Fix editor markdown not incrementing in a numbered list (#33187)

Amended the logic for newPrefix in the MarkdownEditor to resolve
incorrect number ordering.

Fixes #33184

Attached screenshot of fixed input similar to issue 
<img width="175" alt="Screenshot 2025-01-09 at 23 59 24"
src="https://github.com/user-attachments/assets/dfa23cf1-f3db-4b5e-99d2-a71bbcb289a8"
/>

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/features/comp/EditorMarkdown.test.ts

@@ -1,4 +1,166 @@
-import {initTextareaMarkdown} from './EditorMarkdown.ts';
+import {initTextareaMarkdown, markdownHandleIndention, textareaSplitLines} from './EditorMarkdown.ts';
+
+test('textareaSplitLines', () => {
+  let ret = textareaSplitLines('a\nbc\nd', 0);
+  expect(ret).toEqual({lines: ['a', 'bc', 'd'], lengthBeforePosLine: 0, posLineIndex: 0, inlinePos: 0});
+
+  ret = textareaSplitLines('a\nbc\nd', 1);
+  expect(ret).toEqual({lines: ['a', 'bc', 'd'], lengthBeforePosLine: 0, posLineIndex: 0, inlinePos: 1});
+
+  ret = textareaSplitLines('a\nbc\nd', 2);
+  expect(ret).toEqual({lines: ['a', 'bc', 'd'], lengthBeforePosLine: 2, posLineIndex: 1, inlinePos: 0});
+
+  ret = textareaSplitLines('a\nbc\nd', 3);
+  expect(ret).toEqual({lines: ['a', 'bc', 'd'], lengthBeforePosLine: 2, posLineIndex: 1, inlinePos: 1});
+
+  ret = textareaSplitLines('a\nbc\nd', 4);
+  expect(ret).toEqual({lines: ['a', 'bc', 'd'], lengthBeforePosLine: 2, posLineIndex: 1, inlinePos: 2});
+
+  ret = textareaSplitLines('a\nbc\nd', 5);
+  expect(ret).toEqual({lines: ['a', 'bc', 'd'], lengthBeforePosLine: 5, posLineIndex: 2, inlinePos: 0});
+
+  ret = textareaSplitLines('a\nbc\nd', 6);
+  expect(ret).toEqual({lines: ['a', 'bc', 'd'], lengthBeforePosLine: 5, posLineIndex: 2, inlinePos: 1});
+});
+
+test('markdownHandleIndention', () => {
+  const testInput = (input: string, expected?: string) => {
+    const inputPos = input.indexOf('|');
+    input = input.replace('|', '');
+    const ret = markdownHandleIndention({value: input, selStart: inputPos, selEnd: inputPos});
+    if (expected === null) {
+      expect(ret).toEqual({handled: false});
+    } else {
+      const expectedPos = expected.indexOf('|');
+      expected = expected.replace('|', '');
+      expect(ret).toEqual({
+        handled: true,
+        valueSelection: {value: expected, selStart: expectedPos, selEnd: expectedPos},
+      });
+    }
+  };
+
+  testInput(`
+  a|b
+`, `
+  a
+  |b
+`);
+
+  testInput(`
+1. a
+2. |
+`, `
+1. a
+|
+`);
+
+  testInput(`
+|1. a
+`, null); // let browser handle it
+
+  testInput(`
+1. a
+1. b|c
+`, `
+1. a
+2. b
+3. |c
+`);
+
+  testInput(`
+2. a
+2. b|
+
+1. x
+1. y
+`, `
+1. a
+2. b
+3. |
+
+1. x
+1. y
+`);
+
+  testInput(`
+2. a
+2. b
+
+1. x|
+1. y
+`, `
+2. a
+2. b
+
+1. x
+2. |
+3. y
+`);
+
+  testInput(`
+1. a
+2. b|
+3. c
+`, `
+1. a
+2. b
+3. |
+4. c
+`);
+
+  testInput(`
+1. a
+  1. b
+  2. b
+  3. b
+  4. b
+1. c|
+`, `
+1. a
+  1. b
+  2. b
+  3. b
+  4. b
+2. c
+3. |
+`);
+
+  testInput(`
+1. a
+2. a
+3. a
+4. a
+5. a
+6. a
+7. a
+8. a
+9. b|c
+`, `
+1. a
+2. a
+3. a
+4. a
+5. a
+6. a
+7. a
+8. a
+9. b
+10. |c
+`);
+
+  // this is a special case, it's difficult to re-format the parent level at the moment, so leave it to the future
+  testInput(`
+1. a
+  2. b|
+3. c
+`, `
+1. a
+  1. b
+  2. |
+3. c
+`);
+});
 
 test('EditorMarkdown', () => {
   const textarea = document.createElement('textarea');
@@ -32,10 +194,10 @@ test('EditorMarkdown', () => {
   testInput({value: '1. \n2. ', pos: 3}, {value: '\n2. ', pos: 0});
 
   testInput('- x', '- x\n- ');
-  testInput('1. foo', '1. foo\n1. ');
-  testInput({value: '1. a\n2. b\n3. c', pos: 4}, {value: '1. a\n1. \n2. b\n3. c', pos: 8});
+  testInput('1. foo', '1. foo\n2. ');
+  testInput({value: '1. a\n2. b\n3. c', pos: 4}, {value: '1. a\n2. \n3. b\n4. c', pos: 8});
   testInput('- [ ]', '- [ ]\n- ');
   testInput('- [ ] foo', '- [ ] foo\n- [ ] ');
   testInput('* [x] foo', '* [x] foo\n* [ ] ');
-  testInput('1. [x] foo', '1. [x] foo\n1. [ ] ');
+  testInput('1. [x] foo', '1. [x] foo\n2. [ ] ');
 });