Handle -1 from wcwidth (e.g. newline) (#402)

- Only try to find width of last line of prompt.
- Handle -1 from wcwidth by returning number of bytes in prompt.
- Does not handle newline inside of escape characters.

Addresses #394

- Add tests for control characters in prompt

See #402 (comment) and
#394 (comment) for
discussion.

core/comp_ui.py

@@ -32,7 +32,8 @@
 def _PromptLen(prompt_str):
   """Ignore all characters between \x01 and \x02 and handle unicode characters.
   In particular, the display width of a string may be different from either the
-  number of bytes or the number of unicode characters."""
+  number of bytes or the number of unicode characters.
+  Additionally, if there are multiple lines in the prompt, only give the length of the last line."""
   escaped = False
   display_str = ""
   for c in prompt_str:
@@ -42,11 +43,15 @@ def _PromptLen(prompt_str):
       escaped = False
     elif not escaped:
       display_str += c
+  last_line = display_str.split('\n')[-1]
   try:
-    return libc.wcswidth(display_str)
+    width = libc.wcswidth(last_line)
   # en_US.UTF-8 locale missing, just return the number of bytes
   except (SystemError, UnicodeError):
     return len(display_str)
+  if width == -1:
+    return len(display_str)
+  return width
 
 
 class PromptState(object):

core/comp_ui_test.py

@@ -165,6 +165,14 @@ def testValidEscapes(self):
         comp_ui._PromptLen("\x01\x02 hi \x01hi\x02 \x01\x02 hello"),
         len(" hi   hello"))
 
+  def testNewline(self):
+    self.assertEqual(comp_ui._PromptLen("\n"), 0)
+    self.assertEqual(comp_ui._PromptLen("abc\ndef"), 3)
+    self.assertEqual(comp_ui._PromptLen(""), 0)
+
+  def testControlCharacters(self):
+    self.assertEqual(comp_ui._PromptLen("\xef"), 1)
+    self.assertEqual(comp_ui._PromptLen("\x03\x05"), 2)
 
 if __name__ == '__main__':
   unittest.main()

native/libc_test.py

@@ -193,6 +193,7 @@ def testGetTerminalWidth(self):
   def testWcsWidth(self):
     self.assertEqual(1, libc.wcswidth("▶️"))
     self.assertEqual(28, libc.wcswidth("(osh) ~/.../unchanged/oil ▶️ "))
+    self.assertEqual(2, libc.wcswidth("→ "))
     self.assertRaises(UnicodeError, libc.wcswidth, "\xfe")
 
 if __name__ == '__main__':