Slight refactoring to share logic between echo -e and $''.

core/lexer.py

@@ -256,6 +256,7 @@ def Tokens(self, line):
       if not matches:
         raise AssertionError(
             'no match at position %d: %r (%r)' % (pos, line, line[pos]))
+      # NOTE: Need longest-match semantics to find \377 vs \.
       end_pos, tok_type, tok_val = max(matches, key=lambda m: m[0])
       yield tok_type, line[pos:end_pos]
       pos = end_pos

osh/lex.py

@@ -405,6 +405,10 @@ def IsKeyword(name):
 
   # Backslash that ends a line.  Note '.' doesn't match a newline character.
   C('\\\n', Id.Char_Literals),
+
+  # e.g. \A is not an escape, and \x doesn't match a hex escape.  This could be
+  # an error.
+  C('\\', Id.Char_Literals),
 ]
 
 # Used by ECHO_LEXER in core/builtin.py.
@@ -415,12 +419,6 @@ def IsKeyword(name):
 
   C(r'\c', Id.Char_Stop),
 
-  # e.g. \A -> \A, is not a backslash escape.
-  # This has to come AFTER the \c and so forth.
-  #
-  # This includes embedded \n?  Is that possible with echo -e?
-  R(r'\\.', Id.Char_Literals),
-
   # Backslash that ends the string.
   R(r'\\$', Id.Char_Literals),
 
@@ -443,9 +441,6 @@ def IsKeyword(name):
   # well.
   R(r"[^\\'\0]+", Id.Char_Literals),
 
-  # e.g. \x doesn't match a hex escape.  This could be an error.
-  C('\\', Id.Char_Literals),
-
   C("'", Id.Right_SingleQuote),
 
   # Backslash that ends the file!  Caught by re2c exhaustiveness check.  Parser