unsafeAddr broken in JS for proc parameters

[metagn]

Example

proc foo[T](x: T) = # generics doesn't matter here, you can try writing a proc for each type used below
  echo(unsafeAddr(x)[])

foo("hello")
foo(@[1, 2, 3])
foo([1, 2, 3])
foo(1)

import jsconsole

proc consoleFoo[T](x: T) =
  console.log(unsafeAddr(x)[])

consoleFoo("hello")
foo(@[1, 2, 3])
foo([1, 2, 3])
foo(1)

Current Output

@[]
[undefined, undefined, undefined]
undefined

1
1
undefined

Expected Output

"hello"
@[1, 2, 3]
[1, 2, 3]
1
"hello"
@[1, 2, 3]
[1, 2, 3]
1

Additional Information

• var x = x then addr fixes all of these. Simply adding let x = x also works.
• This was shown in Add ability to yield var's for iterators #3104 (comment) but the issue seems to be completely unrelated.
• Works fine for let & for variables.

$ nim -v
Nim Compiler Version 1.2.0

[bung87]

this was introduced in 61f2f1f

[ringabout]

this was introduced in 61f2f1f

No, I guess this never works, Nim v1.0.4 doesn't work too.

[bung87]

there's lot changes after v1.0.4, test agains it does not results "never works"

worked version maybe #15078

[ringabout]

In Nim 0.19.0

proc foo[T](x: T) = # generics doesn't matter here, you can try writing a proc for each type used below
  echo(unsafeAddr(x)[])

foo("hello")
foo(@[1, 2, 3])
foo([1, 2, 3])
foo(1)

gave:

@[]
D:\QQPCmgr\Desktop\Nim\nimcache\test.js:475
    throw new Error(cbuf_15801);
    ^

Error: Error: unhandled exception: index out of bounds [IndexError]
Traceback (most recent call last)
foo.foo, line: 2
$.$, line: 3486
collectionToString.collectionToString, line: 2176

    at unhandledException (D:\QQPCmgr\Desktop\Nim\nimcache\test.js:475:11)
    at raiseException (D:\QQPCmgr\Desktop\Nim\nimcache\test.js:264:3)
    at raiseIndexError (D:\QQPCmgr\Desktop\Nim\nimcache\test.js:490:3)
    at chckIndx (D:\QQPCmgr\Desktop\Nim\nimcache\test.js:284:3)
    at collection_to_string_25683 (D:\QQPCmgr\Desktop\Nim\nimcache\test.js:645:29)
    at HEX24_25674 (D:\QQPCmgr\Desktop\Nim\nimcache\test.js:683:32)
    at foo_25666 (D:\QQPCmgr\Desktop\Nim\nimcache\test.js:694:11)
    at Object.<anonymous> (D:\QQPCmgr\Desktop\Nim\nimcache\test.js:711:1)
    at Module._compile (internal/modules/cjs/loader.js:1200:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1220:10)
Error: execution of an external program failed: 'E:\node\node.exe D:\QQPCmgr\Desktop\Nim\nimcache\test.js '

[metagn]

I don't think there's really a way for this to be "introduced", this is very special behavior that the compiler must account for that I haven't seen implemented. You would have to track whether a proc uses unsafeAddr for a parameter, then generate the function signature differently depending on it. I think doing that would be dumb, a better way would be to disallow it (which I know we do a lot, but here it makes sense) and tell the user to use a ptr T parameter instead.