Manual edit: Simplify add/remove of full lines

Always choose the simplest diff.

nbdime-web/src/common/mergeview.ts

@@ -50,7 +50,7 @@ import {
 } from './exceptions';
 
 import {
-  updateModel
+  updateModel, shiftAddRemoveLines
 } from '../merge/manualedit';
 
 
@@ -375,12 +375,13 @@ class DiffView {
       debounceChange = window.setTimeout(
         update.bind(self, mode), fast === true ? 20 : 250);
     }
-    function change(_cm: CodeMirror.Editor, change: CodeMirror.EditorChangeLinkedList) {
+    function change(_cm: CodeMirror.Editor, change: CodeMirror.EditorChange) {
       let userEdit = !valueIn(change.origin, ['setValue', 'syncModel']);
       if (userEdit) {
         // Edited by hand!
-        let baseLine = getMatchingBaseLine(change.from.line, self.lineChunks);
         let fullLines = splitLines(self.model.remote!);
+        shiftAddRemoveLines(fullLines, change);
+        let baseLine = getMatchingBaseLine(change.from.line, self.lineChunks);
         // Update lines with changes
         replaceCodeMirrorRange(fullLines, change.from, change.to, change.text);
         updateModel({

nbdime-web/src/merge/manualedit.ts

@@ -214,7 +214,7 @@ function getPartials(diff: AddRem[], options: IUpdateModelOptions, startOffset:
   let line = options.baseLine;
   let ch = options.editCh;
   let {oldval, newval} = options;
-  let lines: string[] | null = null;
+  let lines: string[] = options.fullLines;
   let key = line;
   let linediff = 0;
 
@@ -245,14 +245,12 @@ function getPartials(diff: AddRem[], options: IUpdateModelOptions, startOffset:
     } else if (partialStart) {
       // Addrange before current line (abutting)
       // and partial edit of current (unedited) line
-      lines = options.fullLines;
       before.push(lines[options.editLine].slice(0, ch));
       // Indicate that one unedited line should be removed
       linediff = 1;
     }
   } else if (partialStart) {
     // Replace previously unedited line:
-    lines = options.fullLines;
     before = [lines[options.editLine].slice(0, ch)];
     // Indicate that one unedited line should be removed
     linediff = 1;
@@ -279,9 +277,6 @@ function getPartials(diff: AddRem[], options: IUpdateModelOptions, startOffset:
   }
   if (!after && !fullDeleteEnd && !fullLineInsertions) {
     // Add remains of previously unedited line
-    if (lines === null) {
-      lines = options.fullLines;
-    }
     let fullLine = lines[options.editLine + newval.length - 1];
     let cut = lastAddedLine.length;
     if (newval.length === 1) {
@@ -773,6 +768,81 @@ function patchPatchedModel(options: IUpdateModelOptions, diffs: 'all' | 'custom'
   // Add new decisions for changes that do no overlap
 }
 
+
+/**
+ * Modify certain edits to use trailing newlines instead of leading
+ *
+ * Certain edits, e.g. adding a newline link this (bracketed part added):
+ *   line1[\n
+ *   line2]\n
+ * can better be treated as:
+ *   line1\n
+ *   [line2\n]
+ *
+ * Similarly (bracketed part deleted):
+ *   line1[\n
+ *   line2]\n
+ * can better be treated as:
+ *   line1\n
+ *   [line2\n]
+ *
+ * The end results are the same, but the diffs become simpler.
+ *
+ * Note that this needs to be called before base line is computed!
+ */
+export
+function shiftAddRemoveLines(base: string[], change: CodeMirror.EditorChange) {
+  if (change.from.ch === 0) {
+    // Nothing to do here
+    return;
+  }
+  if (change.removed.length === 1 && change.removed[0] === '') {
+    // Nothing removed
+    // Check whether first inserted character is newline
+    if (change.text.length > 1 && change.text[0] === '') {
+      // and first subsequent character is newline
+      let trailingLine = base[change.to.line];
+      if (trailingLine.length > change.to.ch && trailingLine[change.to.ch] === '\n') {
+        // Match, shift newline from head to tail
+        change.from.line += 1;
+        change.from.ch = 0;
+        change.text.push(change.text.shift()!);
+      }
+    }
+  } else if (change.text.length === 1 && change.text[0] === '') {
+    // Nothing added
+    // Check whether first removed character is newline
+    if (change.removed.length > 1 && change.removed[0] === '') {
+      // and first subsequent character is newline
+      let trailingLine = base[change.to.line];
+      if (trailingLine.length > change.to.ch && trailingLine[change.to.ch] === '\n') {
+        // Match, shift newline from head to tail
+        change.from.line += 1;
+        change.from.ch = 0;
+        change.to.line += 1;
+        change.to.ch = 0;
+        change.removed.push(change.removed.shift()!);
+      }
+    }
+  } else {
+    // Both added and removed
+    // Check whether first removed character is newline
+    if (change.removed.length > 1 && change.removed[0] === '') {
+      // and first subsequent character is newline
+      let trailingLine = base[change.to.line];
+      if (trailingLine.length > change.to.ch && trailingLine[change.to.ch] === '\n') {
+        // Match, shift newline from head to tail
+        change.from.line += 1;
+        change.from.ch = 0;
+        change.to.line += 1;
+        change.to.ch = 0;
+        change.text.push(change.text.shift()!);
+        change.removed.push(change.removed.shift()!);
+      }
+    }
+  }
+}
+
 export
 function updateModel(options: IUpdateModelOptions) {
   let model = options.model;