193700 - Useless error message when retrieving property of undefined object

Status: VERIFIED FIXED

(Rhino Graveyard :: Core, defect)

Description

[Russell Gold]

User-Agent:       Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)
Build Identifier: 

When parsing an expression like:

base.something.here, if "base.something" is undefined, the error message 
generated is "The undefined object has no properties" which is not very helpful 
in tracking down the problem.

The following patch should provide a better message:

RCS 
file: /cvsroot/mozilla/js/rhino/src/org/mozilla/javascript/Interpreter.java,v
retrieving revision 1.130
diff -u -r1.130 Interpreter.java
--- js/rhino/src/org/mozilla/javascript/Interpreter.java        17 Feb 2003 
08:50:55 -0000      1.130
+++ js/rhino/src/org/mozilla/javascript/Interpreter.java        17 Feb 2003 
15:07:46 -0000
@@ -2032,6 +2032,12 @@
         --stackTop;
         Object lhs = stack[stackTop];
         if (lhs == DBL_MRK) lhs = doubleWrap(sDbl[stackTop]);
+        else if (lhs == undefined) {
+            // special code for better error message for get property from 
undefined
+            int i = getShort(iCode, pc-6);
+            if (i != -1) lhs=strings[i];
+                throw NativeGlobal.typeError1( "msg.is.not.defined", 
ScriptRuntime.toString(lhs),scope );
+        }
         stack[stackTop] = ScriptRuntime.getProp(lhs, name, scope);
         break;
     }

Reproducible: Always

Steps to Reproduce:
1. Ask Rhino to parse an expression in which the second-to-last element part is 
undefined
2.
3.

Actual Results:  
It generates the above error message

Comment 1

[Russell Gold]

The submitted patch does not always work...  this one may be better:

Index: js/rhino/src/org/mozilla/javascript/Interpreter.java
===================================================================
RCS 
file: /cvsroot/mozilla/js/rhino/src/org/mozilla/javascript/Interpreter.java,v
retrieving revision 1.130
diff -u -r1.130 Interpreter.java
--- js/rhino/src/org/mozilla/javascript/Interpreter.java        17 Feb 2003 
08:50:55 -0000      1.130
+++ js/rhino/src/org/mozilla/javascript/Interpreter.java        17 Feb 2003 
15:43:53 -0000
@@ -2032,6 +2032,16 @@
         --stackTop;
         Object lhs = stack[stackTop];
         if (lhs == DBL_MRK) lhs = doubleWrap(sDbl[stackTop]);
+        else if (lhs == undefined) {
+            // special code for better error message for get property from 
undefined
+            int j = pc-6;
+            while (j > 0 && iCode[j] != 0) j--;
+            int i = getShort(iCode, j);
+            if (i >= 0 && i < strings.length) {
+                lhs=strings[i];
+                throw NativeGlobal.typeError1( "msg.is.not.defined", 
ScriptRuntime.toString(lhs),scope );
+            }
+        }
         stack[stackTop] = ScriptRuntime.getProp(lhs, name, scope);
         break;
     }

Comment 2

[Phil Schwartau]

cc'ing Igor to consider this patch -

Comment 3

[Igor Bukanov]

Although the patch idea is fine, I think it would be better to report the
property name for undefined null value, i.e. in x.y.z with undefined y it would
be sufficient for debugging to report about accessing the property z of
undefined. In this way a reasonable message would be printed for x[0].z or x.y[0]. 

Comment 4

[Igor Bukanov]

Attachment: Use property names in error messages about accessing undefined or null

Patch adds to various getElem/getProp explicit checks for null/undefined and in
such cases report which property of null/undefined was accessed.

With the patch I have in Rhino shell:

js> x = {}
[object Object]
js> x.y.z
js: "<stdin>", line 2: uncaught JavaScript exception: TypeError: Cannot get
property "z" from undefined (<stdin>; line 2)
js> x[0].z
js: "<stdin>", line 3: uncaught JavaScript exception: TypeError: Cannot get
property "z" from undefined (<stdin>; line 3)
js> x.y[0]
js: "<stdin>", line 4: uncaught JavaScript exception: TypeError: Cannot get
property "0" from undefined (<stdin>; line 4)

Comment 5

[Igor Bukanov]

Attachment: Patch update to report assignments to properties of undefined/null

This is a patch extention to cover property assignments as well so I have in
Rhino shell:

js> x={}
[object Object]
js> x.y.z
js: "<stdin>", line 2: uncaught JavaScript exception: TypeError: Cannot read
property "z" from undefined (<stdin>; line 2)
js> x.y.z=1
js: "<stdin>", line 3: uncaught JavaScript exception: TypeError: Cannot set
property "z" of undefined to "1" (<stdin>; line 3)
js> x.y[0]=Math.sin
js: "<stdin>", line 4: uncaught JavaScript exception: TypeError: Cannot set
property "0" of undefined to "org.mozilla.javascript.IdFunction@93dcd"
(<stdin>; line 4)
js> x[1][2]=1
js: "<stdin>", line 6: uncaught JavaScript exception: TypeError: Cannot set
property "2" of undefined to "1" (<stdin>; line 6)

Comment 6

[Igor Bukanov]

I commited the patch few days ago.

Comment 7

[Phil Schwartau]

Verified Fixed -

js> x = {}
[object Object]

js> x.y.z
js: "<stdin>", line 8: uncaught JavaScript exception: TypeError: Cannot read
property "z" from undefined (<stdin>; line 8)

js> x.y.z=1
js: "<stdin>", line 9: uncaught JavaScript exception: TypeError: Cannot set
property "z" of undefined to "1" (<stdin>; line 9

js> x.y[0]=Math.sin
js: "<stdin>", line 10: uncaught JavaScript exception: TypeError: Cannot set
property "0" of undefined to "org.mozilla.javasc
ipt.IdFunction@1f14ceb" (<stdin>; line 10)

js> x[1][2]=1
js: "<stdin>", line 11: uncaught JavaScript exception: TypeError: Cannot set
property "2" of undefined to "1" (<stdin>; line 1)

Comment 8

[Igor Bukanov]

Targeting as resolved against 1.5R5