fix: preformatted content being re-formatted (#376)

The issue had to do with how Firefox handles pasting newlines inside a <pre
contenteditable> tag (TinyMCE's editor works via contenteditable) and
fast-xml-parser's parsing. In Firefox, newlines are converted to <br> when
pasted, while Chrome preserves them. The parser by default trims spaces in text
nodes. In Firefox, the parser creates individual text nodes between the <br>
elements, and those have leading spaces in the example. In Chrome, there are no
<br> elements and the entire content is a single text node as-is. Setting
trimValues to false disables the trimming and resolves this issue in Firefox.

While investigating this, I noticed the builder also mishandles <br /> tags
emitted by the editor, converting them to <br></br>. The unpairedTags option in
the builder ensures they are output correctly as a single tag, and setting
suppressUnpairedNode to false ensures that single tag is <br/> rather than <br>
to remain XML compatible.

While trying to resolve this, I was looking into the paste plugin in TinyMCE.
It changes the behavior of pasting, making it more consistent between Chrome
and Firefox (i.e. both emit <br>) and is incorporated into TinyMCE 6 core.
Unfortunately, it seems to mangle pasting inside a <pre> tag by inserting
redundant nbsp characters (tinymce/tinymce#9017). TinyMCE 6 also outputs <br>
rather than <br /> - adding unpairedTags to the parser options is meant to
handle this, but it does not seem to behave entirely correct
(NaturalIntelligence/fast-xml-parser#609). These should be kept in mind if/when
upgrading to TinyMCE 6 (the different behaviors can be seen easily at
https://fiddle.tiny.cloud).

src/editors/containers/ProblemEditor/data/ReactStateOLXParser.js

@@ -13,17 +13,26 @@ class ReactStateOLXParser {
         hex: false,
       },
       preserveOrder: true,
+      // Ensure whitespace inside <pre> tags is preserved
+      trimValues: false,
+      // Parse <br> correctly
+      unpairedTags: ['br'],
     };
     const richTextBuilderOptions = {
       ignoreAttributes: false,
       attributeNamePrefix: '@_',
       suppressBooleanAttributes: false,
-      format: true,
+      // Avoid formatting as it adds unwanted newlines and whitespace,
+      // breaking <pre> tags
+      format: false,
       numberParseOptions: {
         leadingZeros: false,
         hex: false,
       },
       preserveOrder: true,
+      unpairedTags: ['br'],
+      // Output <br/> rather than <br>
+      suppressUnpairedNode: false,
     };
 
     this.richTextParser = new XMLParser(richTextParserOptions);

src/editors/containers/ProblemEditor/data/ReactStateOLXParser.test.js

@@ -104,5 +104,15 @@ describe('Check React State OLXParser problem', () => {
       const buildOLX = stateParser.buildOLX();
       expect(buildOLX.replace(/\s/g, '')).toEqual(numberParseTestOLX.buildOLX.replace(/\s/g, ''));
     });
+    test('correctly preserves whitespace inside pre tags', () => {
+      const stateParser = new ReactStateOLXParser({
+        problem: { problemType: 'optionresponse', answers: [] },
+        editorObject: { question: '<pre>  1  a<br />  2  b<br /></pre>', hints: [] },
+      });
+      const buildOLX = stateParser.buildOLX();
+      expect(buildOLX).toEqual(
+        '<problem><optionresponse>\n<pre>  1  a<br/>  2  b<br/></pre><optioninput></optioninput></optionresponse>\n</problem>',
+      );
+    });
   });
 });