[errors] Fix error location for arith_expr.VarRef.

This code path was tickled by ble.sh.

Addresses issue #664.

Also turn off warnings since they come up too much.  #598 to provide
strictness levels could help.

frontend/location.py

@@ -13,7 +13,7 @@
     command__DoGroup, command__BraceGroup, command__Subshell,
     command__WhileUntil, command__If, command__Case, command__TimeBlock,
 
-    arith_expr_e, arith_expr_t, arith_expr__ArithWord,
+    arith_expr_e, arith_expr_t, arith_expr__ArithWord, arith_expr__VarRef
 )
 from asdl import runtime
 from core.util import log
@@ -70,8 +70,8 @@ def SpanForArithExpr(node):
   UP_node = node
   with tagswitch(node) as case:
     if case(arith_expr_e.VarRef):
-      # TODO: VarRef should store a token instead of a string!
-      return runtime.NO_SPID
+      node = cast(arith_expr__VarRef, UP_node)
+      return node.token.span_id
     elif case(arith_expr_e.ArithWord):
       node = cast(arith_expr__ArithWord, UP_node)
       return word_.LeftMostSpanForWord(node.w)

osh/sh_expr_eval.py

@@ -363,7 +363,7 @@ def _ValToIntOrError(self, val, span_id=runtime.NO_SPID):
 
         elif case(value_e.Str):
           val = cast(value__Str, UP_val)
-          return _StringToInteger(val.s, span_id=span_id)  # calls e_die
+          return _StringToInteger(val.s, span_id=span_id)  # calls e_strict
 
         elif case(value_e.Obj):
           # Note: this handles var x = 42; echo $(( x > 2 )).
@@ -377,8 +377,6 @@ def _ValToIntOrError(self, val, span_id=runtime.NO_SPID):
       if self.exec_opts.strict_arith():
         raise
       else:
-        span_id = word_.SpanIdFromError(e)
-        self.errfmt.PrettyPrintError(e, prefix='warning: ')
         return 0
 
     # Arrays and associative arrays always fail -- not controlled by
@@ -744,7 +742,6 @@ def _StringToIntegerOrError(self, s, blame_word=None):
       if self.always_strict or self.exec_opts.strict_arith():
         raise
       else:
-        self.errfmt.PrettyPrintError(e, prefix='warning: ')
         i = 0
     return i