1275240 - Redeclaration of formal parameter with lexical binding should be SyntaxError

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Tooru Fujisawa [:arai]]

|function f(a) { let a }| should throw SyntaxError, but we throw TypeError

js> function f(a) { let a }
typein:1:20 TypeError: redeclaration of formal parameter a:
typein:1:20 function f(a) { let a }
typein:1:20 ....................^

https://tc39.github.io/ecma262/#sec-function-definitions-static-semantics-early-errors
>  * It is a Syntax Error if any element of the BoundNames of FormalParameters also occurs in the LexicallyDeclaredNames of FunctionBody.

Comment 1

[Tooru Fujisawa [:arai]]

Now testing the patch
  https://treeherder.mozilla.org/#/jobs?repo=try&revision=cf6a34839cbc

so far, single test fails
  https://dxr.mozilla.org/mozilla-central/source/js/src/tests/js1_8_1/regress/regress-452498-092.js

Comment 2

[Florian Scholz (Open Web Docs)]

fwiw, with strict mode warnings, this code also throws a TypeError warning and not a SyntaxError warning:
  function f(arg) { var arg } 

TypeError: variable arg redeclares argument 

That's JSMSG_VAR_HIDES_ARG and it appears quite often according to current Telemetry data.

Comment 3

[Tooru Fujisawa [:arai]]

(In reply to Florian Scholz [:fscholz] (MDN) from comment #2)
> fwiw, with strict mode warnings, this code also throws a TypeError warning
> and not a SyntaxError warning:
>   function f(arg) { var arg } 
> 
> TypeError: variable arg redeclares argument 
> 
> That's JSMSG_VAR_HIDES_ARG and it appears quite often according to current
> Telemetry data.

redeclaration with "var" is different thing than let/const.
not sure if that warning is specced thing.
will check it :)

Comment 4

[Tooru Fujisawa [:arai]]

the type of warning is not specced, so at least JSMSG_VAR_HIDES_ARG is not something we should change its type here.

Comment 5

[Tooru Fujisawa [:arai]]

Attachment: Fix the type of parameter redeclaration from TypeError to SyntaxError. r=shu

got r+ed via IRC

Comment 6

[Tooru Fujisawa [:arai]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/97d4fa9f099b14a98d4242f1c73507beb1f70081
Bug 1275240 - Fix the type of parameter redeclaration from TypeError to SyntaxError. r=shu

Comment 7

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/97d4fa9f099b

Comment 8

[Florian Scholz (Open Web Docs)]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Redeclared_parameter