From 22edbc1b373860be2230b88b2a5ec707b3ec0d4b Mon Sep 17 00:00:00 2001
From: Leonard Hecker <lhecker@microsoft.com>
Date: Thu, 11 Aug 2022 23:22:23 +0200
Subject: [PATCH] Fix issues with Japanese & Vietnamese IME (#13678)
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This commit builds directly on the changes made in #13677 and fixes:
* TSF resetting to AlphaNumeric ("ASCII") input mode when pressing enter
* Vietnamese IME not composing a new word after pressing whitespace, etc.

Closes #11479
Closes #13398

## Validation Steps Performed
* Japanese IME (Full-Width Katakana)
  Typing "saitama" produces "サイタマ" ✅
* Korean IME
  Typing "gksrmf" produces "한글" ✅
* Vietnamese IME
  Typing "xin chaof" produces "xin chào" ✅
* Emoji Picker (Win+.)
  ✅

(cherry picked from commit ed800dc72de9e51201becf1f752093f4c1b4e155)
Service-Card-Id: 84832470
Service-Version: 1.15
---
 .github/actions/spelling/expect/expect.txt    |  4 ++++
 .../TerminalControl/TSFInputControl.cpp       |  4 +---
 src/cascadia/TerminalControl/TermControl.cpp  | 19 +++++++++++++------
 3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/.github/actions/spelling/expect/expect.txt b/.github/actions/spelling/expect/expect.txt
index c1a1a3015f0..3b918c6ac4b 100644
--- a/.github/actions/spelling/expect/expect.txt
+++ b/.github/actions/spelling/expect/expect.txt
@@ -233,6 +233,7 @@ CFuzz
 cgscrn
 chafa
 changelist
+chaof
 charinfo
 charlespetzold
 charset
@@ -2892,6 +2893,9 @@ xff
 xfg
 XFile
 XFORM
+xin
+xinchaof
+xinxinchaof
 XManifest
 XMath
 XMFLOAT
diff --git a/src/cascadia/TerminalControl/TSFInputControl.cpp b/src/cascadia/TerminalControl/TSFInputControl.cpp
index 8cee7ffe154..7e9de19e99a 100644
--- a/src/cascadia/TerminalControl/TSFInputControl.cpp
+++ b/src/cascadia/TerminalControl/TSFInputControl.cpp
@@ -102,9 +102,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
             _inputBuffer.clear();
             _selection = {};
             _activeTextStart = 0;
-            _editContext.NotifyFocusLeave();
             _editContext.NotifyTextChanged({ 0, INT32_MAX }, 0, _selection);
-            _editContext.NotifyFocusEnter();
             TextBlock().Text({});
         }
     }
@@ -375,7 +373,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
                 incomingText);
             _selection = args.NewSelection();
             // GH#5054: Pressing backspace might move the caret before the _activeTextStart.
-            _activeTextStart = ::base::ClampMin(_activeTextStart, ::base::ClampedNumeric<size_t>(range.StartCaretPosition));
+            _activeTextStart = std::min(_activeTextStart, _inputBuffer.size());
 
             // Emojis/Kaomojis/Symbols chosen through the IME without starting composition
             // will be sent straight through to the terminal.
diff --git a/src/cascadia/TerminalControl/TermControl.cpp b/src/cascadia/TerminalControl/TermControl.cpp
index 91bcdac62f0..4896fa1aa37 100644
--- a/src/cascadia/TerminalControl/TermControl.cpp
+++ b/src/cascadia/TerminalControl/TermControl.cpp
@@ -904,6 +904,19 @@ namespace winrt::Microsoft::Terminal::Control::implementation
             return;
         }
 
+        // GH#11479: TSF wants to be notified of any character input via ICoreTextEditContext::NotifyTextChanged().
+        // TSF is built and tested around the idea that you inform it of any text changes that happen
+        // when it doesn't currently compose characters. For instance writing "xin chaof" with the
+        // Vietnamese IME should produce "xin chào". After writing "xin" it'll emit a composition
+        // completion event and we'll write "xin" to the shell. It now has no input focus and won't know
+        // about the whitespace. If you then write "chaof", it'll emit another composition completion
+        // event for "xinchaof" and the resulting output in the shell will finally read "xinxinchaof".
+        // A composition completion event technically doesn't mean that the completed text is now
+        // immutable after all. We could (and probably should) inform TSF of any input changes,
+        // but we technically aren't a text input field. The immediate solution was
+        // to simply force TSF to clear its text whenever we have input focus.
+        TSFInputControl().ClearBuffer();
+
         _HidePointerCursorHandlers(*this, nullptr);
 
         const auto ch = e.Character();
@@ -1165,12 +1178,6 @@ namespace winrt::Microsoft::Terminal::Control::implementation
     {
         const auto window = CoreWindow::GetForCurrentThread();
 
-        if (vkey == VK_ESCAPE ||
-            vkey == VK_RETURN)
-        {
-            TSFInputControl().ClearBuffer();
-        }
-
         // If the terminal translated the key, mark the event as handled.
         // This will prevent the system from trying to get the character out
         // of it and sending us a CharacterReceived event.