NestedCommandLineApp Add -h as an alias for --help globally and to all subcommands

Summary: Alias `-h` to `--help` because we live in a society.

Reviewed By: yfeldblum

Differential Revision: D27370742

fbshipit-source-id: eb346546fe4066eef62313176ff7e47c20e507be

folly/experimental/NestedCommandLineApp.cpp

@@ -72,6 +72,7 @@ NestedCommandLineApp::NestedCommandLineApp(
         displayHelp(vm, args);
       });
   builtinCommands_.insert(kHelpCommand);
+  addAlias(kShortHelpCommand.str(), kHelpCommand.str());
 
   addCommand(
       kVersionCommand.str(),
@@ -84,7 +85,7 @@ NestedCommandLineApp::NestedCommandLineApp(
   builtinCommands_.insert(kVersionCommand);
 
   globalOptions_.add_options()(
-      kHelpCommand.str().c_str(),
+      (kHelpCommand.str() + "," + kShortHelpCommand.str()).c_str(),
       "Display help (globally or for a given command)")(
       kVersionCommand.str().c_str(), "Display version information");
 }

folly/experimental/NestedCommandLineApp.h

@@ -61,6 +61,7 @@ class NestedCommandLineApp {
       Command;
 
   static constexpr StringPiece const kHelpCommand = "help";
+  static constexpr StringPiece const kShortHelpCommand = "h";
   static constexpr StringPiece const kVersionCommand = "version";
   /**
    * Initialize the app.

folly/experimental/test/NestedCommandLineAppTest.cpp

@@ -75,6 +75,10 @@ TEST(ProgramOptionsTest, Errors) {
 TEST(ProgramOptionsTest, Help) {
   // Not actually checking help output, just verifying that help doesn't fail
   callHelper({"--version"});
+  callHelper({"--h"});
+  callHelper({"--h", "foo"});
+  callHelper({"--h", "bar"});
+  callHelper({"--h", "--", "bar"});
   callHelper({"--help"});
   callHelper({"--help", "foo"});
   callHelper({"--help", "bar"});
@@ -84,6 +88,7 @@ TEST(ProgramOptionsTest, Help) {
   callHelper({"help", "bar"});
 
   // wrong command name
+  callHelper({"-h", "qux"}, 1);
   callHelper({"--help", "qux"}, 1);
   callHelper({"help", "qux"}, 1);
 
@@ -93,6 +98,7 @@ TEST(ProgramOptionsTest, Help) {
 
 TEST(ProgramOptionsTest, DevFull) {
   folly::File full("/dev/full", O_RDWR);
+  callHelper({"-h"}, 1, full.fd());
   callHelper({"--help"}, 1, full.fd());
 }