Add a move-focus subcommand (microsoft#8546)

## Summary of the Pull Request

Adds support for the `move-focus` subcommand to `wt.exe`. This subcommand works _exactly_ like `moveFocus(up|down|left|right)`. 

## References
* Will surely conflict with microsoft#8183
* Is goodness even in the world where microsoft#5464 exists

## PR Checklist
* [x] Closes microsoft#6580 
* [x] I work here
* [x] Tests added/passed
* [x] Docs PR: MicrosoftDocs/terminal#209

## Detailed Description of the Pull Request / Additional comments

Bear with me, I wrote this before paternity leave, so code might be a bit stale.

Oddly, after startup, this _does not_ leave the focus on the pane you moved to. If you `move-focus` during startup, at the end of startup, we'll still focus a _random_ pane. This is because the terminal still auto-focus a TermControl when it's done with layout. While we'll maintain the active control just fine during the startup, at the end of startup, all the controls will complete layout in a random order. 

This is no different than the startup right now. `wt sp ; sp ; sp` will focus a random pane at the end. This is left for a future someone to fix

This is also subject to microsoft#2398 / microsoft#4692. Moving in a direction isn't _totally_ reliable currently. `focus-pane -t ID` will certainly be more reliable, but this will work in the meantime?

## Validation Steps Performed

Opened probably 100 terminals, confirmed that the layout was always correct. Final focused pane was random, but the layout was right.

src/cascadia/LocalTests_TerminalApp/CommandlineTest.cpp

@@ -47,6 +47,7 @@ namespace TerminalAppLocalTests
         TEST_METHOD(ParseSplitPaneIntoArgs);
         TEST_METHOD(ParseComboCommandlineIntoArgs);
         TEST_METHOD(ParseFocusTabArgs);
+        TEST_METHOD(ParseMoveFocusArgs);
         TEST_METHOD(ParseArgumentsWithParsingTerminators);
 
         TEST_METHOD(ParseNoCommandIsNewTab);
@@ -76,6 +77,23 @@ namespace TerminalAppLocalTests
             appArgs.ValidateStartupCommands();
         }
 
+        void _buildCommandlinesExpectFailureHelper(AppCommandlineArgs& appArgs,
+                                                   const size_t expectedSubcommands,
+                                                   std::vector<const wchar_t*>& rawCommands)
+        {
+            auto commandlines = AppCommandlineArgs::BuildCommands(rawCommands);
+            VERIFY_ARE_EQUAL(expectedSubcommands, commandlines.size());
+            for (auto& cmdBlob : commandlines)
+            {
+                const auto result = appArgs.ParseCommand(cmdBlob);
+                VERIFY_ARE_NOT_EQUAL(0, result);
+                VERIFY_ARE_NOT_EQUAL("", appArgs._exitMessage);
+                Log::Comment(NoThrowString().Format(
+                    L"Exit Message:\n%hs",
+                    appArgs._exitMessage.c_str()));
+            }
+        }
+
         void _logCommandline(std::vector<const wchar_t*>& rawCommands)
         {
             std::wstring buffer;
@@ -995,6 +1013,124 @@ namespace TerminalAppLocalTests
         }
     }
 
+    void CommandlineTest::ParseMoveFocusArgs()
+    {
+        BEGIN_TEST_METHOD_PROPERTIES()
+            TEST_METHOD_PROPERTY(L"Data:useShortForm", L"{false, true}")
+        END_TEST_METHOD_PROPERTIES()
+
+        INIT_TEST_PROPERTY(bool, useShortForm, L"If true, use `mf` instead of `move-focus`");
+        const wchar_t* subcommand = useShortForm ? L"mf" : L"move-focus";
+
+        {
+            AppCommandlineArgs appArgs{};
+            std::vector<const wchar_t*> rawCommands{ L"wt.exe", subcommand };
+            Log::Comment(NoThrowString().Format(
+                L"Just the subcommand, without a direction, should fail."));
+
+            _buildCommandlinesExpectFailureHelper(appArgs, 1u, rawCommands);
+        }
+        {
+            AppCommandlineArgs appArgs{};
+            std::vector<const wchar_t*> rawCommands{ L"wt.exe", subcommand, L"left" };
+            _buildCommandlinesHelper(appArgs, 1u, rawCommands);
+
+            VERIFY_ARE_EQUAL(2u, appArgs._startupActions.size());
+
+            // The first action is going to always be a new-tab action
+            VERIFY_ARE_EQUAL(ShortcutAction::NewTab, appArgs._startupActions.at(0).Action());
+
+            auto actionAndArgs = appArgs._startupActions.at(1);
+            VERIFY_ARE_EQUAL(ShortcutAction::MoveFocus, actionAndArgs.Action());
+            VERIFY_IS_NOT_NULL(actionAndArgs.Args());
+            auto myArgs = actionAndArgs.Args().try_as<MoveFocusArgs>();
+            VERIFY_IS_NOT_NULL(myArgs);
+            VERIFY_ARE_EQUAL(FocusDirection::Left, myArgs.FocusDirection());
+        }
+        {
+            AppCommandlineArgs appArgs{};
+            std::vector<const wchar_t*> rawCommands{ L"wt.exe", subcommand, L"right" };
+            _buildCommandlinesHelper(appArgs, 1u, rawCommands);
+
+            VERIFY_ARE_EQUAL(2u, appArgs._startupActions.size());
+
+            // The first action is going to always be a new-tab action
+            VERIFY_ARE_EQUAL(ShortcutAction::NewTab, appArgs._startupActions.at(0).Action());
+
+            auto actionAndArgs = appArgs._startupActions.at(1);
+            VERIFY_ARE_EQUAL(ShortcutAction::MoveFocus, actionAndArgs.Action());
+            VERIFY_IS_NOT_NULL(actionAndArgs.Args());
+            auto myArgs = actionAndArgs.Args().try_as<MoveFocusArgs>();
+            VERIFY_IS_NOT_NULL(myArgs);
+            VERIFY_ARE_EQUAL(FocusDirection::Right, myArgs.FocusDirection());
+        }
+        {
+            AppCommandlineArgs appArgs{};
+            std::vector<const wchar_t*> rawCommands{ L"wt.exe", subcommand, L"up" };
+            _buildCommandlinesHelper(appArgs, 1u, rawCommands);
+
+            VERIFY_ARE_EQUAL(2u, appArgs._startupActions.size());
+
+            // The first action is going to always be a new-tab action
+            VERIFY_ARE_EQUAL(ShortcutAction::NewTab, appArgs._startupActions.at(0).Action());
+
+            auto actionAndArgs = appArgs._startupActions.at(1);
+            VERIFY_ARE_EQUAL(ShortcutAction::MoveFocus, actionAndArgs.Action());
+            VERIFY_IS_NOT_NULL(actionAndArgs.Args());
+            auto myArgs = actionAndArgs.Args().try_as<MoveFocusArgs>();
+            VERIFY_IS_NOT_NULL(myArgs);
+            VERIFY_ARE_EQUAL(FocusDirection::Up, myArgs.FocusDirection());
+        }
+        {
+            AppCommandlineArgs appArgs{};
+            std::vector<const wchar_t*> rawCommands{ L"wt.exe", subcommand, L"down" };
+            _buildCommandlinesHelper(appArgs, 1u, rawCommands);
+
+            VERIFY_ARE_EQUAL(2u, appArgs._startupActions.size());
+
+            // The first action is going to always be a new-tab action
+            VERIFY_ARE_EQUAL(ShortcutAction::NewTab, appArgs._startupActions.at(0).Action());
+
+            auto actionAndArgs = appArgs._startupActions.at(1);
+            VERIFY_ARE_EQUAL(ShortcutAction::MoveFocus, actionAndArgs.Action());
+            VERIFY_IS_NOT_NULL(actionAndArgs.Args());
+            auto myArgs = actionAndArgs.Args().try_as<MoveFocusArgs>();
+            VERIFY_IS_NOT_NULL(myArgs);
+            VERIFY_ARE_EQUAL(FocusDirection::Down, myArgs.FocusDirection());
+        }
+        {
+            AppCommandlineArgs appArgs{};
+            std::vector<const wchar_t*> rawCommands{ L"wt.exe", subcommand, L"badDirection" };
+            Log::Comment(NoThrowString().Format(
+                L"move-focus with an invalid direction should fail."));
+            _buildCommandlinesExpectFailureHelper(appArgs, 1u, rawCommands);
+        }
+        {
+            AppCommandlineArgs appArgs{};
+            std::vector<const wchar_t*> rawCommands{ L"wt.exe", subcommand, L"left", L";", subcommand, L"right" };
+            _buildCommandlinesHelper(appArgs, 2u, rawCommands);
+
+            VERIFY_ARE_EQUAL(3u, appArgs._startupActions.size());
+
+            // The first action is going to always be a new-tab action
+            VERIFY_ARE_EQUAL(ShortcutAction::NewTab, appArgs._startupActions.at(0).Action());
+
+            auto actionAndArgs = appArgs._startupActions.at(1);
+            VERIFY_ARE_EQUAL(ShortcutAction::MoveFocus, actionAndArgs.Action());
+            VERIFY_IS_NOT_NULL(actionAndArgs.Args());
+            auto myArgs = actionAndArgs.Args().try_as<MoveFocusArgs>();
+            VERIFY_IS_NOT_NULL(myArgs);
+            VERIFY_ARE_EQUAL(FocusDirection::Left, myArgs.FocusDirection());
+
+            actionAndArgs = appArgs._startupActions.at(2);
+            VERIFY_ARE_EQUAL(ShortcutAction::MoveFocus, actionAndArgs.Action());
+            VERIFY_IS_NOT_NULL(actionAndArgs.Args());
+            myArgs = actionAndArgs.Args().try_as<MoveFocusArgs>();
+            VERIFY_IS_NOT_NULL(myArgs);
+            VERIFY_ARE_EQUAL(FocusDirection::Right, myArgs.FocusDirection());
+        }
+    }
+
     void CommandlineTest::ValidateFirstCommandIsNewTab()
     {
         AppCommandlineArgs appArgs{};

src/cascadia/TerminalApp/AppCommandlineArgs.cpp

@@ -189,6 +189,7 @@ void AppCommandlineArgs::_buildParser()
     _buildNewTabParser();
     _buildSplitPaneParser();
     _buildFocusTabParser();
+    _buildMoveFocusParser();
 }
 
 // Method Description:
@@ -341,6 +342,54 @@ void AppCommandlineArgs::_buildFocusTabParser()
     setupSubcommand(_focusTabShort);
 }
 
+// Method Description:
+// - Adds the `move-focus` subcommand and related options to the commandline parser.
+// - Additionally adds the `mf` subcommand, which is just a shortened version of `move-focus`
+// Arguments:
+// - <none>
+// Return Value:
+// - <none>
+void AppCommandlineArgs::_buildMoveFocusParser()
+{
+    _moveFocusCommand = _app.add_subcommand("move-focus", RS_A(L"CmdMoveFocusDesc"));
+    _moveFocusShort = _app.add_subcommand("mf", RS_A(L"CmdMFDesc"));
+
+    auto setupSubcommand = [this](auto* subcommand) {
+        std::map<std::string, FocusDirection> map = {
+            { "left", FocusDirection::Left },
+            { "right", FocusDirection::Right },
+            { "up", FocusDirection::Up },
+            { "down", FocusDirection::Down }
+        };
+
+        auto* directionOpt = subcommand->add_option("direction",
+                                                    _moveFocusDirection,
+                                                    RS_A(L"CmdMoveFocusDirectionArgDesc"));
+
+        directionOpt->transform(CLI::CheckedTransformer(map, CLI::ignore_case));
+        directionOpt->required();
+        // When ParseCommand is called, if this subcommand was provided, this
+        // callback function will be triggered on the same thread. We can be sure
+        // that `this` will still be safe - this function just lets us know this
+        // command was parsed.
+        subcommand->callback([&, this]() {
+            if (_moveFocusDirection != FocusDirection::None)
+            {
+                MoveFocusArgs args{ _moveFocusDirection };
+
+                ActionAndArgs actionAndArgs{};
+                actionAndArgs.Action(ShortcutAction::MoveFocus);
+                actionAndArgs.Args(args);
+
+                _startupActions.push_back(std::move(actionAndArgs));
+            }
+        });
+    };
+
+    setupSubcommand(_moveFocusCommand);
+    setupSubcommand(_moveFocusShort);
+}
+
 // Method Description:
 // - Add the `NewTerminalArgs` parameters to the given subcommand. This enables
 //   that subcommand to support all the properties in a NewTerminalArgs.
@@ -448,6 +497,8 @@ bool AppCommandlineArgs::_noCommandsProvided()
              *_newTabShort.subcommand ||
              *_focusTabCommand ||
              *_focusTabShort ||
+             *_moveFocusCommand ||
+             *_moveFocusShort ||
              *_newPaneShort.subcommand ||
              *_newPaneCommand.subcommand);
 }
@@ -475,6 +526,7 @@ void AppCommandlineArgs::_resetStateToDefault()
     _focusNextTab = false;
     _focusPrevTab = false;
 
+    _moveFocusDirection = FocusDirection::None;
     // DON'T clear _launchMode here! This will get called once for every
     // subcommand, so we don't want `wt -F new-tab ; split-pane` clearing out
     // the "global" fullscreen flag (-F).

src/cascadia/TerminalApp/AppCommandlineArgs.h

@@ -74,13 +74,18 @@ class TerminalApp::AppCommandlineArgs final
     NewPaneSubcommand _newPaneShort;
     CLI::App* _focusTabCommand;
     CLI::App* _focusTabShort;
+    CLI::App* _moveFocusCommand;
+    CLI::App* _moveFocusShort;
+
     // Are you adding a new sub-command? Make sure to update _noCommandsProvided!
 
     std::string _profileName;
     std::string _startingDirectory;
     std::string _startingTitle;
     std::string _startingTabColor;
 
+    winrt::Microsoft::Terminal::Settings::Model::FocusDirection _moveFocusDirection{ winrt::Microsoft::Terminal::Settings::Model::FocusDirection::None };
+
     // _commandline will contain the command line with which we'll be spawning a new terminal
     std::vector<std::string> _commandline;
 
@@ -106,6 +111,7 @@ class TerminalApp::AppCommandlineArgs final
     void _buildNewTabParser();
     void _buildSplitPaneParser();
     void _buildFocusTabParser();
+    void _buildMoveFocusParser();
     bool _noCommandsProvided();
     void _resetStateToDefault();
     int _handleExit(const CLI::App& command, const CLI::Error& e);

src/cascadia/TerminalApp/Pane.cpp

@@ -583,6 +583,19 @@ void Pane::_FocusFirstChild()
 {
     if (_IsLeaf())
     {
+        if (_root.ActualWidth() == 0 && _root.ActualHeight() == 0)
+        {
+            // When these sizes are 0, then the pane might still be in startup,
+            // and doesn't yet have a real size. In that case, the control.Focus
+            // event won't be handled until _after_ the startup events are all
+            // processed. This will lead to the Tab not being notified that the
+            // focus moved to a different Pane.
+            //
+            // In that scenario, trigger the event manually here, to correctly
+            // inform the Tab that we're now focused.
+            _GotFocusHandlers(shared_from_this());
+        }
+
         _control.Focus(FocusState::Programmatic);
     }
     else

src/cascadia/TerminalApp/Resources/en-US/Resources.resw

@@ -318,6 +318,16 @@
   <data name="CmdFullscreenDesc" xml:space="preserve">
     <value>Launch the window in fullscreen mode</value>
   </data>
+  <data name="CmdMoveFocusDesc" xml:space="preserve">
+    <value>Move focus to the adjacent pane in the specified direction</value>
+  </data>
+  <data name="CmdMFDesc" xml:space="preserve">
+    <value>An alias for the "move-focus" subcommand.</value>
+    <comment>{Locked="\"move-focus\""}</comment>
+  </data>
+  <data name="CmdMoveFocusDirectionArgDesc" xml:space="preserve">
+    <value>The direction to move focus in</value>
+  </data>
   <data name="CmdFocusDesc" xml:space="preserve">
     <value>Launch the window in focus mode</value>
   </data>