Merge pull request #680 from Textualize/css-syntax-error-message

Improve error message for CSS syntax error

sandbox/darren/just_a_box.css

@@ -4,7 +4,7 @@ Screen {
 
 #left_pane {
     background: red;
-    width: 20;
+    width: 20
     overflow: scroll scroll;
 }
 

src/textual/css/tokenizer.py

@@ -12,6 +12,7 @@ import rich.repr
 from rich.syntax import Syntax
 from rich.text import Text
 
+from ._error_tools import friendly_list
 from .._loop import loop_last
 
 
@@ -203,11 +204,13 @@ class Tokenizer:
         line = self.lines[line_no]
         match = expect.match(line, col_no)
         if match is None:
+            expected = friendly_list(" ".join(name.split("_")) for name in expect.names)
+            message = f"Expected one of {expected}.; Did you forget a semicolon at the end of a line?"
             raise TokenError(
                 self.path,
                 self.code,
                 (line_no, col_no),
-                "expected " + ", ".join(name.upper() for name in expect.names),
+                message,
             )
         iter_groups = iter(match.groups())
         next(iter_groups)