[oil-language] Expression errors produce error status 3 in a command.

So then errexit can take over.  This fixes uncaught IndexError,
KeyError, ZeroDivisionError, etc.

We still don't have a good story for TypeError.  There is a one-off
around one EvalExpr.

Addresses #942.

core/error.py

@@ -181,3 +181,6 @@ class ErrExit(FatalRuntime):
 
     Travels between WordEvaluator and CommandEvaluator.
     """
+
+  class Expr(FatalRuntime):
+    """ e.g. KeyError, IndexError, ZeroDivisionError """

cpp/core_error.h

@@ -145,6 +145,19 @@ class ErrExit : public _ErrorWithLocation {
   }
 };
 
+// Stub: the parts that raise aren't translated
+class Expr : public _ErrorWithLocation {
+#if 0
+ public:
+  Expr(Str* user_str, int span_id)
+      : _ErrorWithLocation(user_str, span_id) {
+  }
+  Expr(Str* user_str, Token* token)
+      : _ErrorWithLocation(user_str, token) {
+  }
+#endif
+};
+
 // Stub
 class Runtime : public _ErrorWithLocation {
  public:

cpp/frontend_flag_spec.cc

@@ -292,7 +292,8 @@ Tuple2<args::_Attributes*, args::Reader*> ParseCmdVal(
 
 // With optional arg
 Tuple2<args::_Attributes*, args::Reader*> ParseCmdVal(
-    Str* spec_name, runtime_asdl::cmd_value__Argv* cmd_val, bool accept_typed_args) {
+    Str* spec_name, runtime_asdl::cmd_value__Argv* cmd_val,
+    bool accept_typed_args) {
   // TODO: disallow typed args!
   ParseCmdVal(spec_name, cmd_val);
 }

cpp/frontend_flag_spec.h

@@ -122,7 +122,8 @@ Tuple2<args::_Attributes*, args::Reader*> ParseCmdVal(
 
 // With optional arg
 Tuple2<args::_Attributes*, args::Reader*> ParseCmdVal(
-    Str* spec_name, runtime_asdl::cmd_value__Argv* cmd_val, bool accept_typed_args);
+    Str* spec_name, runtime_asdl::cmd_value__Argv* cmd_val,
+    bool accept_typed_args);
 
 Tuple2<args::_Attributes*, args::Reader*> ParseLikeEcho(
     Str* spec_name, runtime_asdl::cmd_value__Argv* cmd_val);

doc/error-handling.md

@@ -429,14 +429,16 @@ the rules for Oil's new command types:
 - `proc`.  As with defining shell functions, defining a `proc` never fails.  It
   always exits `0`.
 - `var`, `const`, `setvar`, and the `_` keyword.  If an exception occurs during
-  expression evaluation, the status is `1`.  Otherwise it's `0`.
+  expression evaluation, the status is `3`.  Otherwise it's `0`.
 
 Similarly, an expression sub like like `echo $[1 / 0]` will raise an internal
-exception, and the status of `echo` will be `1`.  (This is similar to what
+exception, and the status of `echo` will be `3`.  (This is similar to what
 happens when a redirect fails.)
-
-TODO: implement these rules.  Maybe consider status 3?
 
+Note: The status `3` is an arbitrary non-zero status that's not used by other
+shells.  Status `2` is generally for syntax errors and status `1` is for most
+runtime failures.
+
 ## Summary
 
 Oil uses three mechanisms to fix error handling once and for all.

oil_lang/expr_eval.py

@@ -13,6 +13,7 @@
     lvalue, value, value_e, scope_e,
 )
 from asdl import runtime
+from core import error
 from core.pyerror import e_die, log
 from frontend import consts
 from oil_lang import objects
@@ -311,9 +312,13 @@ def EvalExpr(self, node):
       if node.op.id == Id.Arith_Star:
         return left * right
       if node.op.id == Id.Arith_Slash:
-        # NOTE: from __future__ import division changes 5/2!
-        # But just make it explicit.
-        return float(left) / right  # floating point division
+        # NOTE: does not depend on from __future__ import division
+        try:
+          result = float(left) / right  # floating point division
+        except ZeroDivisionError:
+          raise error.Expr('divide by zero', token=node.op)
+
+        return result
 
       if node.op.id == Id.Expr_DSlash:
         return left // right  # integer divison
@@ -554,7 +559,16 @@ def _gen():
     if node.tag == expr_e.Subscript:
       obj = self.EvalExpr(node.obj)
       index = self._EvalIndices(node.indices)
-      return obj[index]
+      try:
+        result = obj[index]
+      except KeyError:
+        # TODO: expr.Subscript has no error location
+        raise error.Expr('dict entry not found', span_id=runtime.NO_SPID)
+      except IndexError:
+        # TODO: expr.Subscript has no error location
+        raise error.Expr('index out of range', span_id=runtime.NO_SPID)
+
+      return result
 
     # Note: This is only for the obj.method() case.  We will probably change
     # the AST and get rid of getattr().
@@ -568,7 +582,12 @@ def _gen():
 
       if id_ == Id.Expr_RArrow:  # d->key is like d['key']
         name = node.attr.val
-        return o[name]
+        try:
+          result = o[name]
+        except KeyError:
+          raise error.Expr('dict entry not found', token=node.op)
+
+        return result
 
       if id_ == Id.Expr_DColon:  # StaticName::member
         raise NotImplementedError(id_)

osh/cmd_eval.py

@@ -1403,6 +1403,9 @@ def _Execute(self, node):
             try:
               status = self._Dispatch(node, cmd_st)
               check_errexit = cmd_st.check_errexit
+            except error.Expr as e:
+              self.errfmt.PrettyPrintError(e, prefix='expression: ')
+              status = 3
             except error.FailGlob as e:
               if not e.HasLocation():  # Last resort!
                 e.span_id = self.mem.CurrentSpanId()

spec/fatal-errors.test.sh

@@ -0,0 +1,186 @@
+#
+# Some shell errors are unrecoverable!  Like divide by zero (except in bash.
+#
+# Any others?
+
+
+#### Unrecoverable: divide by zero in redirect word
+
+$SH -c '
+echo hi > file$(( 42 / 0 )) in
+echo inside=$?
+'
+echo outside=$?
+
+## STDOUT:
+outside=1
+## END
+
+## OK dash/ash STDOUT:
+outside=2
+## END
+
+# bash makes the command fail
+## OK bash STDOUT:
+inside=1
+outside=0
+## END:
+
+
+#### Unrecoverable: divide by zero in conditional word
+
+$SH -c '
+if test foo$(( 42 / 0 )) = foo; then
+  echo true
+else
+  echo false
+fi
+echo inside=$?
+'
+echo outside=$?
+
+echo ---
+
+$SH -c '
+if test foo$(( 42 / 0 )) = foo; then
+  echo true
+fi
+echo inside=$?
+'
+echo outside=$?
+
+## STDOUT:
+outside=1
+---
+outside=1
+## END
+
+## OK dash/ash STDOUT:
+outside=2
+---
+outside=2
+## END
+
+# bash makes the command fail
+## OK bash STDOUT:
+inside=1
+outside=0
+---
+inside=1
+outside=0
+## END:
+
+# weird difference in zsh!
+
+## BUG zsh STDOUT:
+outside=1
+---
+outside=0
+## END
+
+
+#### Unrecoverable: divide by zero in case
+
+$SH -c '
+case $(( 42 / 0 )) in
+  (*) echo hi ;;
+esac
+echo inside=$?
+'
+echo outside=$?
+
+echo ---
+
+$SH -c '
+case foo in
+  ( $(( 42 / 0 )) )
+    echo hi
+    ;;
+esac
+echo inside=$?
+'
+echo outside=$?
+
+## STDOUT:
+outside=1
+---
+outside=1
+## END
+
+## OK dash/ash STDOUT:
+outside=2
+---
+outside=2
+## END
+
+## OK bash STDOUT:
+inside=1
+outside=0
+---
+inside=1
+outside=0
+## END:
+
+## BUG zsh STDOUT:
+outside=0
+---
+outside=0
+## END
+
+
+#### Unrecoverable: ${undef?message}
+
+$SH -c '
+echo ${undef?message}
+echo inside=$?
+'
+echo outside=$?
+
+$SH -c '
+case ${undef?message} in 
+  (*) echo hi ;;
+esac
+echo inside=$?
+'
+echo outside=$?
+
+## STDOUT:
+outside=1
+outside=1
+## END
+## OK dash STDOUT:
+outside=2
+outside=2
+## END
+## OK bash STDOUT:
+outside=127
+outside=127
+## END
+
+#### ${undef} with nounset
+
+$SH -c '
+set -o nounset
+case ${undef} in 
+  (*) echo hi ;;
+esac
+echo inside=$?
+'
+echo outside=$?
+
+## STDOUT:
+outside=1
+## END
+
+## OK dash STDOUT:
+outside=2
+## END
+
+## OK bash STDOUT:
+outside=127
+## END
+
+## BUG zsh STDOUT:
+outside=0
+## END
+

spec/oil-builtin-error.test.sh

@@ -227,13 +227,57 @@ process sub failed: 2 2
 ## END
 
 #### try can handled failed var, setvar, etc.
+shopt --set parse_brace
 
 try {
+  echo hi
   var x = 1 / 0
+  echo 'should not get here'
+}
+echo div $_status
+
+try {
+  var a = []
+  setvar item = a[1]
+  echo 'should not get here'
+}
+echo index $_status
+
+try {
+  var d = {}
+  setvar item = d['mykey']
+  echo 'should not get here'
+}
+echo key $_status
+
+try {
+  setvar item = d->mykey
+  echo 'should not get here'
+}
+echo arrow $_status
+
+## STDOUT:
+hi
+div 3
+index 3
+key 3
+arrow 3
+## END
+
+#### try can handled failed expr sub
+shopt --set parse_brace
+
+try {
+  echo hi
+
+  var d = {}
+  echo "result = $[d->BAD]"
+  echo 'should not get here'
 }
 echo _status=$_status
 ## STDOUT:
-_status=1
+hi
+_status=3
 ## END
 
 #### boolstatus with external command