Chapel: Task Local Variables and File.reader() results in internal error

[LouisJenkinsCS]

var f = open("", iomode.rw);
forall i in 1..100 with (var reader = f.reader()) do ;

TIO

.code.tio.chpl:2: internal error: number of actuals does not match number of formals in reader() [resolution/lateConstCheck.cpp:139]

[bradcray]

@vasslitvinov: Any idea what's going on here?

[LouisJenkinsCS]

Perhaps this may help

var f = open("", iomode.rw);
coforall i in 1..100 with (var reader = f.reader()) do for i in 1..10 do;

TIO

internal error: unexpected intent in tiMarkForForallIntent() [passes/createTaskFunctions.cpp:155]

(Just so you don't miss coforall case)

[LouisJenkinsCS]

Also happens with begin.

[cassella]

Guessing it's the this arg, I was able to work around the forall compilation problem by adding a wrapping regular function,

proc getreader(f) { return f.reader(); }

var f = open("", iomode.rw);
forall i in 1..100 with (var reader = getreader(f)) do ;

That approach doesn't help the coforall.

[cassella]

Oh, oops. As @ben-albrecht and @bradcray noticed in #14386, the problem here has to do with f.reader() being a throws function, not with the this argument. My workaround "worked" as written only because the code being at implicit-module scope, the getreader() helper can call a throwing function without a try and without itself being throwing.

The error still happens when the non-method getreader() is marked throws in order to propagate f.reader()'s errors:

module foo {
  proc getreader(f) throws {
    return try f.reader();
  }

  var f = try! open("", iomode.rw);
  forall i in 1..100 with (var reader = getreader(f)) do ;
}

foo.chpl:8: internal error: number of actuals (2) does not match number of formals (3) in getreader() [resolution/lateConstCheck.cpp:139]

It can still be worked around in a non-prototype-module context by making getreader() dispose of any errors reader() throws:

module foo {
  proc getreader(f) {
    return try! f.reader();
  }

  var f = try! open("", iomode.rw);
  forall i in 1..100 with (var reader = getreader(f)) do ;
}

[vasslitvinov]

coforall i in 1..100 with (var reader = f.reader()) do for i in 1..10 do;

The compiler now reports "task-private variables are not supported for coforall/cobegin/begin".

Consider this an unimplemented feature.

[vasslitvinov]

14454 eliminates the internal error. However, it leaves unimplemented the case of non-POD task-private variables whose init expression throws. The compiler emits an error in this case.

As a workaround, wrap with try!, ex.:

forall i in 1..100 with (var reader = try! f.reader()) do ;

[bradcray]

@vasslitvinov: Is there a follow-on issue capturing the unimplemented feature of adding support for extending this support to non-POD types? If not, would you create one?

[vasslitvinov]

@bradcray I consider #9749 to be such an issue.