Add an experimental setting for moving the cursor with the mouse (#15758

)

## Summary of the Pull Request

This adds a new experimental per-setting to the terminal. 

```ts
"experimental.repositionCursorWithMouse": bool
```

When:
* the setting is on 
* AND you turn on shell integration (at least `133;B`)
* AND you click is somewhere _after_ the "active command" mark

we'll send a number of simulated keystrokes to the terminal based off
the number of cells between the place clicked and where the current
mouse cursor is.


## PR Checklist
- [ ] Related to #8573. I'm not marking as _closed_, because we should
probably polish this before we close that out. This is more a place to
start.

## Detailed Description of the Pull Request / Additional comments

There was a LOT of discussion in #8573. This is kinda a best effort
feature - it won't always work, but it should improve the experience
_most of the time_. We all kinda agreed that as much as the shell
probably should be responsible for doing this, there's myriad reasons
that won't work in practicality:
* That would also disable selection made by the terminal. That's a hard
sell.
* We'd need to invent some new mouse mode to support
click-to-reposition-but-drags-to-select-I-don't-want
* We'd then need shells to adopt that functionality.

And eventually settled that this was the least horrifying comprimise.

This has _e d g e  c a s e s_: 
* Does it work for wrapped lines? Well, kinda okay actually.
* Does it work for `vim`/`emacs`? Nope. 
* Does it work for emoji/wide glyphs? I wouldn't expect it to! I mean,
emoji input is messed up anyways, right?
* Other characters like `ESC` (which are rendered by the shell as two
cells "^[")? Nope.
* Does it do selections? Nope.
* Clicking across lines with continuation prompts? Nope.
* Tabs? Nope.
* Wraps within tmux/screen? Nope.


https://github.com/xtermjs/xterm.js/blob/master/src/browser/input/MoveToCell.ts
has probably a more complete implementation of how we'd want to generate
the keypresses and such.

src/buffer/out/textBuffer.cpp

@@ -246,6 +246,27 @@ til::CoordType TextBuffer::TotalRowCount() const noexcept
     return _height;
 }
 
+// Method Description:
+// - Gets the number of glyphs in the buffer between two points.
+// - IMPORTANT: Make sure that start is before end, or this will never return!
+// Arguments:
+// - start - The starting point of the range to get the glyph count for.
+// - end - The ending point of the range to get the glyph count for.
+// Return Value:
+// - The number of glyphs in the buffer between the two points.
+size_t TextBuffer::GetCellDistance(const til::point from, const til::point to) const
+{
+    auto startCell = GetCellDataAt(from);
+    const auto endCell = GetCellDataAt(to);
+    auto delta = 0;
+    while (startCell != endCell)
+    {
+        ++startCell;
+        ++delta;
+    }
+    return delta;
+}
+
 // Routine Description:
 // - Retrieves read-only text iterator at the given buffer location
 // Arguments:

src/buffer/out/textBuffer.hpp

@@ -131,6 +131,8 @@ class TextBuffer final
     TextBufferTextIterator GetTextLineDataAt(const til::point at) const;
     TextBufferTextIterator GetTextDataAt(const til::point at, const Microsoft::Console::Types::Viewport limit) const;
 
+    size_t GetCellDistance(const til::point from, const til::point to) const;
+
     static size_t GraphemeNext(const std::wstring_view& chars, size_t position) noexcept;
     static size_t GraphemePrev(const std::wstring_view& chars, size_t position) noexcept;
 

src/cascadia/TerminalControl/ControlCore.cpp

@@ -1754,6 +1754,73 @@ namespace winrt::Microsoft::Terminal::Control::implementation
             _terminal->MultiClickSelection(terminalPosition, mode);
             selectionNeedsToBeCopied = true;
         }
+        else if (_settings->RepositionCursorWithMouse()) // This is also mode==Char && !shiftEnabled
+        {
+            // If we're handling a single left click, without shift pressed, and
+            // outside mouse mode, AND the user has RepositionCursorWithMouse turned
+            // on, let's try to move the cursor.
+            //
+            // We'll only move the cursor if the user has clicked after the last
+            // mark, if there is one. That means the user also needs to set up
+            // shell integration to enable this feature.
+            //
+            // As noted in GH #8573, there's plenty of edge cases with this
+            // approach, but it's good enough to bring value to 90% of use cases.
+            const auto cursorPos{ _terminal->GetCursorPosition() };
+
+            // Does the current buffer line have a mark on it?
+            const auto& marks{ _terminal->GetScrollMarks() };
+            if (!marks.empty())
+            {
+                const auto& last{ marks.back() };
+                const auto [start, end] = last.GetExtent();
+                const auto lastNonSpace = _terminal->GetTextBuffer().GetLastNonSpaceCharacter();
+
+                // If the user clicked off to the right side of the prompt, we
+                // want to send keystrokes to the last character in the prompt +1.
+                //
+                // We don't want to send too many here. In CMD, if the user's
+                // last command is longer than what they've currently typed, and
+                // they press right arrow at the end of the prompt, COOKED_READ
+                // will fill in characters from the previous command.
+                //
+                // By only sending keypresses to the end of the command + 1, we
+                // should leave the cursor at the very end of the prompt,
+                // without adding any characters from a previous command.
+                auto clampedClick = terminalPosition;
+                if (terminalPosition > lastNonSpace)
+                {
+                    clampedClick = lastNonSpace + til::point{ 1, 0 };
+                    _terminal->GetTextBuffer().GetSize().Clamp(clampedClick);
+                }
+
+                if (clampedClick >= end)
+                {
+                    // Get the distance between the cursor and the click, in cells.
+                    const auto bufferSize = _terminal->GetTextBuffer().GetSize();
+
+                    // First, make sure to iterate from the first point to the
+                    // second. The user may have clicked _earlier_ in the
+                    // buffer!
+                    auto goRight = clampedClick > cursorPos;
+                    const auto startPoint = goRight ? cursorPos : clampedClick;
+                    const auto endPoint = goRight ? clampedClick : cursorPos;
+
+                    const auto delta = _terminal->GetTextBuffer().GetCellDistance(startPoint, endPoint);
+
+                    const WORD key = goRight ? VK_RIGHT : VK_LEFT;
+                    // Send an up and a down once per cell. This won't
+                    // accurately handle wide characters, or continuation
+                    // prompts, or cases where a single escape character in the
+                    // command (e.g. ^[) takes up two cells.
+                    for (size_t i = 0u; i < delta; i++)
+                    {
+                        _terminal->SendKeyEvent(key, 0, {}, true);
+                        _terminal->SendKeyEvent(key, 0, {}, false);
+                    }
+                }
+            }
+        }
         _updateSelectionUI();
     }
 

src/cascadia/TerminalControl/IControlSettings.idl

@@ -61,5 +61,6 @@ namespace Microsoft.Terminal.Control
         Boolean ShowMarks { get; };
         Boolean UseBackgroundImageForWindow { get; };
         Boolean RightClickContextMenu { get; };
+        Boolean RepositionCursorWithMouse { get; };
     };
 }

src/cascadia/TerminalSettingsModel/MTSMSettings.h

@@ -69,6 +69,12 @@ Author(s):
     X(bool, IsolatedMode, "compatibility.isolatedMode", false)                                                                                                                                        \
     X(hstring, SearchWebDefaultQueryUrl, "searchWebDefaultQueryUrl", L"https://www.bing.com/search?q=%22%s%22")
 
+// Also add these settings to:
+// * Profile.idl
+// * TerminalSettings.h
+// * TerminalSettings.cpp: TerminalSettings::_ApplyProfileSettings
+// * IControlSettings.idl or ICoreSettings.idl
+// * ControlProperties.h
 #define MTSM_PROFILE_SETTINGS(X)                                                                                                                               \
     X(int32_t, HistorySize, "historySize", DEFAULT_HISTORY_SIZE)                                                                                               \
     X(bool, SnapOnInput, "snapOnInput", true)                                                                                                                  \
@@ -91,7 +97,8 @@ Author(s):
     X(bool, Elevate, "elevate", false)                                                                                                                         \
     X(bool, VtPassthrough, "experimental.connection.passthroughMode", false)                                                                                   \
     X(bool, AutoMarkPrompts, "experimental.autoMarkPrompts", false)                                                                                            \
-    X(bool, ShowMarks, "experimental.showMarksOnScrollbar", false)
+    X(bool, ShowMarks, "experimental.showMarksOnScrollbar", false)                                                                                             \
+    X(bool, RepositionCursorWithMouse, "experimental.repositionCursorWithMouse", false)
 
 // Intentionally omitted Profile settings:
 // * Name

src/cascadia/TerminalSettingsModel/Profile.idl

@@ -94,5 +94,6 @@ namespace Microsoft.Terminal.Settings.Model
         INHERITABLE_PROFILE_SETTING(Boolean, ShowMarks);
 
         INHERITABLE_PROFILE_SETTING(Boolean, RightClickContextMenu);
+        INHERITABLE_PROFILE_SETTING(Boolean, RepositionCursorWithMouse);
     }
 }

src/cascadia/TerminalSettingsModel/TerminalSettings.cpp

@@ -325,6 +325,8 @@ namespace winrt::Microsoft::Terminal::Settings::Model::implementation
         _ShowMarks = Feature_ScrollbarMarks::IsEnabled() && profile.ShowMarks();
 
         _RightClickContextMenu = profile.RightClickContextMenu();
+
+        _RepositionCursorWithMouse = profile.RepositionCursorWithMouse();
     }
 
     // Method Description:

src/cascadia/TerminalSettingsModel/TerminalSettings.h

@@ -164,6 +164,7 @@ namespace winrt::Microsoft::Terminal::Settings::Model::implementation
         INHERITABLE_SETTING(Model::TerminalSettings, bool, AutoMarkPrompts, false);
         INHERITABLE_SETTING(Model::TerminalSettings, bool, ShowMarks, false);
         INHERITABLE_SETTING(Model::TerminalSettings, bool, RightClickContextMenu, false);
+        INHERITABLE_SETTING(Model::TerminalSettings, bool, RepositionCursorWithMouse, false);
 
     private:
         std::optional<std::array<Microsoft::Terminal::Core::Color, COLOR_TABLE_SIZE>> _ColorTable;

src/cascadia/UnitTests_Control/ControlCoreTests.cpp

@@ -41,6 +41,8 @@ namespace ControlUnitTests
         TEST_METHOD(TestSelectCommandSimple);
         TEST_METHOD(TestSelectOutputSimple);
 
+        TEST_METHOD(TestSimpleClickSelection);
+
         TEST_CLASS_SETUP(ModuleSetup)
         {
             winrt::init_apartment(winrt::apartment_type::single_threaded);
@@ -499,4 +501,68 @@ namespace ControlUnitTests
             VERIFY_ARE_EQUAL(expectedEnd, end);
         }
     }
+
+    void ControlCoreTests::TestSimpleClickSelection()
+    {
+        // Create a simple selection with the mouse, then click somewhere else,
+        // and confirm the selection got updated.
+
+        auto [settings, conn] = _createSettingsAndConnection();
+        Log::Comment(L"Create ControlCore object");
+        auto core = createCore(*settings, *conn);
+        VERIFY_IS_NOT_NULL(core);
+        _standardInit(core);
+
+        // Here, we're using the UpdateSelectionMarkers as a stand-in to check
+        // if the selection got updated with the renderer. Standing up a whole
+        // dummy renderer for this test would be not very ergonomic. Instead, we
+        // are relying on ControlCore::_updateSelectionUI both
+        // TriggerSelection()'ing and also rasing this event
+        bool expectedSelectionUpdate = false;
+        bool gotSelectionUpdate = false;
+        core->UpdateSelectionMarkers([&](auto&& /*sender*/, auto&& /*args*/) {
+            VERIFY_IS_TRUE(expectedSelectionUpdate);
+            expectedSelectionUpdate = false;
+            gotSelectionUpdate = true;
+        });
+
+        auto needToCopy = false;
+        expectedSelectionUpdate = true;
+        core->LeftClickOnTerminal(til::point{ 1, 1 },
+                                  1,
+                                  false,
+                                  true,
+                                  false,
+                                  needToCopy);
+
+        VERIFY_IS_TRUE(core->HasSelection());
+        {
+            const auto& start = core->_terminal->GetSelectionAnchor();
+            const auto& end = core->_terminal->GetSelectionEnd();
+            const til::point expectedStart{ 1, 1 };
+            const til::point expectedEnd{ 1, 1 };
+            VERIFY_ARE_EQUAL(expectedStart, start);
+            VERIFY_ARE_EQUAL(expectedEnd, end);
+        }
+        VERIFY_IS_TRUE(gotSelectionUpdate);
+
+        expectedSelectionUpdate = true;
+        core->LeftClickOnTerminal(til::point{ 1, 2 },
+                                  1,
+                                  false,
+                                  true,
+                                  false,
+                                  needToCopy);
+
+        VERIFY_IS_TRUE(core->HasSelection());
+        {
+            const auto& start = core->_terminal->GetSelectionAnchor();
+            const auto& end = core->_terminal->GetSelectionEnd();
+            const til::point expectedStart{ 1, 1 };
+            const til::point expectedEnd{ 1, 2 };
+            VERIFY_ARE_EQUAL(expectedStart, start);
+            VERIFY_ARE_EQUAL(expectedEnd, end);
+        }
+        VERIFY_IS_TRUE(gotSelectionUpdate);
+    }
 }

src/cascadia/inc/ControlProperties.h

@@ -47,7 +47,8 @@
     X(winrt::hstring, StartingTitle)                                                                              \
     X(bool, DetectURLs, true)                                                                                     \
     X(bool, VtPassthrough, false)                                                                                 \
-    X(bool, AutoMarkPrompts)
+    X(bool, AutoMarkPrompts)                                                                                      \
+    X(bool, RepositionCursorWithMouse, false)
 
 // --------------------------- Control Settings ---------------------------
 //  All of these settings are defined in IControlSettings.