Fixed PHP syntax highlighting outside <?php ?>

Previously, PHP syntax highlighting worked only inside <?php ... ?> block.

This commit adds specific check, and if user wants to highlight PHP code, special lexer is used, which highlights PHP code even without the <?php ... ?> block.

tildes/tildes/lib/markdown.py

@@ -13,7 +13,7 @@ from html5lib.filters.base import Filter
 from html5lib.treewalkers.base import NonRecursiveTreeWalker
 from pygments import highlight
 from pygments.formatters import HtmlFormatter
-from pygments.lexers import get_lexer_by_name
+from pygments.lexers import get_lexer_by_name, PhpLexer
 from pygments.util import ClassNotFound
 
 from tildes.metrics import histogram_timer
@@ -206,7 +206,13 @@ def apply_syntax_highlighting(html: str) -> str:
         language = code_block["class"][0].replace("language-", "")
 
         try:
-            lexer = get_lexer_by_name(language)
+            # If target language is PHP, override default lexer construction
+            # and set startinline to True, so even code that is not enclosed
+            # inside <?php ... ?> will get highlighted.
+            if language in ["php", "php3", "php4", "php5"]:
+                lexer = PhpLexer(startinline=True)
+            else:
+                lexer = get_lexer_by_name(language)
         except ClassNotFound:
             continue