Conditions in loops processed as AssignmentExpression, should be Expression

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Per the standard, the condition in loops is an Expression, but Espruino evidently parses it as AssignmentExpression, disallowing the comma operator. This is particularly painful contexts like

while (x = costlyAccessor(i++), p(x.a, x.b)) …;

Minimal reproduction:

>while(0,0);
Uncaught SyntaxError: Got ',' expected ')'
 at line 1 col 8
while(0,0);
       ^
>for(;0,0;);
Uncaught SyntaxError: Got ',' expected ';'
 at line 1 col 7
for(;0,0;);
      ^
>do;while(0,0);
Uncaught SyntaxError: Got ',' expected ')'
 at line 1 col 11
do;while(0,0);

Oddly, if and switch have no such problem.

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Robin in reply to @stephenPspackman

Fri 2021.10.15

'Per the standard, the condition in loops is an Expression,'

Hi @user135362 when challenging referencing an outside document, providing the link to that document will assist us all in evaluating your concern.

As I see it:

The conditional expression for a while statement must evaluate true or false.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/while

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comma_Operator

http://www.espruino.com/Features

while https://262.ecma-international.org/5.1/#sec-12.6.2

In the sample provided x = costlyAccessor(i++) will always evaluate TRUE based on the truthy rules. Result: endless loop

https://www.sitepoint.com/javascript-truthy-falsy/

Also, >while(0,0); can never evalute TRUE. Result: never executes

So, as I see it, and as none of the references I have just found make any mention of using the comma operator within a while conditional, seems problematic.

Could be other reasons, but I'm sure this will open up to others for discussion. . . .

Conditions in loops processed as AssignmentExpression, should be Expression

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