Enhance GN's "desc" command to support configs.

tools/gn/command_ls.cc

 // Copyright 2014 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 <set>
 
 #include "base/command_line.h"
 #include "tools/gn/commands.h"
 #include "tools/gn/label_pattern.h"
 #include "tools/gn/setup.h"
 #include "tools/gn/standard_out.h"
+#include "tools/gn/switches.h"
 #include "tools/gn/target.h"
 
 namespace commands {
 
 const char kLs[] = "ls";
 const char kLs_HelpShort[] =
     "ls: List matching targets.";
 const char kLs_Help[] =
     "gn ls <out_dir> [<label_pattern>] [--all-toolchains] [--as=...]\n"
     "      [--type=...] [--testonly=...]\n"
     "\n"
     "  Lists all targets matching the given pattern for the given build\n"
     "  directory. By default, only targets in the default toolchain will\n"
     "  be matched unless a toolchain is explicitly supplied.\n"
     "\n"
     "  If the label pattern is unspecified, list all targets. The label\n"
     "  pattern is not a general regular expression (see\n"
     "  \"gn help label_pattern\"). If you need more complex expressions,\n"
     "  pipe the result through grep.\n"
     "\n"
     "Options\n"
     "\n"
     TARGET_PRINTING_MODE_COMMAND_LINE_HELP
     "\n"
-    "  --all-toolchains\n"
-    "      Matches all toolchains. When set, if the label pattern does not\n"
-    "      specify an explicit toolchain, labels from all toolchains will be\n"
-    "      matched. When unset, only targets in the default toolchain will\n"
-    "      be matched unless an explicit toolchain in the label is set.\n"
+    ALL_TOOLCHAINS_SWITCH_HELP
     "\n"
     TARGET_TESTONLY_FILTER_COMMAND_LINE_HELP
     "\n"
     TARGET_TYPE_FILTER_COMMAND_LINE_HELP
     "\n"
     "Examples\n"
     "\n"
     "  gn ls out/Debug\n"
     "      Lists all targets in the default toolchain.\n"
     "\n"
@@ skipping 22 matching lines @@
         "Usage: \"gn ls <build dir> [<label_pattern>]*\"").PrintToStdout();
     return 1;
   }
 
   Setup* setup = new Setup;
   setup->build_settings().set_check_for_bad_items(false);
   if (!setup->DoSetup(args[0], false) || !setup->Run())
     return 1;
 
   const base::CommandLine* cmdline = base::CommandLine::ForCurrentProcess();
-  bool all_toolchains = cmdline->HasSwitch("all-toolchains");
+  bool all_toolchains = cmdline->HasSwitch(switches::kAllToolchains);
 
   std::vector<const Target*> matches;
   if (args.size() > 1) {
     // Some patterns or explicit labels were specified.
     std::vector<std::string> inputs(args.begin() + 1, args.end());
 
     UniqueVector<const Target*> target_matches;
     UniqueVector<const Config*> config_matches;
     UniqueVector<const Toolchain*> toolchain_matches;
     UniqueVector<SourceFile> file_matches;
@@ skipping 11 matching lines @@
     for (const auto& target : setup->builder()->GetAllResolvedTargets()) {
       if (target->settings()->is_default())
         matches.push_back(target);
     }
   }
   FilterAndPrintTargets(false, &matches);
   return 0;
 }
 
 }  // namespace commands