bpo-38870: correctly escape unprintable characters on ast.unparse (GH-20166)

i64 · pablogsal · isidentical · web-flow · commit d71a6492dbd5 · 2020-05-18T19:41:35.000+01:00
Unprintable characters such as `\x00` weren't correctly roundtripped
due to not using default string repr when generating docstrings. This
patch correctly encodes all unprintable characters (except `\n` and `\t`, which
are commonly used for formatting, and found unescaped).

Co-authored-by: Pablo Galindo &lt;Pablogsal@gmail.com&gt;
Co-authored-by: Batuhan Taskaya &lt;isidentical@gmail.com&gt;
diff --git a/Lib/ast.py b/Lib/ast.py
@@ -1090,18 +1090,26 @@ def visit_Name(self, node):
         self.write(node.id)
 
     def _write_docstring(self, node):
+        def esc_char(c):
+            if c in ("\n", "\t"):
+                # In the AST form, we don't know the author's intentation
+                # about how this should be displayed. We'll only escape
+                # \n and \t, because they are more likely to be unescaped
+                # in the source
+                return c
+            return c.encode('unicode_escape').decode('ascii')
+
         self.fill()
         if node.kind == "u":
             self.write("u")
 
         value = node.value
         if value:
             # Preserve quotes in the docstring by escaping them
-            value = value.replace("\\", "\\\\")
-            value = value.replace('"""', '""\"')
-            value = value.replace("\r", "\\r")
+            value = "".join(map(esc_char, value))
             if value[-1] == '"':
                 value = value.replace('"', '\\"', -1)
+            value = value.replace('"""', '""\\"')
 
         self.write(f'"""{value}"""')
 
diff --git a/Lib/test/test_unparse.py b/Lib/test/test_unparse.py
@@ -324,7 +324,11 @@ def test_docstrings(self):
             '\\t',
             '\n',
             '\\n',
-            '\r\\r\t\\t\n\\n'
+            '\r\\r\t\\t\n\\n',
+            '""">>> content = \"\"\"blabla\"\"\" <<<"""',
+            r'foo\n\x00',
+            '🐍⛎𩸽üéş^\X\BB\N{LONG RIGHTWARDS SQUIGGLE ARROW}'
+
         )
         for docstring in docstrings:
             # check as Module docstrings for easy testing
