120157 - {}.a is an error, print({}.a) is not

Status: VERIFIED INVALID

(Core :: JavaScript Engine, defect)

Description

[timeless]

current-cvsbuild\mozilla\dist\WIN32_D.OBJ\bin>xpcshell.exe -s -w
js> a={};a.b
typein:1: strict warning: assignment to undeclared variable a
typein:1: strict warning: reference to undefined property a.b
js> {}.a
typein:2: syntax error:
typein:2: {}.a

typein:2: ..^
typein:2: SyntaxError: syntax error:
typein:2: {}.a

typein:2: ..^
js> print({}.a)
typein:3: strict warning: reference to undefined property {}.a
undefined

Comment 1

[Phil Schwartau]

Same thing in my SpiderMonkey shell. Isn' it odd we get TWO syntax errors:

[//d/JS_TRUNK/mozilla/js/src/WINNT4.0_DBG.OBJ] ./js -s -w

js> {}.a
4: syntax error:
4: {}.a
4: ..^
4: SyntaxError: syntax error:
4: {}.a
4: ..^


Whereas these all just give strict warnings: 

js> print({}.a);
5: strict warning: reference to undefined property {}.a
undefined

js> if ({}.a) {print('OK')}
6: strict warning: reference to undefined property {}.a

js> var x = {}.a;
7: strict warning: reference to undefined property {}.a


Note this:

js> typeof {}.a
undefined

js> {}.a == undefined
25: syntax error:
25: {}.a == undefined
25: ..^
25: SyntaxError: syntax error:
25: {}.a == undefined
25: ..^

Comment 2

[Phil Schwartau]

Reassigning to Kenton; cc'ing Brendan in case this is of interest -

Comment 3

[timeless]

oh yeah of course the reason i was playing with this at all was typeof :-).
Odd that i didn't notice the significance of the second syntax error (note: 
'syntax error:' and 'SyntaxError: syntax error:'

my guess about that is that the first one shouldn't be emitted and should be 
subsumed (?) by the second one.

otoh, perhaps this is expected behavior
>\build\mozilla\dist\WIN32_D.OBJ\bin\xpcshell.exe
js> /1
typein:1: unterminated regular expression literal:
typein:1: /1

typein:1: ^
typein:1: SyntaxError: unterminated regular expression literal:
typein:1: /1

typein:1: ^
odd, i wasn't trying to create a regular expression, i was trying to not take 
something and divide by 1. well, compiler knows best :)

Comment 4

[Brendan Eich [:brendan]]

This bug is invalid, and timeless should know better.  Unless you put {} in an
expression context (such as print's actual parameter, or in parens), it's a
block statement, not an object literal.

/be

Comment 5

[timeless]

i'll go hide under a rock now.  a new bug should be filed for syntax error 
outputting twice if that's a bug at all.

Comment 6

[Brendan Eich [:brendan]]

timeless: that double-report is a bug, due to a mess left behind when errors as
exceptions went in.  I have a patch.  Please file the bug on me, cc'ing khanson,
shaver, jband, and rogerl.  Thanks,

/be

Comment 7

[Phil Schwartau]

I have filed bug 120197 on the double-report issue.