[expr_eval] Add type checking for list indexing.

Fixes a spec test.

osh/expr_eval.py

@@ -380,6 +380,10 @@ def Eval(self, node, int_coerce=True):
       int for Str
       List[int] for StrArray
       Dict[str, str] for AssocArray (TODO: Should we support this?)
+
+    NOTE: (( A['x'] = 'x' )) and (( x = A['x'] )) are syntactically valid in
+    bash, but don't do what you'd think.  'x' sometimes a variable name and
+    sometimes a key.
     """
     # OSH semantics: Variable NAMES cannot be formed dynamically; but INTEGERS
     # can.  ${foo:-3}4 is OK.  $? will be a compound word too, so we don't have
@@ -508,13 +512,16 @@ def Eval(self, node, int_coerce=True):
       if op_id == Id.Arith_LBracket:
         # StrArray or AssocArray
         if isinstance(lhs, list):
+          if not isinstance(rhs, int):
+            e_die('Expected index to be an integer, got %r', rhs)
           try:
             item = lhs[rhs]
           except IndexError:
             if self.exec_opts.nounset:
               e_die('Index out of bounds')
             else:
-              return 0  # If not fatal, return 0
+              # TODO: Should be None for Undef instead?  Or ''?
+              return 0
 
         elif isinstance(lhs, dict):
           try:
@@ -523,7 +530,8 @@ def Eval(self, node, int_coerce=True):
             if self.exec_opts.nounset:
               e_die('Invalid key %r' % rhs)
             else:
-              return 0  # If not fatal, return 0
+              # TODO: Should be None for Undef instead?  Or ''?
+              return 0
         else:
           # TODO: Add error context
           e_die('Expected array in index expression, got %s', lhs)

osh/runtime.asdl

@@ -53,6 +53,7 @@ module runtime
   lvalue = 
     LhsName(string name)
   | LhsIndexedName(string name, int index)
+  | LhsStringKey(string name, string key)
 
   -- evaluated version of syntax.redir
   redirect = 

spec/array.test.sh

@@ -488,7 +488,9 @@ shopt -u strict-arith
 a=(1 2 3)
 (( x = a[a] ))
 echo $x
+## status: 1
 ## stdout-json: ""
+## BUG bash/mksh status: 0
 ## BUG bash/mksh STDOUT:
 2
 ## END

spec/dparen.test.sh

@@ -119,3 +119,16 @@ values = 0
 ## N-I zsh status: 1
 ## N-I mksh stdout-json: ""
 ## N-I mksh status: 1
+
+#### literal strings not properly supported
+declare -A A
+A['x']=x
+(( x = A['x'] ))
+(( A['y'] = 'y' ))  # y is a variable, gets coerced to 0
+echo $x ${A['y']}
+## STDOUT:
+0 0
+## END
+## N-I zsh/mksh STDOUT:
+0
+## END

test/spec.sh

@@ -554,7 +554,7 @@ arith-context() {
 }
 
 array() {
-  sh-spec spec/array.test.sh --osh-failures-allowed 3 \
+  sh-spec spec/array.test.sh --osh-failures-allowed 2 \
     $BASH $MKSH $OSH_LIST "$@"
 }
 
@@ -593,7 +593,7 @@ dbracket() {
 }
 
 dparen() {
-  sh-spec spec/dparen.test.sh --osh-failures-allowed 4 \
+  sh-spec spec/dparen.test.sh --osh-failures-allowed 5 \
     $BASH $MKSH $ZSH $OSH_LIST "$@"
 }