Add a "gn help all" option to GN to print all of the help at once.

tools/gn/command_help.cc

 // Copyright (c) 2013 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.
 
 #include <algorithm>
 #include <iostream>
 
 #include "base/command_line.h"
 #include "tools/gn/args.h"
 #include "tools/gn/commands.h"
@@ skipping 39 matching lines @@
   for (const auto& builtin : variables::GetBuiltinVariables())
     PrintShortHelp(builtin.second.help_short);
 
   // Target variables.
   OutputString("\nVariables you set in targets (type \"gn help <variable>\" "
                "for more details):\n");
   for (const auto& target : variables::GetTargetVariables())
     PrintShortHelp(target.second.help_short);
 
   OutputString("\nOther help topics:\n");
+  PrintShortHelp("all: Print all the help at once");
   PrintShortHelp("buildargs: How build arguments work.");
   PrintShortHelp("dotfile: Info about the toplevel .gn file.");
   PrintShortHelp("grammar: Formal grammar for GN build files.");
   PrintShortHelp("label_pattern: Matching more than one label.");
   PrintShortHelp(
       "input_conversion: Processing input from exec_script and read_file.");
   PrintShortHelp("source_expansion: Map sources to outputs for scripts.");
   PrintShortHelp("switches: Show available command-line switches.");
 }
 
 void PrintSwitchHelp() {
   OutputString("Available global switches\n", DECORATION_YELLOW);
   OutputString(
       "  Do \"gn help --the_switch_you_want_help_on\" for more. Individual\n"
       "  commands may take command-specific switches not listed here. See the\n"
       "  help on your specific command for more.\n\n");
 
   for (const auto& s : switches::GetSwitches())
     PrintShortHelp(s.second.short_help);
 }
 
+void PrintAllHelp() {
+  PrintToplevelHelp();
+
+  for (const auto& s : switches::GetSwitches())
+    PrintLongHelp(s.second.long_help);
+
+  for (const auto& c: commands::GetCommands())
+    PrintLongHelp(c.second.help);
+
+  for (const auto& f: functions::GetFunctions())
+    PrintLongHelp(f.second.help);
+
+  for (const auto& v: variables::GetBuiltinVariables())
+    PrintLongHelp(v.second.help);
+
+  for (const auto& v: variables::GetTargetVariables())
+    PrintLongHelp(v.second.help);
+
+  PrintLongHelp(kBuildArgs_Help);
+  PrintLongHelp(kDotfile_Help);
+  PrintLongHelp(kInputConversion_Help);
+  PrintLongHelp(kLabelPattern_Help);
+  PrintLongHelp(kSourceExpansion_Help);
+  PrintSwitchHelp();
+}
+
 // Prints help on the given switch. There should be no leading hyphens. Returns
 // true if the switch was found and help was printed. False means the switch is
 // unknown.
 bool PrintHelpOnSwitch(const std::string& what) {
   const switches::SwitchInfoMap& all = switches::GetSwitches();
   switches::SwitchInfoMap::const_iterator found =
       all.find(base::StringPiece(what));
   if (found == all.end())
     return false;
   PrintLongHelp(found->second.long_help);
@@ skipping 65 matching lines @@
   const variables::VariableInfoMap& target_vars =
       variables::GetTargetVariables();
   variables::VariableInfoMap::const_iterator found_target_var =
       target_vars.find(what);
   if (found_target_var != target_vars.end()) {
     PrintLongHelp(found_target_var->second.help);
     return 0;
   }
 
   // Random other topics.
+  if (what == "all") {
+    PrintAllHelp();
+    return 0;
+  }
   if (what == "buildargs") {
     PrintLongHelp(kBuildArgs_Help);
     return 0;
   }
   if (what == "dotfile") {
     PrintLongHelp(kDotfile_Help);
     return 0;
   }
   if (what == "grammar") {
     PrintLongHelp(kGrammar_Help);
@@ skipping 16 matching lines @@
     return 0;
   }
 
   // No help on this.
   Err(Location(), "No help on \"" + what + "\".").PrintToStdout();
   RunHelp(std::vector<std::string>());
   return 1;
 }
 
 }  // namespace commands