Underscore cannot be defined more than once in proc

[Wh1teDuke]

Test

proc foo(_, _: int) = discard

Expected
Compiles with no issue. It works for one underscore, though I'm not sure this is even a feature.

Got

Test.nim(1, 13) Error: attempt to redefine: '_'

---

>nim -v
Nim Compiler Version 1.1.1 [Linux: i386]
Compiled at 2020-02-19
Copyright (c) 2006-2019 by Andreas Rumpf

git hash: 8c22518d673cf792fa064d2d561d1c6f03b823bb
active boot switches: -d:release

[ringabout]

Maybe this works as expected?

error: redefinition of parameter '_'
 N_LIB_PRIVATE N_NIMCALL(void, foo__BOpZ9bkFh9cyFk2iF9aui4mXw)(NI _, NI windx, NI _);

If the _ isn't mangled, it is natural to cause this result.

Maybe this needs to be documented instead of being fixed?

[timotheecour]

for consistency with (EDIT) #15972, IMO proc foo(_, _: int) = discard should be allowed.
Would avoid having to use dummy names eg in:
proc bar(a: int, fun: proc(_: int, _: float)) = discard

[ringabout]

@timotheecour
Wrong RFC link.

If mangling underscore names is more consistent, I will try that.

[timotheecour]

@xflywind thx, fixed link

[ringabout]

Because JS backend mangles function parameters, it does work in JS backend and VM.

proc foo(_, _: int) = echo "123"

foo(1, 2)

function foo_385875969(__385875971, __385875972) {
  rawEcho(makeNimstrLit("123"));
}
foo_385875969(1, 2);

[timotheecour]

this should probably be legal:

proc foo(_, _: int) = discard

this should not be legal:

proc main(_: int) = echo _

see also nim-lang/RFCs#292 which defines a useful use case for passing _; that use case should be reserved