Tidying up Syntax.guess_lexer, adding test

rich/syntax.py

@@ -322,8 +322,12 @@ def from_path(
 
     @classmethod
     def guess_lexer(cls, path: AnyStr, code: Optional[str] = None) -> str:
-        """Guess the name of the Pygments lexer to use based on path and optional string of code.
-        Initially looks at file extension and falls back to analysing the code, if supplied.
+        """Guess the alias of the Pygments lexer to use based on a path and an optional string of code.
+        If code is supplied, it will use a combination of the code and the filename to determine the
+        best lexer to use. For example, if the file is ``index.html`` and the file contains Django
+        templating syntax, then "html+django" will be returned. If the file is ``index.html``, and no
+        templating language is used, the "html" lexer will be used. If no string of code
+        is supplied, the lexer will be chosen based on the file extension..
 
         Args:
              path (AnyStr): The path to the file containing the code you wish to know the lexer for.
@@ -333,21 +337,29 @@ def guess_lexer(cls, path: AnyStr, code: Optional[str] = None) -> str:
         Returns:
             str: The name of the Pygments lexer that best matches the supplied path/code.
         """
-        lexer = None
+        lexer: Optional[Lexer] = None
         lexer_name = "default"
-        try:
-            _, ext = os.path.splitext(path)
-            if ext:
-                extension = ext.lstrip(".").lower()
-                lexer = get_lexer_by_name(extension)
-                lexer_name = lexer.name
-        except ClassNotFound:
-            pass
-        if code and lexer is None:
+        if code:
             try:
-                lexer_name = guess_lexer_for_filename(path, code).name
+                lexer: Lexer = guess_lexer_for_filename(path, code)
             except ClassNotFound:
                 pass
+
+        if not lexer:
+            try:
+                _, ext = os.path.splitext(path)
+                if ext:
+                    extension = ext.lstrip(".").lower()
+                    lexer = get_lexer_by_name(extension)
+            except ClassNotFound:
+                pass
+
+        if lexer:
+            if lexer.aliases:
+                lexer_name = lexer.aliases[0]
+            else:
+                lexer_name = lexer.name
+
         return lexer_name
 
     def _get_base_style(self) -> Style:

tests/test_syntax.py

@@ -1,17 +1,17 @@
 # coding=utf-8
 
+import os
 import sys
-import os, tempfile
+import tempfile
 
 import pytest
-from .render import render
+from pygments.lexers import PythonLexer
 
 from rich.panel import Panel
 from rich.style import Style
-from rich.syntax import Syntax, ANSISyntaxTheme, PygmentsSyntaxTheme, Color, Console
-
-from pygments.lexers import PythonLexer
+from rich.syntax import ANSISyntaxTheme, Color, Console, PygmentsSyntaxTheme, Syntax
 
+from .render import render
 
 CODE = '''\
 def loop_first_last(values: Iterable[T]) -> Iterable[Tuple[bool, bool, T]]:
@@ -266,6 +266,13 @@ def test_from_file_unknown_lexer():
         os.remove(path)
 
 
+def test_syntax_guess_lexer():
+    assert Syntax.guess_lexer("banana.py", "import this") == "python"
+    assert Syntax.guess_lexer("banana.html", "<a href='#'>hello</a>") == "html"
+    assert Syntax.guess_lexer("banana.html", "<%= @foo %>") == "rhtml"
+    assert Syntax.guess_lexer("banana.html", "{{something|filter:3}}") == "html+django"
+
+
 if __name__ == "__main__":
     syntax = Panel.fit(
         Syntax(