tools: Let python_syntax tool show errors.

- Wasn't worth treating python specially.

eris/tools.py

@@ -3,7 +3,6 @@
 # Copyright (C) 2015-2019 Andrew Hamilton. All rights reserved.
 # Licensed under the Artistic License 2.0.
 
-import ast
 import contextlib
 import enum
 import functools
@@ -256,19 +255,6 @@ def contents(path):
     return Status.normal, text
 
 
-@deps(url="https://en.wikipedia.org/wiki/Python_syntax_and_semantics")
-def python_syntax(path):
-    with open(path) as f:
-        source = f.read()
-    try:
-        ast.parse(source)
-    except SyntaxError:
-        is_correct = False
-    else:
-        is_correct = True
-    return (Status.ok if is_correct else Status.problem), ""
-
-
 def _has_shebang_line(path):
     with open(path, "rb") as file_:
         return file_.read(2) == b"#!"

eris/tools.toml

@@ -46,6 +46,11 @@ tools_for_extensions = [
    ]
 
 
+[python_syntax]
+  dependencies = []
+  url = "https://en.wikipedia.org/wiki/Python_syntax_and_semantics"
+  command = "python3.7 -m py_compile"
+
 [pycodestyle]
   dependencies = ["pip/pycodestyle"]
   url = "http://pycodestyle.pycqa.org/en/latest/"