Add more gn documentation

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"
 #include "tools/gn/err.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/input_conversion.h"
+#include "tools/gn/label.h"
 #include "tools/gn/label_pattern.h"
+#include "tools/gn/ninja_build_writer.h"
 #include "tools/gn/parser.h"
 #include "tools/gn/runtime_deps.h"
 #include "tools/gn/setup.h"
 #include "tools/gn/standard_out.h"
 #include "tools/gn/string_utils.h"
 #include "tools/gn/substitution_writer.h"
 #include "tools/gn/switches.h"
+#include "tools/gn/target.h"
 #include "tools/gn/variables.h"
 
 namespace commands {
 
 namespace {
 
 void PrintToplevelHelp() {
   OutputString("Commands (type \"gn help <command>\" for more details):\n");
   for (const auto& cmd : commands::GetCommands())
     PrintShortHelp(cmd.second.help_short);
@@ skipping 23 matching lines @@
   // 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("execution: Build graph and execution overview.");
   PrintShortHelp("grammar: Language and grammar for GN build files.");
   PrintShortHelp(
       "input_conversion: Processing input from exec_script and read_file.");
   PrintShortHelp("label_pattern: Matching more than one label.");
+  PrintShortHelp("labels: About labels.");
+  PrintShortHelp("ninja_rules: How Ninja build rules and named.");
   PrintShortHelp("nogncheck: Annotating includes for checking.");
   PrintShortHelp("runtime_deps: How runtime dependency computation works.");
   PrintShortHelp("source_expansion: Map sources to outputs for scripts.");
   PrintShortHelp("switches: Show available command-line switches.");
 }
 
 void PrintSwitchHelp() {
   const base::CommandLine* cmdline = base::CommandLine::ForCurrentProcess();
   bool use_markdown = cmdline->HasSwitch(switches::kMarkdown);
 
@@ skipping 38 matching lines @@
     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(kExecution_Help);
   PrintLongHelp(kGrammar_Help);
   PrintLongHelp(kInputConversion_Help);
   PrintLongHelp(kLabelPattern_Help);
+  PrintLongHelp(kLabels_Help);
+  PrintLongHelp(kNinjaRules_Help);
   PrintLongHelp(kNoGnCheck_Help);
   PrintLongHelp(kRuntimeDeps_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) {
@@ skipping 93 matching lines @@
   if (found_target_var != target_vars.end()) {
     PrintLongHelp(found_target_var->second.help);
     return 0;
   }
   for (const auto& entry : target_vars)
     all_help_topics.push_back(entry.first);
 
   // Random other topics.
   std::map<std::string, void(*)()> random_topics;
   random_topics["all"] = PrintAllHelp;
+  random_topics["execution"] = []() { PrintLongHelp(kExecution_Help); };
   random_topics["buildargs"] = []() { PrintLongHelp(kBuildArgs_Help); };
   random_topics["dotfile"] = []() { PrintLongHelp(kDotfile_Help); };
   random_topics["grammar"] = []() { PrintLongHelp(kGrammar_Help); };
   random_topics["input_conversion"] = []() {
     PrintLongHelp(kInputConversion_Help);
   };
   random_topics["label_pattern"] = []() { PrintLongHelp(kLabelPattern_Help); };
+  random_topics["labels"] = []() { PrintLongHelp(kLabels_Help); };
+  random_topics["ninja_rules"] = []() { PrintLongHelp(kNinjaRules_Help); };
   random_topics["nogncheck"] = []() { PrintLongHelp(kNoGnCheck_Help); };
   random_topics["runtime_deps"] = []() { PrintLongHelp(kRuntimeDeps_Help); };
   random_topics["source_expansion"] = []() {
     PrintLongHelp(kSourceExpansion_Help);
   };
   random_topics["switches"] = PrintSwitchHelp;
   auto found_random_topic = random_topics.find(what);
   if (found_random_topic != random_topics.end()) {
     found_random_topic->second();
     return 0;
   }
   for (const auto& entry : random_topics)
     all_help_topics.push_back(entry.first);
 
   // No help on this.
   Err(Location(), "No help on \"" + what + "\".").PrintToStdout();
   base::StringPiece suggestion = SpellcheckString(what, all_help_topics);
   if (suggestion.empty()) {
     OutputString("Run `gn help` for a list of available topics.\n",
                  DECORATION_NONE);
   } else {
     OutputString("Did you mean `gn help " + suggestion.as_string() + "`?\n",
                  DECORATION_NONE);
   }
   return 1;
 }
 
 }  // namespace commands