Refactor the SettingsTab to be a pane (#16172)

... technically. We still won't let it actually _be_ a pane, but now it
acts like one. It's hosted in a `SettingsPaneContent`. There's no more
`SettingsTab`. It totally _can_ be in a pane (but don't?)

## Validation Steps Performed

* Still opens the settings
* Only opens a single settings tab, or re-activates the existing one
* Session restores!
* Updates the title of the tab appropriately
* I previously _did_ use the scratchpad action to open the settings in a
pane, and that worked.

## Related PRs
* #16170
  * #16171 
    * #16172 <-- you are here 
      * #16895

Refs #997
Closes #8452

src/cascadia/TerminalApp/AppActionHandlers.cpp

@@ -1418,7 +1418,7 @@ namespace winrt::TerminalApp::implementation
         args.Handled(true);
     }
 
-    void TerminalPage::_HandleOpenScratchpad(const IInspectable& /*sender*/,
+    void TerminalPage::_HandleOpenScratchpad(const IInspectable& sender,
                                              const ActionEventArgs& args)
     {
         if (Feature_ScratchpadPane::IsEnabled())
@@ -1431,7 +1431,7 @@ namespace winrt::TerminalApp::implementation
             scratchPane->GetRoot().KeyDown({ this, &TerminalPage::_KeyDownHandler });
 
             const auto resultPane = std::make_shared<Pane>(*scratchPane);
-            _SplitPane(_GetFocusedTabImpl(), SplitDirection::Automatic, 0.5f, resultPane);
+            _SplitPane(_senderOrFocusedTab(sender), SplitDirection::Automatic, 0.5f, resultPane);
             args.Handled(true);
         }
     }

src/cascadia/TerminalApp/IPaneContent.idl

@@ -19,13 +19,17 @@ namespace TerminalApp
     interface IPaneContent
     {
         Windows.UI.Xaml.FrameworkElement GetRoot();
+        void UpdateSettings(Microsoft.Terminal.Settings.Model.CascadiaSettings settings);
 
         Windows.Foundation.Size MinimumSize { get; };
 
         String Title { get; };
         UInt64 TaskbarState { get; };
         UInt64 TaskbarProgress { get; };
         Boolean ReadOnly { get; };
+        String Icon { get; };
+        Windows.Foundation.IReference<Windows.UI.Color> TabColor { get; };
+        Windows.UI.Xaml.Media.Brush BackgroundBrush { get; };
 
         Microsoft.Terminal.Settings.Model.NewTerminalArgs GetNewTerminalArgs(BuildStartupKind kind);
 

src/cascadia/TerminalApp/Pane.cpp

@@ -1075,6 +1075,29 @@ TermControl Pane::GetLastFocusedTerminalControl()
     return GetTerminalControl();
 }
 
+IPaneContent Pane::GetLastFocusedContent()
+{
+    if (!_IsLeaf())
+    {
+        if (_lastActive)
+        {
+            auto pane = shared_from_this();
+            while (const auto p = pane->_parentChildPath.lock())
+            {
+                if (p->_IsLeaf())
+                {
+                    return p->_content;
+                }
+                pane = p;
+            }
+            // We didn't find our child somehow, they might have closed under us.
+        }
+        return _firstChild->GetLastFocusedContent();
+    }
+
+    return _content;
+}
+
 // Method Description:
 // - Gets the TermControl of this pane. If this Pane is not a leaf this will
 //   return the nullptr;
@@ -1215,7 +1238,10 @@ void Pane::UpdateVisuals()
 void Pane::_Focus()
 {
     GotFocus.raise(shared_from_this(), FocusState::Programmatic);
-    _content.Focus(FocusState::Programmatic);
+    if (const auto& lastContent{ GetLastFocusedContent() })
+    {
+        lastContent.Focus(FocusState::Programmatic);
+    }
 }
 
 // Method Description:
@@ -1254,20 +1280,21 @@ void Pane::_FocusFirstChild()
     }
 }
 
-// Method Description:
-// - Updates the settings of this pane, presuming that it is a leaf.
-// Arguments:
-// - settings: The new TerminalSettings to apply to any matching controls
-// - profile: The profile from which these settings originated.
-// Return Value:
-// - <none>
-void Pane::UpdateSettings(const TerminalSettingsCreateResult& settings, const Profile& profile)
+void Pane::UpdateSettings(const CascadiaSettings& settings, const winrt::TerminalApp::TerminalSettingsCache& cache)
 {
-    assert(_IsLeaf());
-
-    if (const auto& terminalPane{ _getTerminalContent() })
+    if (_content)
     {
-        return terminalPane.UpdateSettings(settings, profile);
+        // We need to do a bit more work here for terminal
+        // panes. They need to know about the profile that was used for
+        // them, and about the focused/unfocused settings.
+        if (const auto& terminalPaneContent{ _content.try_as<TerminalPaneContent>() })
+        {
+            terminalPaneContent.UpdateTerminalSettings(cache);
+        }
+        else
+        {
+            _content.UpdateSettings(settings);
+        }
     }
 }
 
@@ -1893,7 +1920,7 @@ void Pane::_SetupEntranceAnimation()
         auto child = isFirstChild ? _firstChild : _secondChild;
         auto childGrid = child->_root;
         // If we are splitting a parent pane this may be null
-        auto control = child->_content.GetRoot();
+        auto control = child->_content ? child->_content.GetRoot() : nullptr;
         // Build up our animation:
         // * it'll take as long as our duration (200ms)
         // * it'll change the value of our property from 0 to secondSize

src/cascadia/TerminalApp/Pane.h

@@ -73,6 +73,7 @@ class Pane : public std::enable_shared_from_this<Pane>
 
     std::shared_ptr<Pane> GetActivePane();
     winrt::Microsoft::Terminal::Control::TermControl GetLastFocusedTerminalControl();
+    winrt::TerminalApp::IPaneContent GetLastFocusedContent();
     winrt::Microsoft::Terminal::Control::TermControl GetTerminalControl() const;
     winrt::Microsoft::Terminal::Settings::Model::Profile GetFocusedProfile();
     bool IsConnectionClosed() const;
@@ -107,8 +108,7 @@ class Pane : public std::enable_shared_from_this<Pane>
     BuildStartupState BuildStartupActions(uint32_t currentId, uint32_t nextId, winrt::TerminalApp::BuildStartupKind kind);
     winrt::Microsoft::Terminal::Settings::Model::NewTerminalArgs GetTerminalArgsForPane(winrt::TerminalApp::BuildStartupKind kind) const;
 
-    void UpdateSettings(const winrt::Microsoft::Terminal::Settings::Model::TerminalSettingsCreateResult& settings,
-                        const winrt::Microsoft::Terminal::Settings::Model::Profile& profile);
+    void UpdateSettings(const winrt::Microsoft::Terminal::Settings::Model::CascadiaSettings& settings, const winrt::TerminalApp::TerminalSettingsCache& cache);
     bool ResizePane(const winrt::Microsoft::Terminal::Settings::Model::ResizeDirection& direction);
     std::shared_ptr<Pane> NavigateDirection(const std::shared_ptr<Pane> sourcePane,
                                             const winrt::Microsoft::Terminal::Settings::Model::FocusDirection& direction,

src/cascadia/TerminalApp/ScratchpadContent.cpp

@@ -26,6 +26,11 @@ namespace winrt::TerminalApp::implementation
         _root.Children().Append(_box);
     }
 
+    void ScratchpadContent::UpdateSettings(const CascadiaSettings& /*settings*/)
+    {
+        // Nothing to do.
+    }
+
     winrt::Windows::UI::Xaml::FrameworkElement ScratchpadContent::GetRoot()
     {
         return _root;
@@ -47,4 +52,15 @@ namespace winrt::TerminalApp::implementation
     {
         return nullptr;
     }
+
+    winrt::hstring ScratchpadContent::Icon() const
+    {
+        static constexpr std::wstring_view glyph{ L"\xe70b" }; // QuickNote
+        return winrt::hstring{ glyph };
+    }
+
+    winrt::Windows::UI::Xaml::Media::Brush ScratchpadContent::BackgroundBrush()
+    {
+        return _root.Background();
+    }
 }

src/cascadia/TerminalApp/ScratchpadContent.h

@@ -13,6 +13,8 @@ namespace winrt::TerminalApp::implementation
 
         winrt::Windows::UI::Xaml::FrameworkElement GetRoot();
 
+        void UpdateSettings(const winrt::Microsoft::Terminal::Settings::Model::CascadiaSettings& settings);
+
         winrt::Windows::Foundation::Size MinimumSize();
 
         void Focus(winrt::Windows::UI::Xaml::FocusState reason = winrt::Windows::UI::Xaml::FocusState::Programmatic);
@@ -23,6 +25,9 @@ namespace winrt::TerminalApp::implementation
         uint64_t TaskbarState() { return 0; }
         uint64_t TaskbarProgress() { return 0; }
         bool ReadOnly() { return false; }
+        winrt::hstring Icon() const;
+        Windows::Foundation::IReference<winrt::Windows::UI::Color> TabColor() const noexcept { return nullptr; }
+        winrt::Windows::UI::Xaml::Media::Brush BackgroundBrush();
 
         til::typed_event<> ConnectionStateChanged;
         til::typed_event<IPaneContent> CloseRequested;

src/cascadia/TerminalApp/SettingsPaneContent.cpp

@@ -0,0 +1,84 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+#include "pch.h"
+#include "SettingsPaneContent.h"
+#include "Utils.h"
+
+using namespace winrt::Windows::Foundation;
+using namespace winrt::Windows::UI::Xaml;
+using namespace winrt::Microsoft::Terminal::Settings::Model;
+
+#define ASSERT_UI_THREAD() assert(_sui.Dispatcher().HasThreadAccess())
+
+namespace winrt::TerminalApp::implementation
+{
+    SettingsPaneContent::SettingsPaneContent(CascadiaSettings settings)
+    {
+        _sui = winrt::Microsoft::Terminal::Settings::Editor::MainPage{ settings };
+
+        // Stash away the current requested theme of the app. We'll need that in
+        // _BackgroundBrush() to do a theme-aware resource lookup
+        _requestedTheme = settings.GlobalSettings().CurrentTheme().RequestedTheme();
+    }
+
+    void SettingsPaneContent::UpdateSettings(const CascadiaSettings& settings)
+    {
+        ASSERT_UI_THREAD();
+        _sui.UpdateSettings(settings);
+
+        _requestedTheme = settings.GlobalSettings().CurrentTheme().RequestedTheme();
+    }
+
+    winrt::Windows::UI::Xaml::FrameworkElement SettingsPaneContent::GetRoot()
+    {
+        return _sui;
+    }
+    winrt::Windows::Foundation::Size SettingsPaneContent::MinimumSize()
+    {
+        return { 1, 1 };
+    }
+    void SettingsPaneContent::Focus(winrt::Windows::UI::Xaml::FocusState reason)
+    {
+        if (reason != FocusState::Unfocused)
+        {
+            _sui.as<Controls::Page>().Focus(reason);
+        }
+    }
+    void SettingsPaneContent::Close()
+    {
+        CloseRequested.raise(*this, nullptr);
+    }
+
+    NewTerminalArgs SettingsPaneContent::GetNewTerminalArgs(const BuildStartupKind /*kind*/) const
+    {
+        // For now, we're doing a terrible thing in TerminalTab itself to
+        // generate an OpenSettings action manually, without asking for the pane
+        // structure.
+        return nullptr;
+    }
+
+    winrt::hstring SettingsPaneContent::Icon() const
+    {
+        // This is the Setting icon (looks like a gear)
+        static constexpr std::wstring_view glyph{ L"\xE713" };
+        return winrt::hstring{ glyph };
+    }
+
+    Windows::Foundation::IReference<winrt::Windows::UI::Color> SettingsPaneContent::TabColor() const noexcept
+    {
+        return nullptr;
+    }
+
+    winrt::Windows::UI::Xaml::Media::Brush SettingsPaneContent::BackgroundBrush()
+    {
+        // Look up the color we should use for the settings tab item from our
+        // resources. This should only be used for when "terminalBackground" is
+        // requested.
+        static const auto key = winrt::box_value(L"SettingsUiTabBrush");
+        // You can't just do a Application::Current().Resources().TryLookup
+        // lookup, cause the app theme never changes! Do the hacky version
+        // instead.
+        return ThemeLookup(Application::Current().Resources(), _requestedTheme, key).try_as<winrt::Windows::UI::Xaml::Media::Brush>();
+    }
+}

src/cascadia/TerminalApp/SettingsPaneContent.h

@@ -0,0 +1,46 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT license.
+
+#pragma once
+#include "winrt/TerminalApp.h"
+#include <LibraryResources.h>
+
+namespace winrt::TerminalApp::implementation
+{
+    class SettingsPaneContent : public winrt::implements<SettingsPaneContent, IPaneContent>
+    {
+    public:
+        SettingsPaneContent(winrt::Microsoft::Terminal::Settings::Model::CascadiaSettings settings);
+
+        void UpdateSettings(const winrt::Microsoft::Terminal::Settings::Model::CascadiaSettings& settings);
+
+        winrt::Windows::UI::Xaml::FrameworkElement GetRoot();
+        winrt::Microsoft::Terminal::Settings::Editor::MainPage SettingsUI() { return _sui; }
+
+        winrt::Windows::Foundation::Size MinimumSize();
+        void Focus(winrt::Windows::UI::Xaml::FocusState reason = winrt::Windows::UI::Xaml::FocusState::Programmatic);
+        void Close();
+        winrt::Microsoft::Terminal::Settings::Model::NewTerminalArgs GetNewTerminalArgs(const BuildStartupKind kind) const;
+
+        winrt::hstring Title() { return RS_(L"SettingsTab"); }
+        uint64_t TaskbarState() { return 0; }
+        uint64_t TaskbarProgress() { return 0; }
+        bool ReadOnly() { return false; }
+        winrt::hstring Icon() const;
+        Windows::Foundation::IReference<winrt::Windows::UI::Color> TabColor() const noexcept;
+        winrt::Windows::UI::Xaml::Media::Brush BackgroundBrush();
+
+        til::typed_event<> ConnectionStateChanged;
+        til::typed_event<IPaneContent> CloseRequested;
+        til::typed_event<IPaneContent, winrt::TerminalApp::BellEventArgs> BellRequested;
+        til::typed_event<IPaneContent> TitleChanged;
+        til::typed_event<IPaneContent> TabColorChanged;
+        til::typed_event<IPaneContent> TaskbarProgressChanged;
+        til::typed_event<IPaneContent> ReadOnlyChanged;
+        til::typed_event<IPaneContent> FocusRequested;
+
+    private:
+        winrt::Microsoft::Terminal::Settings::Editor::MainPage _sui{ nullptr };
+        winrt::Windows::UI::Xaml::ElementTheme _requestedTheme;
+    };
+}