Fix Code mobject wrong indentation (#2725)

Author: nyabkun

manim/mobject/text/code_mobject.py

@@ -404,6 +404,11 @@ def _gen_code_json(self):
         # print(self.default_color,self.background_color)
         for i in range(3, -1, -1):
             self.html_string = self.html_string.replace("</" + " " * i, "</")
+
+        # handle pygments bug
+        # https://github.com/pygments/pygments/issues/961
+        self.html_string = self.html_string.replace("<span></span>", "")
+
         for i in range(10, -1, -1):
             self.html_string = self.html_string.replace(
                 "</span>" + " " * i,

tests/test_code_mobject.py

@@ -0,0 +1,15 @@
+from manim.mobject.text.code_mobject import Code
+
+
+def test_code_indentation():
+    co = Code(
+        code="""\
+    def test()
+        print("Hi")
+        """,
+        language="Python",
+        indentation_chars="    ",
+    )
+
+    assert co.tab_spaces[0] == 1
+    assert co.tab_spaces[1] == 2