Fix mangling of characters below 0xFF

NEWS.rst

@@ -34,6 +34,7 @@ Bug Fixes
 * Fixed errors from `from __future__ import ...` statements and missing Hy
   module docstrings caused by automatic importing of Hy builtins.
 * Fixed crash in `mangle` for some pathological inputs
+* Fixed incorrect mangling of some characters at low code points
 
 0.15.0
 ==============================

hy/lex/__init__.py

@@ -61,7 +61,10 @@ def mangle(s):
     according to Hy's mangling rules."""
     def unicode_char_to_hex(uchr):
         # Covert a unicode char to hex string, without prefix
-        return uchr.encode('unicode-escape').decode('utf-8').lstrip('\\U').lstrip('\\u').lstrip('0')
+        if len(uchr) == 1 and ord(uchr) < 128:
+            return format(ord(uchr), 'x')
+        return (uchr.encode('unicode-escape').decode('utf-8')
+            .lstrip('\\U').lstrip('\\u').lstrip('\\x').lstrip('0'))
 
     assert s
 

tests/native_tests/mangling.hy

@@ -158,6 +158,27 @@
     (assert (= (mangle a) b))
     (assert (= (unmangle b) a))))
 
+
+(defn test-nongraphic []
+  ; https://github.com/hylang/hy/issues/1694
+
+  (assert (= (mangle " ") "hyx_XspaceX"))
+  (assert (= (mangle "\a") "hyx_XU7X"))
+  (assert (= (mangle "\t") "hyx_XU9X"))
+  (assert (= (mangle "\n") "hyx_XUaX"))
+  (assert (= (mangle "\r") "hyx_XUdX"))
+  (assert (= (mangle "\r") "hyx_XUdX"))
+
+  (setv c (try unichr (except [NameError] chr)))
+  (assert (= (mangle (c 127)) "hyx_XU7fX"))
+  (assert (= (mangle (c 128)) "hyx_XU80X"))
+  (assert (= (mangle (c 0xa0)) "hyx_XnoHbreak_spaceX"))
+  (assert (= (mangle (c 0x378)) "hyx_XU378X"))
+  (assert (= (mangle (c 0x200a) "hyx_Xhair_spaceX")))
+  (assert (= (mangle (c 0x2065)) "hyx_XU2065X"))
+  (assert (= (mangle (c 0x1000c)) "hyx_XU1000cX")))
+
+
 (defn test-mangle-bad-indent []
   ; Shouldn't crash with IndentationError
   (mangle "  0\n 0"))