Accept 'shopt -s expand_aliases' as a noop.

Add more spec test cases for alias.

core/state.py

@@ -154,6 +154,8 @@ def __init__(self, mem):
     # these.
     self.nullglob = False
     self.failglob = False
+    # No-op for bash compatibility.  We always expand aliases.
+    self.expand_aliases = False
 
     #
     # OSH-specific options that are not yet implemented.
@@ -251,7 +253,7 @@ def SetOption(self, opt_name, b):
         new_val = runtime.Str(':'.join(names))
         self.mem.InternalSetGlobal('SHELLOPTS', new_val)
 
-  SHOPT_OPTIONS = ('nullglob', 'failglob')
+  SHOPT_OPTIONS = ('nullglob', 'failglob', 'expand_aliases')
 
   def SetShoptOption(self, opt_name, b):
     """ For shopt -s/-u. """

spec/alias.test.sh

@@ -4,7 +4,7 @@
 #
 # http://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_03_01
 #
-# Bash is the only one that doesn't support aliases!
+# Bash is the only one that doesn't support aliases by default!
 
 #### Basic alias
 shopt -s expand_aliases  # bash requires this
@@ -18,6 +18,21 @@ hi
 expected failure
 ## END
 
+#### define and use alias on a single line
+shopt -s expand_aliases
+alias e=echo; e one  # this is not alias-expanded because we parse lines at once
+e two; e three
+## STDOUT:
+two
+three
+## END
+
+#### alias can override builtin
+shopt -s expand_aliases
+alias echo='echo foo'
+echo bar
+## stdout: foo bar
+
 #### defining multiple aliases, then unalias
 shopt -s expand_aliases  # bash requires this
 x=x