//   void TestFoo() {
//     FlagSaver s1;
//     FLAG_foo = false;
//     FLAG_bar = "some value";
//
//     // test happens here.  You can return at any time
//     // without worrying about restoring the FLAG values.
//   }
//
// Note: This class is marked with ATTRIBUTE_UNUSED because all the
// work is done in the constructor and destructor, so in the standard
// usage example above, the compiler would complain that it's an
// unused variable.
//
// This class is thread-safe.
/*
class FlagSaver {
 public:
  FlagSaver();
  ~FlagSaver();

 private:
  class FlagSaverImpl* impl_;   // we use pimpl here to keep API steady

  FlagSaver(const FlagSaver&);  // no copying!
  void operator=(const FlagSaver&);
}
#ifndef SWIG   // swig seems to have trouble with this for some reason
ATTRIBUTE_UNUSED
#endif
;
*/
// --------------------------------------------------------------------
// Some deprecated or hopefully-soon-to-be-deprecated functions.

// This is often used for logging.  TODO(csilvers): figure out a better way
extern string CommandlineFlagsIntoString();
// Usually where this is used, a FlagSaver should be used instead.
extern bool ReadFlagsFromString(const string& flagfilecontents,
                                const char* prog_name,
                                bool errors_are_fatal); // uses SET_FLAGS_VALUE

// These let you manually implement --flagfile functionality.
// DEPRECATED.
extern bool AppendFlagsIntoFile(const string& filename, const char* prog_name);
extern bool SaveCommandFlags();  // actually defined in google.cc !
extern bool ReadFromFlagsFile(const string& filename, const char* prog_name,
                              bool errors_are_fatal);   // uses SET_FLAGS_VALUE


// --------------------------------------------------------------------
// Useful routines for initializing flags from the environment.
// In each case, if 'varname' does not exist in the environment
// return defval.  If 'varname' does exist but is not valid
// (e.g., not a number for an int32 flag), abort with an error.
// Otherwise, return the value.  NOTE: for booleans, for true use
// 't' or 'T' or 'true' or '1', for false 'f' or 'F' or 'false' or '0'.

extern bool BoolFromEnv(const char *varname, bool defval);
extern int32 Int32FromEnv(const char *varname, int32 defval);
extern int64 Int64FromEnv(const char *varname, int64 defval);
extern uint64 Uint64FromEnv(const char *varname, uint64 defval);
extern double DoubleFromEnv(const char *varname, double defval);
extern const char *StringFromEnv(const char *varname, const char *defval);


// --------------------------------------------------------------------
// The next two functions parse commandlineflags from main():

// Set the "usage" message for this program.  For example:
//   string usage("This program does nothing.  Sample usage:\n");
//   usage += argv[0] + " <uselessarg1> <uselessarg2>";
//   SetUsageMessage(usage);
// Do not include commandline flags in the usage: we do that for you!
// Thread-hostile; meant to be called before any threads are spawned.
extern void SetUsageMessage(const string& usage);

// Looks for flags in argv and parses them.  Rearranges argv to put
// flags first, or removes them entirely if remove_flags is true.
// If a flag is defined more than once in the command line or flag
// file, the last definition is used.
// See top-of-file for more details on this function.
#ifndef SWIG   // In swig, use ParseCommandLineFlagsScript() instead.
extern uint32 ParseCommandLineFlags(int *argc, char*** argv,
                                    bool remove_flags);
#endif


// Calls to ParseCommandLineNonHelpFlags and then to
// HandleCommandLineHelpFlags can be used instead of a call to
// ParseCommandLineFlags during initialization, in order to allow for
// changing default values for some FLAGS (via
// e.g. SetCommandLineOptionWithMode calls) between the time of
// command line parsing and the time of dumping help information for
// the flags as a result of command line parsing.
// If a flag is defined more than once in the command line or flag
// file, the last definition is used.
extern uint32 ParseCommandLineNonHelpFlags(int *argc, char*** argv,
                                           bool remove_flags);
// This is actually defined in commandlineflags_reporting.cc.
// This function is misnamed (it also handles --version, etc.), but
// it's too late to change that now. :-(
extern void HandleCommandLineHelpFlags();   // in commandlineflags_reporting.cc

// Allow command line reparsing.  Disables the error normally
// generated when an unknown flag is found, since it may be found in a
// later parse.  Thread-hostile; meant to be called before any threads
// are spawned.
extern void AllowCommandLineReparsing();

// Reparse the flags that have not yet been recognized.
// Only flags registered since the last parse will be recognized.
// Any flag value must be provided as part of the argument using "=",
// not as a separate command line argument that follows the flag argument.
// Intended for handling flags from dynamically loaded libraries,
// since their flags are not registered until they are loaded.
extern uint32 ReparseCommandLineNonHelpFlags();


// --------------------------------------------------------------------
// Now come the command line flag declaration/definition macros that
// will actually be used.  They're kind of hairy.  A major reason
// for this is initialization: we want people to be able to access
// variables in global constructors and have that not crash, even if
// their global constructor runs before the global constructor here.
// (Obviously, we can't guarantee the flags will have the correct
// default value in that case, but at least accessing them is safe.)
// The only way to do that is have flags point to a static buffer.
// So we make one, using a union to ensure proper alignment, and
// then use placement-new to actually set up the flag with the
// correct default value.  In the same vein, we have to worry about
// flag access in global destructors, so FlagRegisterer has to be
// careful never to destroy the flag-values it constructs.
//
// Note that when we define a flag variable FLAGS_<name>, we also
// preemptively define a junk variable, FLAGS_no<name>.  This is to
// cause a link-time error if someone tries to define 2 flags with
// names like "logging" and "nologging".  We do this because a bool
// flag FLAG can be set from the command line to true with a "-FLAG"
// argument, and to false with a "-noFLAG" argument, and so this can
// potentially avert confusion.
//
// We also put flags into their own namespace.  It is purposefully
// named in an opaque way that people should have trouble typing
// directly.  The idea is that DEFINE puts the flag in the weird
// namespace, and DECLARE imports the flag from there into the current
// namespace.  The net result is to force people to use DECLARE to get
// access to a flag, rather than saying "extern bool FLAGS_whatever;"
// or some such instead.  We want this so we can put extra
// functionality (like sanity-checking) in DECLARE if we want, and
// make sure it is picked up everywhere.
//
// We also put the type of the variable in the namespace, so that
// people can't DECLARE_int32 something that they DEFINE_bool'd
// elsewhere.

class FlagRegisterer {
 public:
  FlagRegisterer(const char* name, const char* type,
                 const char* help, const char* filename,
                 void* current_storage, void* defvalue_storage);
};

#ifndef SWIG  // In swig, ignore the main flag declarations

// If STRIP_FLAG_HELP is defined and is non-zero, we remove the help
// message from the binary file. This is useful for security reasons
// when shipping a binary outside of Google (if the user cannot see
// the usage message by executing the program, they shouldn't be able
// to see it by running "strings binary_file").

extern const char kStrippedFlagHelp[];

#if STRIP_FLAG_HELP > 0
// Need this construct to avoid the 'defined but not used' warning.
#define MAYBE_STRIPPED_HELP(txt) (false ? (txt) : kStrippedFlagHelp)
#else
#define MAYBE_STRIPPED_HELP(txt) txt
#endif

// Each command-line flag has two variables associated with it: one
// with the current value, and one with the default value.  However,
// we have a third variable, which is where value is assigned; it's a
// constant.  This guarantees that FLAG_##value is initialized at
// static initialization time (e.g. before program-start) rather than
// than global construction time (which is after program-start but
// before main), at least when 'value' is a compile-time constant.  We
// use a small trick for the "default value" variable, and call it
// FLAGS_no<name>.  This serves the second purpose of assuring a
// compile error if someone tries to define a flag named no<name>
// which is illegal (--foo and --nofoo both affect the "foo" flag).
#define DEFINE_VARIABLE(type, shorttype, name, value, help) \
  namespace fL##shorttype {                                     \
    static const type FLAGS_nono##name = value;                 \
    type FLAGS_##name = FLAGS_nono##name;                       \
    type FLAGS_no##name = FLAGS_nono##name;                     \
    static FlagRegisterer o_##name(                             \
      #name, #type, MAYBE_STRIPPED_HELP(help), __FILE__,        \
      &FLAGS_##name, &FLAGS_no##name);                          \
  }                                                             \
  using fL##shorttype::FLAGS_##name

#define DECLARE_VARIABLE(type, shorttype, name) \
  namespace fL##shorttype {                     \
    extern type FLAGS_##name;                   \
  }                                             \
  using fL##shorttype::FLAGS_##name

// For boolean flags, we want to do the extra check that the passed-in
// value is actually a bool, and not a string or something that can be
// coerced to a bool.  These declarations (no definition needed!) will
// help us do that, and never evaluate from, which is important.
// We'll use 'sizeof(IsBool(val))' to distinguish.
namespace fLB {
template<typename From> double IsBoolFlag(const From& from);
bool IsBoolFlag(bool from);
}
extern bool FlagsTypeWarn(const char *name);

#define DECLARE_bool(name)          DECLARE_VARIABLE(bool,B, name)
// We have extra code here to make sure 'val' is actually a boolean.
#define DEFINE_bool(name,val,txt)   namespace fLB { \
                                      const bool FLAGS_nonono##name = \
                                        (sizeof(::fLB::IsBoolFlag(val)) \
                                        == sizeof(double)) \
                                        ? FlagsTypeWarn(#name) : true; \
                                    } \
                                    DEFINE_VARIABLE(bool,B, name, val, txt)
#define DECLARE_int32(name)         DECLARE_VARIABLE(int32,I, name)
#define DEFINE_int32(name,val,txt)  DEFINE_VARIABLE(int32,I, name, val, txt)

#define DECLARE_int64(name)         DECLARE_VARIABLE(int64,I64, name)
#define DEFINE_int64(name,val,txt)  DEFINE_VARIABLE(int64,I64, name, val, txt)

#define DECLARE_uint64(name)        DECLARE_VARIABLE(uint64,U64, name)
#define DEFINE_uint64(name,val,txt) DEFINE_VARIABLE(uint64,U64, name, val, txt)

#define DECLARE_double(name)        DECLARE_VARIABLE(double,D, name)
#define DEFINE_double(name,val,txt) DEFINE_VARIABLE(double,D, name, val, txt)

// Strings are trickier, because they're not a POD, so we can't
// construct them at static-initialization time (instead they get
// constructed at global-constructor time, which is much later).  To
// try to avoid crashes in that case, we use a char buffer to store
// the string, which we can static-initialize, and then placement-new
// into it later.  It's not perfect, but the best we can do.
#define DECLARE_string(name)  namespace fLS { extern string& FLAGS_##name; } \
                              using fLS::FLAGS_##name

// We need to define a var named FLAGS_no##name so people don't define
// --string and --nostring.  And we need a temporary place to put val
// so we don't have to evaluate it twice.  Two great needs that go
// great together!
#define DEFINE_string(name, val, txt)                                     \
  namespace fLS {                                                         \
    static union { void* align; char s[sizeof(string)]; } s_##name[2];    \
    const string* const FLAGS_no##name = new (s_##name[0].s) string(val); \
    static FlagRegisterer o_##name(                                       \
      #name, "string", MAYBE_STRIPPED_HELP(txt), __FILE__,                \
      s_##name[0].s, new (s_##name[1].s) string(*FLAGS_no##name));        \
    string& FLAGS_##name = *(reinterpret_cast<string*>(s_##name[0].s));   \
  }                                                                       \
  using fLS::FLAGS_##name

#endif  // SWIG

#endif  // BASE_COMMANDLINEFLAGS_H_