Terminal: measure characters with Unicode 11 widths, so an emoji takes the two columns the remote counts

tests/DodoSSH.Client.Terminal.Tests/Renderer/renderer-harness.js

@@ -203,12 +203,22 @@ function FakeTerminal(options) {
   this.focuses = 0;
   this.disposed = false;
   this.pane = null;
+  this.addons = [];
+
+  // The proposed unicode API, at xterm's own default, so a test can see which table the page picked.
+  this.unicode = { activeVersion: '6' };
 
   terminals.push(this);
 }
 
-FakeTerminal.prototype.loadAddon = function () {};
-FakeTerminal.prototype.open = function (pane) { this.pane = pane; };
+FakeTerminal.prototype.loadAddon = function (addon) { this.addons.push(addon); };
+FakeTerminal.prototype.open = function (pane) {
+  this.pane = pane;
+
+  // Taken at open() because that is when the first frame is laid out: a table chosen afterwards would leave
+  // whatever was drawn first measured with the old one.
+  this.unicodeAtOpen = this.unicode.activeVersion;
+};
 FakeTerminal.prototype.attachCustomKeyEventHandler = function (handler) { this.keys = handler; };
 FakeTerminal.prototype.onData = function (handler) { this.data = handler; };
 FakeTerminal.prototype.onResize = function (handler) { this.resized = handler; };
@@ -242,6 +252,12 @@ var FitAddon = {
   },
 };
 
+var Unicode11Addon = {
+  Unicode11Addon: function () {
+    this.kind = 'unicode11';
+  },
+};
+
 var WebglAddon = {
   WebglAddon: function () {
     this.onContextLoss = function () {};
@@ -489,6 +505,16 @@ function typed(sessionId) {
   return terminalFor(sessionId).inputs.join('|');
 }
 
+/** Which character-width table the pane was opened with. */
+function unicodeAtOpen(sessionId) {
+  return terminalFor(sessionId).unicodeAtOpen;
+}
+
+/** Whether that pane loaded the Unicode 11 addon. */
+function hasUnicode11(sessionId) {
+  return terminalFor(sessionId).addons.some(function (addon) { return addon.kind === 'unicode11'; });
+}
+
 /** How many times that pane has been asked for the caret. */
 function focuses(sessionId) {
   return terminalFor(sessionId).focuses;

tests/DodoSSH.Client.Terminal.Tests/RendererPage.cs

@@ -94,6 +94,14 @@ internal sealed class RendererPage
     public string Typed(uint sessionId) =>
         engine.Evaluate(string.Create(CultureInfo.InvariantCulture, $"typed({sessionId})")).AsString();
 
+    /// <summary>Which character-width table that pane was opened with.</summary>
+    public string UnicodeAtOpen(uint sessionId) =>
+        engine.Evaluate(string.Create(CultureInfo.InvariantCulture, $"unicodeAtOpen({sessionId})")).AsString();
+
+    /// <summary>Whether that pane loaded the Unicode 11 addon.</summary>
+    public bool HasUnicode11(uint sessionId) =>
+        engine.Evaluate(string.Create(CultureInfo.InvariantCulture, $"hasUnicode11({sessionId})")).AsBoolean();
+
     /// <summary>How many times that session's pane has been asked for the caret.</summary>
     public int Focuses(uint sessionId) =>
         (int)engine.Evaluate(string.Create(CultureInfo.InvariantCulture, $"focuses({sessionId})")).AsNumber();

tests/DodoSSH.Client.Terminal.Tests/RendererUnicodeTests.cs

@@ -0,0 +1,43 @@
+namespace DodoSSH.Client.Terminal.Tests;
+
+/// <summary>
+/// The renderer page measures characters with Unicode 11's widths, so an emoji takes the two columns the
+/// remote counts for it.
+/// </summary>
+/// <remarks>
+/// What is asserted is that the page asks for the table, and asks before the first frame. Whether xterm then
+/// really draws 😀 across two cells is xterm's business, and the fake terminal in the harness is a stub with
+/// a memory, not an emulator; <c>docs/manual-checks.md</c> 1.13 is where a person looks at the real one.
+/// </remarks>
+public sealed class RendererUnicodeTests
+{
+    [Fact]
+    public void APane_LoadsTheUnicode11Addon()
+    {
+        var page = Opened();
+
+        page.HasUnicode11(7).ShouldBeTrue();
+    }
+
+    /// <remarks>
+    /// Before open() and not after it: a table chosen once the pane is open leaves whatever it drew first
+    /// measured with Unicode 6, which is the drift this exists to stop.
+    /// </remarks>
+    [Fact]
+    public void APane_IsOpenedWithUnicode11WidthsAlreadyActive()
+    {
+        var page = Opened();
+
+        page.UnicodeAtOpen(7).ShouldBe("11");
+    }
+
+    private static RendererPage Opened()
+    {
+        var page = RendererPage.Load();
+
+        page.Do("accept(0)");
+        page.Do("openSession(7)");
+
+        return page;
+    }
+}