Improve handling of ambiguous diffs in contenteditable input mode

Author: marijnh

src/input/ContentEditableInput.js

@@ -279,6 +279,14 @@ export default class ContentEditableInput {
     while (cutEnd < maxCutEnd &&
            newBot.charCodeAt(newBot.length - cutEnd - 1) == oldBot.charCodeAt(oldBot.length - cutEnd - 1))
       ++cutEnd
+    // Try to move start of change to start of selection if ambiguous
+    if (newText.length == 1 && oldText.length == 1 && fromLine == from.line) {
+      while (cutFront && cutFront > from.ch &&
+             newBot.charCodeAt(newBot.length - cutEnd - 1) == oldBot.charCodeAt(oldBot.length - cutEnd - 1)) {
+        cutFront--
+        cutEnd++
+      }
+    }
 
     newText[newText.length - 1] = newBot.slice(0, newBot.length - cutEnd).replace(/^\u200b+/, "")
     newText[0] = newText[0].slice(cutFront).replace(/\u200b+$/, "")

test/contenteditable_test.js

@@ -60,6 +60,27 @@
     eq(cm.getValue(), "one\ntwothree\nfour\n")
   }, {inputStyle: "contenteditable", value: "one\ntwo\nfoo\nbar\nthree\nfour\n"})
 
+  testCM("ambiguous_diff_middle", function(cm) {
+    cm.setSelection(Pos(0, 2))
+    findTextNode(cm, "baah").nodeValue = "baaah"
+    cm.display.input.updateFromDOM()
+    eqCharPos(cm.getCursor(), Pos(0, 3))
+  }, {inputStyle: "contenteditable", value: "baah"})
+
+  testCM("ambiguous_diff_start", function(cm) {
+    cm.setSelection(Pos(0, 1))
+    findTextNode(cm, "baah").nodeValue = "baaah"
+    cm.display.input.updateFromDOM()
+    eqCharPos(cm.getCursor(), Pos(0, 2))
+  }, {inputStyle: "contenteditable", value: "baah"})
+
+  testCM("ambiguous_diff_end", function(cm) {
+    cm.setSelection(Pos(0, 3))
+    findTextNode(cm, "baah").nodeValue = "baaah"
+    cm.display.input.updateFromDOM()
+    eqCharPos(cm.getCursor(), Pos(0, 4))
+  }, {inputStyle: "contenteditable", value: "baah"})
+
   testCM("force_redraw", function(cm) {
     findTextNode(cm, "foo").parentNode.appendChild(document.createElement("hr")).className = "inserted"
     cm.display.input.updateFromDOM()