[BUG] Closure state is stack allocated

[DayDun]

Bug Description

fn f(func: fn() -> None) -> fn() capturing -> None:
    fn wrapper():
        func()
    return wrapper

fn g():
    pass

f(g)()

crashes with

error: Execution was interrupted, reason: signal SIGSEGV: address not mapped to object (fault address: 0x0).
The process has been left at the point where it was interrupted, use "thread return -x" to return to the state before expression evaluation.

Expected behavior would be for it to not crash.

Note that making func a parameter instead does work

fn f[func: fn() -> None]() -> fn() capturing -> None:
    fn wrapper():
        func()
    return wrapper

fn g():
    pass

f[g]()()

Steps to Reproduce

Run the provided code.

Context

11:devices:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-poddc6801ca_838f_451d_8258_ad4fd3f41a6d.slice/cri-containerd-64526640c2bf917695ffc3502241083d511fa40e64ed25700e17bfdeb28e172c.scope
10:memory:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-poddc6801ca_838f_451d_8258_ad4fd3f41a6d.slice/cri-containerd-64526640c2bf917695ffc3502241083d511fa40e64ed25700e17bfdeb28e172c.scope
9:cpuset:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-poddc6801ca_838f_451d_8258_ad4fd3f41a6d.slice/cri-containerd-64526640c2bf917695ffc3502241083d511fa40e64ed25700e17bfdeb28e172c.scope
8:freezer:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-poddc6801ca_838f_451d_8258_ad4fd3f41a6d.slice/cri-containerd-64526640c2bf917695ffc3502241083d511fa40e64ed25700e17bfdeb28e172c.scope
7:net_cls,net_prio:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-poddc6801ca_838f_451d_8258_ad4fd3f41a6d.slice/cri-containerd-64526640c2bf917695ffc3502241083d511fa40e64ed25700e17bfdeb28e172c.scope
6:cpu,cpuacct:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-poddc6801ca_838f_451d_8258_ad4fd3f41a6d.slice/cri-containerd-64526640c2bf917695ffc3502241083d511fa40e64ed25700e17bfdeb28e172c.scope
5:pids:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-poddc6801ca_838f_451d_8258_ad4fd3f41a6d.slice/cri-containerd-64526640c2bf917695ffc3502241083d511fa40e64ed25700e17bfdeb28e172c.scope
4:blkio:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-poddc6801ca_838f_451d_8258_ad4fd3f41a6d.slice/cri-containerd-64526640c2bf917695ffc3502241083d511fa40e64ed25700e17bfdeb28e172c.scope
3:hugetlb:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-poddc6801ca_838f_451d_8258_ad4fd3f41a6d.slice/cri-containerd-64526640c2bf917695ffc3502241083d511fa40e64ed25700e17bfdeb28e172c.scope
2:perf_event:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-poddc6801ca_838f_451d_8258_ad4fd3f41a6d.slice/cri-containerd-64526640c2bf917695ffc3502241083d511fa40e64ed25700e17bfdeb28e172c.scope
1:name=systemd:/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-poddc6801ca_838f_451d_8258_ad4fd3f41a6d.slice/cri-containerd-64526640c2bf917695ffc3502241083d511fa40e64ed25700e17bfdeb28e172c.scope
0::/

[Mogball]

This is a known issue. Capture state is stack allocated. It should be heap allocated and it's something we plan to fix.

[Mogball]

This issue is observed here as well #111

[survuvi]

With the magic %%python the output of this closure is ok: x = 7, y = 4, z = 2, return: 13

%%python
def outer_func(x):
    y = 4
    def inner_func(z):
        print(f'x = {x}, y = {y}, z = {z}')
        return x + y + z
    return inner_func

closure = outer_func(7)
print(closure(2))  

But without:

def outer_func(x):
    y = 4
    def inner_func(z):
        print("x = ", x, " y = ",  y, " z = ", z)
        return x + y + z
    return inner_func

closure = outer_func(7)
print(closure(2))

_error: Expression [5]:10:14: no matching function in call to 'print':
print("x = ", x, " y = ", y, " z = ",z)
~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/.modular/Kernels/mojo/Stdlib/IO.mojo:244:1: candidate not viable: callee expects 0 arguments, but 6 were specified
fn print():
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:249:1: candidate not viable: callee expects 1 argument, but 6 were specified
fn print(t: DType):
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:258:1: candidate not viable: callee expects 1 argument, but 6 were specified
fn print(x: String):
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:268:1: candidate not viable: callee expects 1 argument, but 6 were specified
fn print(x: StringRef):
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:278:1: candidate not viable: callee expects 1 argument, but 6 were specified
fn print(x: StringLiteral):
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:287:1: candidate not viable: callee expects 1 argument, but 6 were specified
fn print(x: Bool):
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:296:1: candidate not viable: callee expects 1 argument, but 6 were specified
fn print(x: FloatLiteral):
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:305:1: candidate not viable: callee expects 1 argument, but 6 were specified
fn print(x: Int):
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:314:1: candidate not viable: callee expects 2 input parameters but 0 were provided
fn print[
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:339:1: candidate not viable: callee expects 1 input parameter but 0 were provided
fn print[type: DType](x: Atomic[type]):
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:352:1: candidate not viable: callee expects 1 input parameter but 0 were provided
fn print[length: Int](shape: DimList):
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:378:1: candidate not viable: callee expects 1 argument, but 6 were specified
fn print(obj: object):
^

/.modular/Kernels/mojo/Stdlib/IO.mojo:397:1: candidate not viable: argument #1 cannot be converted from 'object' to '_Printable'
fn print(*elements: _Printable):
^

error: Expression [5]:12:12: 'fn(object) raises capturing -> object' value cannot be converted to 'object' in return value
return inner_func_

[Manish0045]

from time import time
def greet():
i=0
for i in range(10):
time.sleep(1)
print(i)
print('Hello world!')
greet()
/ I got same error in the above code can anyone suggest what am I doing wrong in it.

[oskgo]

The following variant segfaults in the beta:

fn f(func: fn()-> None) -> fn() capturing -> None:
        fn wrapper():
            func()
        return wrapper

fn g():
    pass

def main():
    f(g)()

[ematejska]

@Mogball Stdlib or lang for labels?

[Mogball]

lang. Closures are a language issue

[emillma]

The following examples might be relevant.

fn outer(number: Int = 1) -> fn () capturing -> None:
    fn inner():
        print("inner=", number)  #prints  inner=94467979384400 (varies)
    print("outer=", number)  #prints  outer=1
    return inner

fn outer(number: Int = 1) -> fn () capturing -> None:
    print("outer=", number)  #prints  inner=1
    fn inner():
        print("inner=", number)  #prints inner=1
    print("outer=", number)  #prints  outer=1
    return inner

fn outer(number: Int = 1) -> fn () capturing -> None:
    print("outer=", number)  #SEGFAULT
    fn inner():
        print("inner=", number)  #SEGFAULT
    return inner

[oskgo]

@emillma Reproducing this behavior in the playground requires using print(number) rather than print("outer=", number)

[Brian-M-J]

I started a discussion (#1690) on why stack allocated closures may not necessarily be a "bug" to "fix". Tell me what you guys think.