1310045 - incorrect error when accidentally using the destructuring operator

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Pomax]

I was trying to use the destructuring operator but did not notice that the following ES7 syntax is not supported yet:

  ({a, b, ...rest} = {a:1, b:2, c:3, d:4});

However, the JS error this throws seems to be based on "what the engine is doing" rather than being based on the code the user wrote:

  SyntaxError: invalid property id

There is no "id" in the code I wrote, so the expected error is more something like "SyntaxError: unexpected token '...'" or a similarly indicative notice that lets the user figure out that Firefox is tripping up over the "..." syntax.

Comment 1

[Jeff Walden [:Waldo]]

The error message here could perhaps be better -- but also, if we have the right developer UI, it shouldn't *need* to be, because it should include location information from SpiderMonkey.  This location information is certainly present, and it's definitely calculated correctly, because our JS shell displays that information quite correctly:

js>  ({a, b, ...rest} = {a:1, b:2, c:3, d:4});
typein:1:9 SyntaxError: invalid property id:
typein:1:9  ({a, b, ...rest} = {a:1, b:2, c:3, d:4});
typein:1:9 .........^

What developer UI are you using?  It may be worth filing a bug against something else to more clearly expose that location, in addition to crafting a better error message here.

As to this error: it looks like this is trivially fixed by modifying the |default| case in Parser.cpp's |Parser<ParseHandler>::propertyName|.  The proper change is likely something along the lines of reporting an error using JSMSG_UNEXPECTED_TOKEN, with the exact code looking something similar to how the other uses of that error number look.

Comment 2

[Pomax]

This is just in the plain Firefox dev tools "console" tab.

Comment 3

[Tooru Fujisawa [:arai]]

unfortunately, devtools console doesn't show location information for console input :/
at least it should show line/column

Comment 4

[Tooru Fujisawa [:arai]]

filed bug 1315242 for devtools console part.

Comment 5

[Cosm]

I want to work on this bug.

Comment 6

[Cosm]

Attachment: patch.txt

Comment 7

[Jeff Walden [:Waldo]]

Comment on attachment 8807935 [details] [diff] [review]
patch.txt

Review of attachment 8807935 [details] [diff] [review]:
-----------------------------------------------------------------

Looks good.  Do you need someone to land this for you?

Comment 8

[Jeff Walden [:Waldo]]

(IRC conversation says the answer is yes.  I've rebased the patch on tip and queued it up for landing, the next time I'm landing stuff.)

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/2b7949845f17
When a non-property-name token is observed instead of a property name in an object/class literal or destructuring pattern, indicate the unexpected token the way most unexpected tokens are indicated using JSMSG_UNEXPECTED_TOKEN.  r=jwalden

Comment 10

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/2b7949845f17