Render html tags inside img alt as their original text (#979)

Spec is not clear on how to handle this. Three variations exist:

```
$ echo '![text <textarea> text](image.png)' | /home/user/commonmark.js/bin/commonmark
<p><img src="image.png" alt="text <textarea> text" /></p>

$ echo '![text <textarea> text](image.png)' | /home/user/cmark/build/src/cmark
<p><img src="image.png" alt="text &lt;textarea&gt; text" /></p>

$ echo '![text <textarea> text](image.png)' | /home/user/.local/bin/commonmark
<p><img src="image.png" alt="text  text" /></p>
```

Prior to this commit:
 - when HTML tags are enabled, tags were removed (as in Haskell version)
 - when HTML tags are disabled, tags were escaped (as in C version)

After this commit:
 - tags will be escaped (as in C version) regardless of HTML flag

+ render hardbreaks as newlines, same as cmark

CHANGELOG.md

@@ -6,6 +6,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 
+## [14.0.0] - WIP
+### Fixed
+- Html tokens inside img alt are now rendered as their original text, #896.
+- Hardbreaks inside img alt are now rendered as newlines.
+
+
 ## [13.0.2] - 2023-09-26
 ### Security
 - Fixed crash/infinite loop caused by linkify inline rule, #957.

lib/renderer.mjs

@@ -268,12 +268,23 @@ Renderer.prototype.renderInlineAsText = function (tokens, options, env) {
   let result = ''
 
   for (let i = 0, len = tokens.length; i < len; i++) {
-    if (tokens[i].type === 'text') {
-      result += tokens[i].content
-    } else if (tokens[i].type === 'image') {
-      result += this.renderInlineAsText(tokens[i].children, options, env)
-    } else if (tokens[i].type === 'softbreak') {
-      result += '\n'
+    switch (tokens[i].type) {
+      case 'text':
+        result += tokens[i].content
+        break
+      case 'image':
+        result += this.renderInlineAsText(tokens[i].children, options, env)
+        break
+      case 'html_inline':
+      case 'html_block':
+        result += tokens[i].content
+        break
+      case 'softbreak':
+      case 'hardbreak':
+        result += '\n'
+        break
+      default:
+        // all other tokens are skipped
     }
   }
 

test/fixtures/markdown-it/commonmark_extras.txt

@@ -682,7 +682,7 @@ Issue #772. Header rule should not interfere with html tags.
 </pre>
 .
 
-Newline in image description
+Softbreak in image description
 .
 There is a newline in this image ![here
 it is](https://github.com/executablebooks/)
@@ -690,3 +690,19 @@ it is](https://github.com/executablebooks/)
 <p>There is a newline in this image <img src="https://github.com/executablebooks/" alt="here
 it is"></p>
 .
+
+Hardbreak in image description
+.
+There is a newline in this image ![here\
+it is](https://github.com/executablebooks/)
+.
+<p>There is a newline in this image <img src="https://github.com/executablebooks/" alt="here
+it is"></p>
+.
+
+Html in image description
+.
+![text <textarea> text](image.png)
+.
+<p><img src="image.png" alt="text &lt;textarea&gt; text"></p>
+.