WTF NPAPI extension. Early draft.

tools/nixysa/third_party/gflags-1.0/src/gflags_completions.cc

+// Copyright (c) 2008, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// ---
+// Author: Dave Nicponski
+//
+// Bash-style command line flag completion for C++ binaries
+//
+// This module implements bash-style completions.  It achieves this
+// goal in the following broad chunks:
+//
+//  1) Take a to-be-completed word, and examine it for search hints
+//  2) Identify all potentially matching flags
+//     2a) If there are no matching flags, do nothing.
+//     2b) If all matching flags share a common prefix longer than the
+//         completion word, output just that matching prefix
+//  3) Categorize those flags to produce a rough ordering of relevence.
+//  4) Potentially trim the set of flags returned to a smaller number
+//     that bash is happier with
+//  5) Output the matching flags in groups ordered by relevence.
+//     5a) Force bash to place most-relevent groups at the top of the list
+//     5b) Trim most flag's descriptions to fit on a single terminal line
+
+
+#include "config.h"
+#include <stdlib.h>
+
+#include <set>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "gflags/gflags.h"
+
+using std::set;
+using std::string;
+using std::vector;
+
+#ifndef PATH_SEPARATOR
+#define PATH_SEPARATOR  '/'
+#endif
+
+DEFINE_string(tab_completion_word, "",
+              "If non-empty, HandleCommandLineCompletions() will hijack the "
+              "process and attempt to do bash-style command line flag "
+              "completion on this value.");
+DEFINE_int32(tab_completion_columns, 80,
+             "Number of columns to use in output for tab completion");
+
+_START_GOOGLE_NAMESPACE_
+
+namespace {
+
+// Function prototypes and Type forward declarations.  Code may be
+// more easily understood if it is roughly ordered according to
+// control flow, rather than by C's "declare before use" ordering
+struct CompletionOptions;
+struct NotableFlags;
+
+// The entry point if flag completion is to be used.
+static void PrintFlagCompletionInfo(void);
+
+
+// 1) Examine search word
+static void CanonicalizeCursorWordAndSearchOptions(
+    const string &cursor_word,
+    string *canonical_search_token,
+    CompletionOptions *options);
+
+static bool RemoveTrailingChar(string *str, char c);
+
+
+// 2) Find all matches
+static void FindMatchingFlags(
+    const vector<CommandLineFlagInfo> &all_flags,
+    const CompletionOptions &options,
+    const string &match_token,
+    set<const CommandLineFlagInfo *> *all_matches,
+    string *longest_common_prefix);
+
+static bool DoesSingleFlagMatch(
+    const CommandLineFlagInfo &flag,
+    const CompletionOptions &options,
+    const string &match_token);
+
+
+// 3) Categorize matches
+static void CategorizeAllMatchingFlags(
+    const set<const CommandLineFlagInfo *> &all_matches,
+    const string &search_token,
+    const string &module,
+    const string &package_dir,
+    NotableFlags *notable_flags);
+
+static void TryFindModuleAndPackageDir(
+    const vector<CommandLineFlagInfo> all_flags,
+    string *module,
+    string *package_dir);
+
+
+// 4) Decide which flags to use
+static void FinalizeCompletionOutput(
+    const set<const CommandLineFlagInfo *> &matching_flags,
+    CompletionOptions *options,
+    NotableFlags *notable_flags,
+    vector<string> *completions);
+
+static void RetrieveUnusedFlags(
+    const set<const CommandLineFlagInfo *> &matching_flags,
+    const NotableFlags &notable_flags,
+    set<const CommandLineFlagInfo *> *unused_flags);
+
+
+// 5) Output matches
+static void OutputSingleGroupWithLimit(
+    const set<const CommandLineFlagInfo *> &group,
+    const string &line_indentation,
+    const string &header,
+    const string &footer,
+    bool long_output_format,
+    int *remaining_line_limit,
+    size_t *completion_elements_added,
+    vector<string> *completions);
+
+// (helpers for #5)
+static string GetShortFlagLine(
+    const string &line_indentation,
+    const CommandLineFlagInfo &info);
+
+static string GetLongFlagLine(
+    const string &line_indentation,
+    const CommandLineFlagInfo &info);
+
+
+//
+// Useful types
+
+// Try to deduce the intentions behind this completion attempt.  Return the
+// canonical search term in 'canonical_search_token'.  Binary search options
+// are returned in the various booleans, which should all have intuitive
+// semantics, possibly except:
+//  - return_all_matching_flags: Generally, we'll trim the number of
+//    returned candidates to some small number, showing those that are
+//    most likely to be useful first.  If this is set, however, the user
+//    really does want us to return every single flag as an option.
+//  - force_no_update: Any time we output lines, all of which share a
+//    common prefix, bash will 'helpfully' not even bother to show the
+//    output, instead changing the current word to be that common prefix.
+//    If it's clear this shouldn't happen, we'll set this boolean
+struct CompletionOptions {
+  bool flag_name_substring_search;
+  bool flag_location_substring_search;
+  bool flag_description_substring_search;
+  bool return_all_matching_flags;
+  bool force_no_update;
+};
+
+// Notable flags are flags that are special or preferred for some
+// reason.  For example, flags that are defined in the binary's module
+// are expected to be much more relevent than flags defined in some
+// other random location.  These sets are specified roughly in precedence
+// order.  Once a flag is placed in one of these 'higher' sets, it won't
+// be placed in any of the 'lower' sets.
+struct NotableFlags {
+  typedef set<const CommandLineFlagInfo *> FlagSet;
+  FlagSet perfect_match_flag;
+  FlagSet module_flags;       // Found in module file
+  FlagSet package_flags;      // Found in same directory as module file
+  FlagSet most_common_flags;  // One of the XXX most commonly supplied flags
+  FlagSet subpackage_flags;   // Found in subdirectories of package
+};
+
+
+//
+// Tab completion implementation - entry point
+static void PrintFlagCompletionInfo(void) {
+  string cursor_word = FLAGS_tab_completion_word;
+  string canonical_token;
+  CompletionOptions options = { };
+  CanonicalizeCursorWordAndSearchOptions(
+      cursor_word,
+      &canonical_token,
+      &options);
+
+  //VLOG(1) << "Identified canonical_token: '" << canonical_token << "'";
+
+  vector<CommandLineFlagInfo> all_flags;
+  set<const CommandLineFlagInfo *> matching_flags;
+  GetAllFlags(&all_flags);
+  //VLOG(2) << "Found " << all_flags.size() << " flags overall";
+
+  string longest_common_prefix;
+  FindMatchingFlags(
+      all_flags,
+      options,
+      canonical_token,
+      &matching_flags,
+      &longest_common_prefix);
+  //VLOG(1) << "Identified " << matching_flags.size() << " matching flags";
+  //VLOG(1) << "Identified " << longest_common_prefix
+  //        << " as longest common prefix.";
+  if (longest_common_prefix.size() > canonical_token.size()) {
+    // There's actually a shared common prefix to all matching flags,
+    // so may as well output that and quit quickly.
+    //VLOG(1) << "The common prefix '" << longest_common_prefix
+    //        << "' was longer than the token '" << canonical_token
+    //        << "'.  Returning just this prefix for completion.";
+    fprintf(stdout, "--%s", longest_common_prefix.c_str());
+    return;
+  }
+  if (matching_flags.empty()) {
+    //VLOG(1) << "There were no matching flags, returning nothing.";
+    return;
+  }
+
+  string module;
+  string package_dir;
+  TryFindModuleAndPackageDir(all_flags, &module, &package_dir);
+  //VLOG(1) << "Identified module: '" << module << "'";
+  //VLOG(1) << "Identified package_dir: '" << package_dir << "'";
+
+  NotableFlags notable_flags;
+  CategorizeAllMatchingFlags(
+      matching_flags,
+      canonical_token,
+      module,
+      package_dir,
+      &notable_flags);
+  //VLOG(2) << "Categorized matching flags:";
+  //VLOG(2) << " perfect_match: " << notable_flags.perfect_match_flag.size();
+  //VLOG(2) << " module: " << notable_flags.module_flags.size();
+  //VLOG(2) << " package: " << notable_flags.package_flags.size();
+  //VLOG(2) << " most common: " << notable_flags.most_common_flags.size();
+  //VLOG(2) << " subpackage: " << notable_flags.subpackage_flags.size();
+
+  vector<string> completions;
+  FinalizeCompletionOutput(
+      matching_flags,
+      &options,
+      &notable_flags,
+      &completions);
+
+  if (options.force_no_update)
+    completions.push_back("~");
+
+  //VLOG(1) << "Finalized with " << completions.size()
+  //        << " chosen completions";
+
+  for (vector<string>::const_iterator it = completions.begin();
+      it != completions.end();
+      ++it) {
+    //VLOG(9) << "  Completion entry: '" << *it << "'";
+    fprintf(stdout, "%s\n", it->c_str());
+  }
+}
+
+
+// 1) Examine search word (and helper method)
+static void CanonicalizeCursorWordAndSearchOptions(
+    const string &cursor_word,
+    string *canonical_search_token,
+    CompletionOptions *options) {
+  *canonical_search_token = cursor_word;
+  if (canonical_search_token->empty()) return;
+
+  // Get rid of leading quotes and dashes in the search term
+  if ((*canonical_search_token)[0] == '"')
+    *canonical_search_token = canonical_search_token->substr(1);
+  while ((*canonical_search_token)[0] == '-')
+    *canonical_search_token = canonical_search_token->substr(1);
+
+  options->flag_name_substring_search = false;
+  options->flag_location_substring_search = false;
+  options->flag_description_substring_search = false;
+  options->return_all_matching_flags = false;
+  options->force_no_update = false;
+
+  // Look for all search options we can deduce now.  Do this by walking
+  // backwards through the term, looking for up to three '?' and up to
+  // one '+' as suffixed characters.  Consume them if found, and remove
+  // them from the canonical search token.
+  int found_question_marks = 0;
+  int found_plusses = 0;
+  while (true) {
+    if (found_question_marks < 3 &&
+        RemoveTrailingChar(canonical_search_token, '?')) {
+      ++found_question_marks;
+      continue;
+    }
+    if (found_plusses < 1 &&
+        RemoveTrailingChar(canonical_search_token, '+')) {
+      ++found_plusses;
+      continue;
+    }
+    break;
+  }
+
+  switch (found_question_marks) {  // all fallthroughs
+    case 3: options->flag_description_substring_search = true;
+    case 2: options->flag_location_substring_search = true;
+    case 1: options->flag_name_substring_search = true;
+  };
+
+  options->return_all_matching_flags = (found_plusses > 0);
+}
+
+// Returns true if a char was removed
+static bool RemoveTrailingChar(string *str, char c) {
+  if (str->empty()) return false;
+  if ((*str)[str->size() - 1] == c) {
+    *str = str->substr(0, str->size() - 1);
+    return true;
+  }
+  return false;
+}
+
+
+// 2) Find all matches (and helper methods)
+static void FindMatchingFlags(
+    const vector<CommandLineFlagInfo> &all_flags,
+    const CompletionOptions &options,
+    const string &match_token,
+    set<const CommandLineFlagInfo *> *all_matches,
+    string *longest_common_prefix) {
+  all_matches->clear();
+  bool first_match = true;
+  for (vector<CommandLineFlagInfo>::const_iterator it = all_flags.begin();
+      it != all_flags.end();
+      ++it) {
+    if (DoesSingleFlagMatch(*it, options, match_token)) {
+      all_matches->insert(&*it);
+      if (first_match) {
+        first_match = false;
+        *longest_common_prefix = it->name;
+      } else {
+        if (longest_common_prefix->empty() || it->name.empty()) {
+          longest_common_prefix->clear();
+          continue;
+        }
+        string::size_type pos = 0;
+        while (pos < longest_common_prefix->size() &&
+            pos < it->name.size() &&
+            (*longest_common_prefix)[pos] == it->name[pos])
+          ++pos;
+        longest_common_prefix->erase(pos);
+      }
+    }
+  }
+}
+
+// Given the set of all flags, the parsed match options, and the
+// canonical search token, produce the set of all candidate matching
+// flags for subsequent analysis or filtering.
+static bool DoesSingleFlagMatch(
+    const CommandLineFlagInfo &flag,
+    const CompletionOptions &options,
+    const string &match_token) {
+  // Is there a prefix match?
+  string::size_type pos = flag.name.find(match_token);
+  if (pos == 0) return true;
+
+  // Is there a substring match if we want it?
+  if (options.flag_name_substring_search &&
+      pos != string::npos)
+    return true;
+
+  // Is there a location match if we want it?
+  if (options.flag_location_substring_search &&
+      flag.filename.find(match_token) != string::npos)
+    return true;
+
+  // TODO(daven): All searches should probably be case-insensitive
+  // (especially this one...)
+  if (options.flag_description_substring_search &&
+      flag.description.find(match_token) != string::npos)
+    return true;
+
+  return false;
+}
+
+// 3) Categorize matches (and helper method)
+
+// Given a set of matching flags, categorize them by
+// likely relevence to this specific binary
+static void CategorizeAllMatchingFlags(
+    const set<const CommandLineFlagInfo *> &all_matches,
+    const string &search_token,
+    const string &module,  // empty if we couldn't find any
+    const string &package_dir,  // empty if we couldn't find any
+    NotableFlags *notable_flags) {
+  notable_flags->perfect_match_flag.clear();
+  notable_flags->module_flags.clear();
+  notable_flags->package_flags.clear();
+  notable_flags->most_common_flags.clear();
+  notable_flags->subpackage_flags.clear();
+
+  for (set<const CommandLineFlagInfo *>::const_iterator it =
+        all_matches.begin();
+      it != all_matches.end();
+      ++it) {
+    //VLOG(2) << "Examining match '" << (*it)->name << "'";
+    //VLOG(7) << "  filename: '" << (*it)->filename << "'";
+    string::size_type pos = string::npos;
+    if (!package_dir.empty())
+      pos = (*it)->filename.find(package_dir);
+    string::size_type slash = string::npos;
+    if (pos != string::npos)  // candidate for package or subpackage match
+      slash = (*it)->filename.find(
+          PATH_SEPARATOR,
+          pos + package_dir.size() + 1);
+
+    if ((*it)->name == search_token) {
+      // Exact match on some flag's name
+      notable_flags->perfect_match_flag.insert(*it);
+      //VLOG(3) << "Result: perfect match";
+    } else if (!module.empty() && (*it)->filename == module) {
+      // Exact match on module filename
+      notable_flags->module_flags.insert(*it);
+      //VLOG(3) << "Result: module match";
+    } else if (!package_dir.empty() &&
+        pos != string::npos && slash == string::npos) {
+      // In the package, since there was no slash after the package portion
+      notable_flags->package_flags.insert(*it);
+      //VLOG(3) << "Result: package match";
+    } else if (false) {
+      // In the list of the XXX most commonly supplied flags overall
+      // TODO(daven): Compile this list.
+      //VLOG(3) << "Result: most-common match";
+    } else if (!package_dir.empty() &&
+        pos != string::npos && slash != string::npos) {
+      // In a subdirectory of the package
+      notable_flags->subpackage_flags.insert(*it);
+      //VLOG(3) << "Result: subpackage match";
+    }
+
+    //VLOG(3) << "Result: not special match";
+  }
+}
+
+static void TryFindModuleAndPackageDir(
+    const vector<CommandLineFlagInfo> all_flags,
+    string *module,
+    string *package_dir) {
+  module->clear();
+  package_dir->clear();
+
+  vector<string> suffixes;
+  // TODO(daven): There's some inherant ambiguity here - multiple directories
+  // could share the same trailing folder and file structure (and even worse,
+  // same file names), causing us to be unsure as to which of the two is the
+  // actual package for this binary.  In this case, we'll arbitrarily choose.
+  string progname(ProgramInvocationShortName());
+  suffixes.push_back("/" + progname + ".");
+  suffixes.push_back("/" + progname + "-main.");
+  suffixes.push_back("/" + progname + "_main.");
+  // These four are new but probably merited?
+  suffixes.push_back("/" + progname + "_test.");
+  suffixes.push_back("/" + progname + "-test.");
+  suffixes.push_back("/" + progname + "_unittest.");
+  suffixes.push_back("/" + progname + "-unittest.");
+
+  for (vector<CommandLineFlagInfo>::const_iterator it = all_flags.begin();
+      it != all_flags.end();
+      ++it) {
+    for (vector<string>::const_iterator suffix = suffixes.begin();
+        suffix != suffixes.end();
+        ++suffix) {
+      // TODO(daven): Make sure the match is near the end of the string
+      if (it->filename.find(*suffix) != string::npos) {
+        *module = it->filename;
+        string::size_type sep = it->filename.rfind(PATH_SEPARATOR);
+        *package_dir = it->filename.substr(0, (sep == string::npos) ? 0 : sep);
+        return;
+      }
+    }
+  }
+}
+
+// Can't specialize template type on a locally defined type.  Silly C++...
+struct DisplayInfoGroup {
+  string header;
+  string footer;
+  set<const CommandLineFlagInfo *> *group;
+
+  int SizeInLines() const {
+    int size_in_lines = static_cast<int>(group->size()) + 1;
+    if (!header.empty()) {
+      size_in_lines++;
+    }
+    if (!footer.empty()) {
+      size_in_lines++;
+    }
+    return size_in_lines;
+  }
+};
+
+// 4) Finalize and trim output flag set
+static void FinalizeCompletionOutput(
+    const set<const CommandLineFlagInfo *> &matching_flags,
+    CompletionOptions *options,
+    NotableFlags *notable_flags,
+    vector<string> *completions) {
+
+  // We want to output lines in groups.  Each group needs to be indented
+  // the same to keep its lines together.  Unless otherwise required,
+  // only 99 lines should be output to prevent bash from harassing the
+  // user.
+
+  // First, figure out which output groups we'll actually use.  For each
+  // nonempty group, there will be ~3 lines of header & footer, plus all
+  // output lines themselves.
+  int max_desired_lines =  // "999999 flags should be enough for anyone.  -dave"
+    (options->return_all_matching_flags ? 999999 : 98);
+  int lines_so_far = 0;
+
+  vector<DisplayInfoGroup> output_groups;
+  bool perfect_match_found = false;
+  if (lines_so_far < max_desired_lines &&
+      !notable_flags->perfect_match_flag.empty()) {
+    perfect_match_found = true;
+    DisplayInfoGroup group =
+        { string(),
+          "==========",
+          &notable_flags->perfect_match_flag };
+    lines_so_far += group.SizeInLines();
+    output_groups.push_back(group);
+  }
+  if (lines_so_far < max_desired_lines &&
+      !notable_flags->module_flags.empty()) {
+    DisplayInfoGroup group = {
+        "-* Matching module flags *-",
+        "===========================",
+        &notable_flags->module_flags };
+    lines_so_far += group.SizeInLines();
+    output_groups.push_back(group);
+  }
+  if (lines_so_far < max_desired_lines &&
+      !notable_flags->package_flags.empty()) {
+    DisplayInfoGroup group = {
+        "-* Matching package flags *-",
+        "============================",
+        &notable_flags->package_flags };
+    lines_so_far += group.SizeInLines();
+    output_groups.push_back(group);
+  }
+  if (lines_so_far < max_desired_lines &&
+      !notable_flags->most_common_flags.empty()) {
+    DisplayInfoGroup group = {
+        "-* Commonly used flags *-",
+        "=========================",
+        &notable_flags->most_common_flags };
+    lines_so_far += group.SizeInLines();
+    output_groups.push_back(group);
+  }
+  if (lines_so_far < max_desired_lines &&
+      !notable_flags->subpackage_flags.empty()) {
+    DisplayInfoGroup group = {
+        "-* Matching sub-package flags *-",
+        "================================",
+        &notable_flags->subpackage_flags };
+    lines_so_far += group.SizeInLines();
+    output_groups.push_back(group);
+  }
+
+  set<const CommandLineFlagInfo *> obscure_flags;  // flags not notable
+  if (lines_so_far < max_desired_lines) {
+    RetrieveUnusedFlags(matching_flags, *notable_flags, &obscure_flags);
+    if (!obscure_flags.empty()) {
+      DisplayInfoGroup group = {
+          "-* Other flags *-",
+          string(),
+          &obscure_flags };
+      lines_so_far += group.SizeInLines();
+      output_groups.push_back(group);
+    }
+  }
+
+  // Second, go through each of the chosen output groups and output
+  // as many of those flags as we can, while remaining below our limit
+  int remaining_lines = max_desired_lines;
+  size_t completions_output = 0;
+  int indent = static_cast<int>(output_groups.size()) - 1;
+  for (vector<DisplayInfoGroup>::const_iterator it =
+        output_groups.begin();
+      it != output_groups.end();
+      ++it, --indent) {
+    OutputSingleGroupWithLimit(
+        *it->group,  // group
+        string(indent, ' '),  // line indentation
+        it->header,  // header
+        it->footer,  // footer
+        perfect_match_found,  // long format
+        &remaining_lines,  // line limit - reduces this by number printed
+        &completions_output,  // completions (not lines) added
+        completions);  // produced completions
+    perfect_match_found = false;
+  }
+
+  if (completions_output != matching_flags.size()) {
+    options->force_no_update = false;
+    completions->push_back("~ (Remaining flags hidden) ~");
+  } else {
+    options->force_no_update = true;
+  }
+}
+
+static void RetrieveUnusedFlags(
+    const set<const CommandLineFlagInfo *> &matching_flags,
+    const NotableFlags &notable_flags,
+    set<const CommandLineFlagInfo *> *unused_flags) {
+  // Remove from 'matching_flags' set all members of the sets of
+  // flags we've already printed (specifically, those in notable_flags)
+  for (set<const CommandLineFlagInfo *>::const_iterator it =
+        matching_flags.begin();
+      it != matching_flags.end();
+      ++it) {
+    if (notable_flags.perfect_match_flag.count(*it) ||
+        notable_flags.module_flags.count(*it) ||
+        notable_flags.package_flags.count(*it) ||
+        notable_flags.most_common_flags.count(*it) ||
+        notable_flags.subpackage_flags.count(*it))
+      continue;
+    unused_flags->insert(*it);
+  }
+}
+
+// 5) Output matches (and helpfer methods)
+
+static void OutputSingleGroupWithLimit(
+    const set<const CommandLineFlagInfo *> &group,
+    const string &line_indentation,
+    const string &header,
+    const string &footer,
+    bool long_output_format,
+    int *remaining_line_limit,
+    size_t *completion_elements_output,
+    vector<string> *completions) {
+  if (group.empty()) return;
+  if (!header.empty()) {
+    if (*remaining_line_limit < 2) return;
+    *remaining_line_limit -= 2;
+    completions->push_back(line_indentation + header);
+    completions->push_back(line_indentation + string(header.size(), '-'));
+  }
+  for (set<const CommandLineFlagInfo *>::const_iterator it = group.begin();
+      it != group.end() && *remaining_line_limit > 0;
+      ++it) {
+    --*remaining_line_limit;
+    ++*completion_elements_output;
+    completions->push_back(
+        (long_output_format
+          ? GetLongFlagLine(line_indentation, **it)
+          : GetShortFlagLine(line_indentation, **it)));
+  }
+  if (!footer.empty()) {
+    if (*remaining_line_limit < 1) return;
+    --*remaining_line_limit;
+    completions->push_back(line_indentation + footer);
+  }
+}
+
+static string GetShortFlagLine(
+    const string &line_indentation,
+    const CommandLineFlagInfo &info) {
+  string prefix =
+    line_indentation + "--" + info.name + " [" +
+    (info.type == "string" ?
+       ("'" + info.default_value + "'") :
+       info.default_value)
+    + "] ";
+  int remainder =
+      FLAGS_tab_completion_columns - static_cast<int>(prefix.size());
+  string suffix;
+  if (remainder > 0)
+    suffix =
+        (static_cast<int>(info.description.size()) > remainder ?
+         (info.description.substr(0, remainder - 3) + "...").c_str() :
+         info.description.c_str());
+  return prefix + suffix;
+}
+
+static string GetLongFlagLine(
+    const string &line_indentation,
+    const CommandLineFlagInfo &info) {
+
+  string output = DescribeOneFlag(info);
+
+  // Replace '-' with '--', and remove trailing newline before appending
+  // the module definition location.
+  string old_flagname = "-" + info.name;
+  output.replace(
+      output.find(old_flagname),
+      old_flagname.size(),
+      "-" + old_flagname);
+  // Stick a newline and indentation in front of the type and default
+  // portions of DescribeOneFlag()s description
+  static const char kNewlineWithIndent[] = "\n    ";
+  output.replace(output.find(" type:"), 1, string(kNewlineWithIndent));
+  output.replace(output.find(" default:"), 1, string(kNewlineWithIndent));
+  output = line_indentation + " Details for '--" + info.name + "':\n" +
+     output + "    defined: " + info.filename;
+
+  // Eliminate any doubled newlines that crept in.  Specifically, if
+  // DescribeOneFlag() decided to break the line just before "type"
+  // or "default", we don't want to introduce an extra blank line
+  static const string line_of_spaces(FLAGS_tab_completion_columns, ' ');
+  static const char kDoubledNewlines[] = "\n     \n";
+  for (string::size_type newlines = output.find(kDoubledNewlines);
+      newlines != string::npos;
+      newlines = output.find(kDoubledNewlines))
+    // Replace each 'doubled newline' with a single newline
+    output.replace(newlines, sizeof(kDoubledNewlines) - 1, string("\n"));
+
+  for (string::size_type newline = output.find('\n');
+      newline != string::npos;
+      newline = output.find('\n')) {
+    int newline_pos = static_cast<int>(newline) % FLAGS_tab_completion_columns;
+    int missing_spaces = FLAGS_tab_completion_columns - newline_pos;
+    output.replace(newline, 1, line_of_spaces, 1, missing_spaces);
+  }
+  return output;
+}
+}  // anonymous
+
+void HandleCommandLineCompletions(void) {
+  if (FLAGS_tab_completion_word.empty()) return;
+  PrintFlagCompletionInfo();
+  exit(0);
+}
+
+_END_GOOGLE_NAMESPACE_