bugdown: Add 'none' as alias for no syntax highlighting in codeblocks.

This is a precursor to #14404.

tools/setup/lang.json

@@ -31,6 +31,7 @@
     "matlab": 33,
     "mql": 9,
     "mql4": 9,
+    "none": 1,
     "objective-c": 35,
     "objectivec": 35,
     "objectpascal": 42,
@@ -38,6 +39,7 @@
     "perl": 40,
     "php": 44,
     "pl": 40,
+    "plain": 1,
     "prolog": 16,
     "python": 46,
     "quote": 50,
@@ -45,6 +47,7 @@
     "rb": 39,
     "ruby": 39,
     "rust": 8,
+    "text": 1,
     "sas": 30,
     "scala": 21,
     "scheme": 14,

zerver/lib/bugdown/fenced_code.py

@@ -165,6 +165,11 @@ def generic_handler(processor: Any, output: MutableSequence[str],
     else:
         return CodeHandler(processor, output, fence, lang, run_content_validators)
 
+def remap_language(lang: str) -> str:
+    if lang in ['none', 'noop', 'text', 'plain']:
+        return ''
+    return lang
+
 def check_for_new_fence(processor: Any, output: MutableSequence[str], line: str,
                         run_content_validators: Optional[bool]=False) -> None:
     m = FENCE_RE.match(line)
@@ -172,6 +177,8 @@ def check_for_new_fence(processor: Any, output: MutableSequence[str], line: str,
         fence = m.group('fence')
         lang = m.group('lang')
 
+        lang = remap_language(lang)
+
         handler = generic_handler(processor, output, fence, lang, run_content_validators)
         processor.push(handler)
     else:

zerver/tests/test_bugdown.py

@@ -119,6 +119,10 @@ class FencedBlockPreprocessorTest(TestCase):
             '```c#',
             'weirdchar()',
             '```',
+            '',
+            '``` none',
+            'no-highlight()',
+            '```',
             ''
         ]
         expected = [
@@ -133,6 +137,10 @@ class FencedBlockPreprocessorTest(TestCase):
             '',
             '**c#:weirdchar()**',
             '',
+            '',
+            '',
+            '**:no-highlight()**',
+            '',
             ''
         ]
         lines = processor.run(markdown)