summaryrefslogtreecommitdiff
path: root/absl/flags/parse.cc
blob: b60b36f60868ecb52ffa844a5977b0dfefb7292a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
//
// 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.

#include "absl/flags/parse.h"

#include <stdlib.h>

#include <algorithm>
#include <fstream>
#include <iostream>
#include <iterator>
#include <string>
#include <tuple>
#include <utility>
#include <vector>

#ifdef _WIN32
#include <windows.h>
#endif

#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/const_init.h"
#include "absl/base/thread_annotations.h"
#include "absl/flags/config.h"
#include "absl/flags/flag.h"
#include "absl/flags/internal/commandlineflag.h"
#include "absl/flags/internal/flag.h"
#include "absl/flags/internal/parse.h"
#include "absl/flags/internal/program_name.h"
#include "absl/flags/internal/registry.h"
#include "absl/flags/internal/usage.h"
#include "absl/flags/usage.h"
#include "absl/flags/usage_config.h"
#include "absl/strings/ascii.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/string_view.h"
#include "absl/strings/strip.h"
#include "absl/synchronization/mutex.h"

// --------------------------------------------------------------------

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace flags_internal {
namespace {

ABSL_CONST_INIT absl::Mutex processing_checks_guard(absl::kConstInit);

ABSL_CONST_INIT bool flagfile_needs_processing
    ABSL_GUARDED_BY(processing_checks_guard) = false;
ABSL_CONST_INIT bool fromenv_needs_processing
    ABSL_GUARDED_BY(processing_checks_guard) = false;
ABSL_CONST_INIT bool tryfromenv_needs_processing
    ABSL_GUARDED_BY(processing_checks_guard) = false;

}  // namespace
}  // namespace flags_internal
ABSL_NAMESPACE_END
}  // namespace absl

ABSL_FLAG(std::vector<std::string>, flagfile, {},
          "comma-separated list of files to load flags from")
    .OnUpdate([]() {
      if (absl::GetFlag(FLAGS_flagfile).empty()) return;

      absl::MutexLock l(&absl::flags_internal::processing_checks_guard);

      // Setting this flag twice before it is handled most likely an internal
      // error and should be reviewed by developers.
      if (absl::flags_internal::flagfile_needs_processing) {
        ABSL_INTERNAL_LOG(WARNING, "flagfile set twice before it is handled");
      }

      absl::flags_internal::flagfile_needs_processing = true;
    });
ABSL_FLAG(std::vector<std::string>, fromenv, {},
          "comma-separated list of flags to set from the environment"
          " [use 'export FLAGS_flag1=value']")
    .OnUpdate([]() {
      if (absl::GetFlag(FLAGS_fromenv).empty()) return;

      absl::MutexLock l(&absl::flags_internal::processing_checks_guard);

      // Setting this flag twice before it is handled most likely an internal
      // error and should be reviewed by developers.
      if (absl::flags_internal::fromenv_needs_processing) {
        ABSL_INTERNAL_LOG(WARNING, "fromenv set twice before it is handled.");
      }

      absl::flags_internal::fromenv_needs_processing = true;
    });
ABSL_FLAG(std::vector<std::string>, tryfromenv, {},
          "comma-separated list of flags to try to set from the environment if "
          "present")
    .OnUpdate([]() {
      if (absl::GetFlag(FLAGS_tryfromenv).empty()) return;

      absl::MutexLock l(&absl::flags_internal::processing_checks_guard);

      // Setting this flag twice before it is handled most likely an internal
      // error and should be reviewed by developers.
      if (absl::flags_internal::tryfromenv_needs_processing) {
        ABSL_INTERNAL_LOG(WARNING,
                          "tryfromenv set twice before it is handled.");
      }

      absl::flags_internal::tryfromenv_needs_processing = true;
    });

ABSL_FLAG(std::vector<std::string>, undefok, {},
          "comma-separated list of flag names that it is okay to specify "
          "on the command line even if the program does not define a flag "
          "with that name");

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace flags_internal {

namespace {

class ArgsList {
 public:
  ArgsList() : next_arg_(0) {}
  ArgsList(int argc, char* argv[]) : args_(argv, argv + argc), next_arg_(0) {}
  explicit ArgsList(const std::vector<std::string>& args)
      : args_(args), next_arg_(0) {}

  // Returns success status: true if parsing successful, false otherwise.
  bool ReadFromFlagfile(const std::string& flag_file_name);

  int Size() const { return args_.size() - next_arg_; }
  int FrontIndex() const { return next_arg_; }
  absl::string_view Front() const { return args_[next_arg_]; }
  void PopFront() { next_arg_++; }

 private:
  std::vector<std::string> args_;
  int next_arg_;
};

bool ArgsList::ReadFromFlagfile(const std::string& flag_file_name) {
  std::ifstream flag_file(flag_file_name);

  if (!flag_file) {
    flags_internal::ReportUsageError(
        absl::StrCat("Can't open flagfile ", flag_file_name), true);

    return false;
  }

  // This argument represents fake argv[0], which should be present in all arg
  // lists.
  args_.push_back("");

  std::string line;
  bool success = true;

  while (std::getline(flag_file, line)) {
    absl::string_view stripped = absl::StripLeadingAsciiWhitespace(line);

    if (stripped.empty() || stripped[0] == '#') {
      // Comment or empty line; just ignore.
      continue;
    }

    if (stripped[0] == '-') {
      if (stripped == "--") {
        flags_internal::ReportUsageError(
            "Flagfile can't contain position arguments or --", true);

        success = false;
        break;
      }

      args_.push_back(std::string(stripped));
      continue;
    }

    flags_internal::ReportUsageError(
        absl::StrCat("Unexpected line in the flagfile ", flag_file_name, ": ",
                     line),
        true);

    success = false;
  }

  return success;
}

// --------------------------------------------------------------------

// Reads the environment variable with name `name` and stores results in
// `value`. If variable is not present in environment returns false, otherwise
// returns true.
bool GetEnvVar(const char* var_name, std::string* var_value) {
#ifdef _WIN32
  char buf[1024];
  auto get_res = GetEnvironmentVariableA(var_name, buf, sizeof(buf));
  if (get_res >= sizeof(buf)) {
    return false;
  }

  if (get_res == 0) {
    return false;
  }

  *var_value = std::string(buf, get_res);
#else
  const char* val = ::getenv(var_name);
  if (val == nullptr) {
    return false;
  }

  *var_value = val;
#endif

  return true;
}

// --------------------------------------------------------------------

// Returns:
//  Flag name or empty if arg= --
//  Flag value after = in --flag=value (empty if --foo)
//  "Is empty value" status. True if arg= --foo=, false otherwise. This is
//  required to separate --foo from --foo=.
// For example:
//      arg           return values
//   "--foo=bar" -> {"foo", "bar", false}.
//   "--foo"     -> {"foo", "", false}.
//   "--foo="    -> {"foo", "", true}.
std::tuple<absl::string_view, absl::string_view, bool> SplitNameAndValue(
    absl::string_view arg) {
  // Allow -foo and --foo
  absl::ConsumePrefix(&arg, "-");

  if (arg.empty()) {
    return std::make_tuple("", "", false);
  }

  auto equal_sign_pos = arg.find("=");

  absl::string_view flag_name = arg.substr(0, equal_sign_pos);

  absl::string_view value;
  bool is_empty_value = false;

  if (equal_sign_pos != absl::string_view::npos) {
    value = arg.substr(equal_sign_pos + 1);
    is_empty_value = value.empty();
  }

  return std::make_tuple(flag_name, value, is_empty_value);
}

// --------------------------------------------------------------------

// Returns:
//  found flag or nullptr
//  is negative in case of --nofoo
std::tuple<CommandLineFlag*, bool> LocateFlag(absl::string_view flag_name) {
  CommandLineFlag* flag = flags_internal::FindCommandLineFlag(flag_name);
  bool is_negative = false;

  if (!flag && absl::ConsumePrefix(&flag_name, "no")) {
    flag = flags_internal::FindCommandLineFlag(flag_name);
    is_negative = true;
  }

  return std::make_tuple(flag, is_negative);
}

// --------------------------------------------------------------------

// Verify that default values of typed flags must be convertible to string and
// back.
void CheckDefaultValuesParsingRoundtrip() {
#ifndef NDEBUG
  flags_internal::ForEachFlag([&](CommandLineFlag* flag) {
    if (flag->IsRetired()) return;

#define IGNORE_TYPE(T) \
  if (flag->IsOfType<T>()) return;

    ABSL_FLAGS_INTERNAL_BUILTIN_TYPES(IGNORE_TYPE)
#undef IGNORE_TYPE

    flag->CheckDefaultValueParsingRoundtrip();
  });
#endif
}

// --------------------------------------------------------------------

// Returns success status, which is true if we successfully read all flag files,
// in which case new ArgLists are appended to the input_args in a reverse order
// of file names in the input flagfiles list. This order ensures that flags from
// the first flagfile in the input list are processed before the second flagfile
// etc.
bool ReadFlagfiles(const std::vector<std::string>& flagfiles,
                   std::vector<ArgsList>* input_args) {
  bool success = true;
  for (auto it = flagfiles.rbegin(); it != flagfiles.rend(); ++it) {
    ArgsList al;

    if (al.ReadFromFlagfile(*it)) {
      input_args->push_back(al);
    } else {
      success = false;
    }
  }

  return success;
}

// Returns success status, which is true if were able to locate all environment
// variables correctly or if fail_on_absent_in_env is false. The environment
// variable names are expected to be of the form `FLAGS_<flag_name>`, where
// `flag_name` is a string from the input flag_names list. If successful we
// append a single ArgList at the end of the input_args.
bool ReadFlagsFromEnv(const std::vector<std::string>& flag_names,
                      std::vector<ArgsList>* input_args,
                      bool fail_on_absent_in_env) {
  bool success = true;
  std::vector<std::string> args;

  // This argument represents fake argv[0], which should be present in all arg
  // lists.
  args.push_back("");

  for (const auto& flag_name : flag_names) {
    // Avoid infinite recursion.
    if (flag_name == "fromenv" || flag_name == "tryfromenv") {
      flags_internal::ReportUsageError(
          absl::StrCat("Infinite recursion on flag ", flag_name), true);

      success = false;
      continue;
    }

    const std::string envname = absl::StrCat("FLAGS_", flag_name);
    std::string envval;
    if (!GetEnvVar(envname.c_str(), &envval)) {
      if (fail_on_absent_in_env) {
        flags_internal::ReportUsageError(
            absl::StrCat(envname, " not found in environment"), true);

        success = false;
      }

      continue;
    }

    args.push_back(absl::StrCat("--", flag_name, "=", envval));
  }

  if (success) {
    input_args->emplace_back(args);
  }

  return success;
}

// --------------------------------------------------------------------

// Returns success status, which is true if were able to handle all generator
// flags (flagfile, fromenv, tryfromemv) successfully.
bool HandleGeneratorFlags(std::vector<ArgsList>* input_args,
                          std::vector<std::string>* flagfile_value) {
  bool success = true;

  absl::MutexLock l(&flags_internal::processing_checks_guard);

  // flagfile could have been set either on a command line or
  // programmatically before invoking ParseCommandLine. Note that we do not
  // actually process arguments specified in the flagfile, but instead
  // create a secondary arguments list to be processed along with the rest
  // of the comamnd line arguments. Since we always the process most recently
  // created list of arguments first, this will result in flagfile argument
  // being processed before any other argument in the command line. If
  // FLAGS_flagfile contains more than one file name we create multiple new
  // levels of arguments in a reverse order of file names. Thus we always
  // process arguments from first file before arguments containing in a
  // second file, etc. If flagfile contains another
  // --flagfile inside of it, it will produce new level of arguments and
  // processed before the rest of the flagfile. We are also collecting all
  // flagfiles set on original command line. Unlike the rest of the flags,
  // this flag can be set multiple times and is expected to be handled
  // multiple times. We are collecting them all into a single list and set
  // the value of FLAGS_flagfile to that value at the end of the parsing.
  if (flags_internal::flagfile_needs_processing) {
    auto flagfiles = absl::GetFlag(FLAGS_flagfile);

    if (input_args->size() == 1) {
      flagfile_value->insert(flagfile_value->end(), flagfiles.begin(),
                             flagfiles.end());
    }

    success &= ReadFlagfiles(flagfiles, input_args);

    flags_internal::flagfile_needs_processing = false;
  }

  // Similar to flagfile fromenv/tryfromemv can be set both
  // programmatically and at runtime on a command line. Unlike flagfile these
  // can't be recursive.
  if (flags_internal::fromenv_needs_processing) {
    auto flags_list = absl::GetFlag(FLAGS_fromenv);

    success &= ReadFlagsFromEnv(flags_list, input_args, true);

    flags_internal::fromenv_needs_processing = false;
  }

  if (flags_internal::tryfromenv_needs_processing) {
    auto flags_list = absl::GetFlag(FLAGS_tryfromenv);

    success &= ReadFlagsFromEnv(flags_list, input_args, false);

    flags_internal::tryfromenv_needs_processing = false;
  }

  return success;
}

// --------------------------------------------------------------------

void ResetGeneratorFlags(const std::vector<std::string>& flagfile_value) {
  // Setting flagfile to the value which collates all the values set on a
  // command line and programmatically. So if command line looked like
  // --flagfile=f1 --flagfile=f2 the final value of the FLAGS_flagfile flag is
  // going to be {"f1", "f2"}
  if (!flagfile_value.empty()) {
    absl::SetFlag(&FLAGS_flagfile, flagfile_value);
    absl::MutexLock l(&flags_internal::processing_checks_guard);
    flags_internal::flagfile_needs_processing = false;
  }

  // fromenv/tryfromenv are set to <undefined> value.
  if (!absl::GetFlag(FLAGS_fromenv).empty()) {
    absl::SetFlag(&FLAGS_fromenv, {});
  }
  if (!absl::GetFlag(FLAGS_tryfromenv).empty()) {
    absl::SetFlag(&FLAGS_tryfromenv, {});
  }

  absl::MutexLock l(&flags_internal::processing_checks_guard);
  flags_internal::fromenv_needs_processing = false;
  flags_internal::tryfromenv_needs_processing = false;
}

// --------------------------------------------------------------------

// Returns:
//  success status
//  deduced value
// We are also mutating curr_list in case if we need to get a hold of next
// argument in the input.
std::tuple<bool, absl::string_view> DeduceFlagValue(const CommandLineFlag& flag,
                                                    absl::string_view value,
                                                    bool is_negative,
                                                    bool is_empty_value,
                                                    ArgsList* curr_list) {
  // Value is either an argument suffix after `=` in "--foo=<value>"
  // or separate argument in case of "--foo" "<value>".

  // boolean flags have these forms:
  //   --foo
  //   --nofoo
  //   --foo=true
  //   --foo=false
  //   --nofoo=<value> is not supported
  //   --foo <value> is not supported

  // non boolean flags have these forms:
  // --foo=<value>
  // --foo <value>
  // --nofoo is not supported

  if (flag.IsOfType<bool>()) {
    if (value.empty()) {
      if (is_empty_value) {
        // "--bool_flag=" case
        flags_internal::ReportUsageError(
            absl::StrCat(
                "Missing the value after assignment for the boolean flag '",
                flag.Name(), "'"),
            true);
        return std::make_tuple(false, "");
      }

      // "--bool_flag" case
      value = is_negative ? "0" : "1";
    } else if (is_negative) {
      // "--nobool_flag=Y" case
      flags_internal::ReportUsageError(
          absl::StrCat("Negative form with assignment is not valid for the "
                       "boolean flag '",
                       flag.Name(), "'"),
          true);
      return std::make_tuple(false, "");
    }
  } else if (is_negative) {
    // "--noint_flag=1" case
    flags_internal::ReportUsageError(
        absl::StrCat("Negative form is not valid for the flag '", flag.Name(),
                     "'"),
        true);
    return std::make_tuple(false, "");
  } else if (value.empty() && (!is_empty_value)) {
    if (curr_list->Size() == 1) {
      // "--int_flag" case
      flags_internal::ReportUsageError(
          absl::StrCat("Missing the value for the flag '", flag.Name(), "'"),
          true);
      return std::make_tuple(false, "");
    }

    // "--int_flag" "10" case
    curr_list->PopFront();
    value = curr_list->Front();

    // Heuristic to detect the case where someone treats a string arg
    // like a bool or just forgets to pass a value:
    // --my_string_var --foo=bar
    // We look for a flag of string type, whose value begins with a
    // dash and corresponds to known flag or standalone --.
    if (!value.empty() && value[0] == '-' && flag.IsOfType<std::string>()) {
      auto maybe_flag_name = std::get<0>(SplitNameAndValue(value.substr(1)));

      if (maybe_flag_name.empty() ||
          std::get<0>(LocateFlag(maybe_flag_name)) != nullptr) {
        // "--string_flag" "--known_flag" case
        ABSL_INTERNAL_LOG(
            WARNING,
            absl::StrCat("Did you really mean to set flag '", flag.Name(),
                         "' to the value '", value, "'?"));
      }
    }
  }

  return std::make_tuple(true, value);
}

// --------------------------------------------------------------------

bool CanIgnoreUndefinedFlag(absl::string_view flag_name) {
  auto undefok = absl::GetFlag(FLAGS_undefok);
  if (std::find(undefok.begin(), undefok.end(), flag_name) != undefok.end()) {
    return true;
  }

  if (absl::ConsumePrefix(&flag_name, "no") &&
      std::find(undefok.begin(), undefok.end(), flag_name) != undefok.end()) {
    return true;
  }

  return false;
}

}  // namespace

// --------------------------------------------------------------------

std::vector<char*> ParseCommandLineImpl(int argc, char* argv[],
                                        ArgvListAction arg_list_act,
                                        UsageFlagsAction usage_flag_act,
                                        OnUndefinedFlag on_undef_flag) {
  ABSL_INTERNAL_CHECK(argc > 0, "Missing argv[0]");

  // This routine does not return anything since we abort on failure.
  CheckDefaultValuesParsingRoundtrip();

  std::vector<std::string> flagfile_value;

  std::vector<ArgsList> input_args;
  input_args.push_back(ArgsList(argc, argv));

  std::vector<char*> output_args;
  std::vector<char*> positional_args;
  output_args.reserve(argc);

  // This is the list of undefined flags. The element of the list is the pair
  // consisting of boolean indicating if flag came from command line (vs from
  // some flag file we've read) and flag name.
  // TODO(rogeeff): Eliminate the first element in the pair after cleanup.
  std::vector<std::pair<bool, std::string>> undefined_flag_names;

  // Set program invocation name if it is not set before.
  if (ProgramInvocationName() == "UNKNOWN") {
    flags_internal::SetProgramInvocationName(argv[0]);
  }
  output_args.push_back(argv[0]);

  // 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).
  bool success = true;
  while (!input_args.empty()) {
    // 10. First we process the built-in generator flags.
    success &= HandleGeneratorFlags(&input_args, &flagfile_value);

    // 30. Select top-most (most recent) arguments list. If it is empty drop it
    // and re-try.
    ArgsList& curr_list = input_args.back();

    curr_list.PopFront();

    if (curr_list.Size() == 0) {
      input_args.pop_back();
      continue;
    }

    // 40. Pick up the front remaining argument in the current list. If current
    // stack of argument lists contains only one element - we are processing an
    // argument from the original argv.
    absl::string_view arg(curr_list.Front());
    bool arg_from_argv = input_args.size() == 1;

    // 50. If argument does not start with - or is just "-" - this is
    // positional argument.
    if (!absl::ConsumePrefix(&arg, "-") || arg.empty()) {
      ABSL_INTERNAL_CHECK(arg_from_argv,
                          "Flagfile cannot contain positional argument");

      positional_args.push_back(argv[curr_list.FrontIndex()]);
      continue;
    }

    if (arg_from_argv && (arg_list_act == ArgvListAction::kKeepParsedArgs)) {
      output_args.push_back(argv[curr_list.FrontIndex()]);
    }

    // 60. Split the current argument on '=' to figure out the argument
    // name and value. If flag name is empty it means we've got "--". value
    // can be empty either if there were no '=' in argument string at all or
    // an argument looked like "--foo=". In a latter case is_empty_value is
    // true.
    absl::string_view flag_name;
    absl::string_view value;
    bool is_empty_value = false;

    std::tie(flag_name, value, is_empty_value) = SplitNameAndValue(arg);

    // 70. "--" alone means what it does for GNU: stop flags parsing. We do
    // not support positional arguments in flagfiles, so we just drop them.
    if (flag_name.empty()) {
      ABSL_INTERNAL_CHECK(arg_from_argv,
                          "Flagfile cannot contain positional argument");

      curr_list.PopFront();
      break;
    }

    // 80. Locate the flag based on flag name. Handle both --foo and --nofoo
    CommandLineFlag* flag = nullptr;
    bool is_negative = false;
    std::tie(flag, is_negative) = LocateFlag(flag_name);

    if (flag == nullptr) {
      if (on_undef_flag != OnUndefinedFlag::kIgnoreUndefined) {
        undefined_flag_names.emplace_back(arg_from_argv,
                                          std::string(flag_name));
      }
      continue;
    }

    // 90. Deduce flag's value (from this or next argument)
    auto curr_index = curr_list.FrontIndex();
    bool value_success = true;
    std::tie(value_success, value) =
        DeduceFlagValue(*flag, value, is_negative, is_empty_value, &curr_list);
    success &= value_success;

    // If above call consumed an argument, it was a standalone value
    if (arg_from_argv && (arg_list_act == ArgvListAction::kKeepParsedArgs) &&
        (curr_index != curr_list.FrontIndex())) {
      output_args.push_back(argv[curr_list.FrontIndex()]);
    }

    // 100. Set the located flag to a new new value, unless it is retired.
    // Setting retired flag fails, but we ignoring it here.
    if (flag->IsRetired()) continue;

    std::string error;
    if (!flag->ParseFrom(value, SET_FLAGS_VALUE, kCommandLine, &error)) {
      flags_internal::ReportUsageError(error, true);
      success = false;
    }
  }

  for (const auto& flag_name : undefined_flag_names) {
    if (CanIgnoreUndefinedFlag(flag_name.second)) continue;

    flags_internal::ReportUsageError(
        absl::StrCat("Unknown command line flag '", flag_name.second, "'"),
        true);

    success = false;
  }

#if ABSL_FLAGS_STRIP_NAMES
  if (!success) {
    flags_internal::ReportUsageError(
        "NOTE: command line flags are disabled in this build", true);
  }
#endif

  if (!success) {
    flags_internal::HandleUsageFlags(std::cout,
                                     ProgramUsageMessage());
    std::exit(1);
  }

  if (usage_flag_act == UsageFlagsAction::kHandleUsage) {
    int exit_code = flags_internal::HandleUsageFlags(
        std::cout, ProgramUsageMessage());

    if (exit_code != -1) {
      std::exit(exit_code);
    }
  }

  ResetGeneratorFlags(flagfile_value);

  // Reinstate positional args which were intermixed with flags in the arguments
  // list.
  for (auto arg : positional_args) {
    output_args.push_back(arg);
  }

  // All the remaining arguments are positional.
  if (!input_args.empty()) {
    for (int arg_index = input_args.back().FrontIndex(); arg_index < argc;
         ++arg_index) {
      output_args.push_back(argv[arg_index]);
    }
  }

  return output_args;
}

}  // namespace flags_internal

// --------------------------------------------------------------------

std::vector<char*> ParseCommandLine(int argc, char* argv[]) {
  return flags_internal::ParseCommandLineImpl(
      argc, argv, flags_internal::ArgvListAction::kRemoveParsedArgs,
      flags_internal::UsageFlagsAction::kHandleUsage,
      flags_internal::OnUndefinedFlag::kAbortIfUndefined);
}

ABSL_NAMESPACE_END
}  // namespace absl