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digitalmars.D.bugs - [Issue 1841] New: Closure detection doesn't work when variable is used in a nested function

reply d-bugmail puremagic.com writes:
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           Summary: Closure detection doesn't work when variable is used in
                    a nested function
           Product: D
           Version: 2.010
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: webmaster villagersonline.com


The following function should allocate the variable "heap" on the heap since it
is referenced in a delegate.  However, as you can tell from the output of the
program, it gets allocated on the stack instead.

CODE

import std.stdio;

void Foo(void delegate() ignored)
{
  int stack;
  int heap;
writefln("&stack=",&stack,"   &heap=",&heap);
writefln();


  void nested_func()
  {
    heap = 1;
  }


  Foo(delegate void() { nested_func(); });
}

void main()
{
  Foo(null);
}

END CODE


For comparison, if you modify the variable "heap" directly in the deletage
literal, instead of having the delegate literal call the nested function, then
"heap" is correctly allocated on the heap.

Interestingly, if you have *two* heap variables, one of which is modified
directly in the delegate literal, and the other of which is only modified
inside the nested function, then BOTH of the heap variables are on the heap. 
This seems to indicate that the compiler is doing a "do I need any closures
here" pass, which has a bug, and then has a "build closures" pass, which works
correctly.


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Feb 15 2008
next sibling parent d-bugmail puremagic.com writes:
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------- Comment #1 from webmaster villagersonline.com  2008-03-31 12:38 -------
This seems to work on dmd 2.012.  Did dmd change?


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Mar 31 2008
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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clugdbug yahoo.com.au


--- Comment #2 from Don <clugdbug yahoo.com.au> 2010-07-27 00:03:36 PDT ---
Here's a clearer test case. The second assert fails.

Closure detection works correctly if you change the delegate literal to:
  return delegate int() { int x=heap; return nested_func(); };

---------------------
//import std.stdio;

int delegate() Foo()
{
  int stack;
  int heap=3;
//  writeln("&stack=",&stack,"   &heap=",&heap);

  int nested_func()
  {
    ++heap;
    return heap;
  }
  return delegate int() { return nested_func(); };
}

void main()
{
  auto z = Foo();
  auto p = Foo();
  assert(z()==4); // OK
  p();
  assert(z()==5);  // fails
}

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--- Comment #3 from Don <clugdbug yahoo.com.au> 2010-10-19 23:56:53 PDT ---
See also bug 1908, test case 5w, for another example.

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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xinok live.com


--- Comment #4 from Don <clugdbug yahoo.com.au> 2012-03-27 23:23:03 PDT ---
*** Issue 7766 has been marked as a duplicate of this issue. ***

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Denis Shelomovskij <verylonglogin.reg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dpx.infinity gmail.com


--- Comment #5 from Denis Shelomovskij <verylonglogin.reg gmail.com> 2012-11-12
13:42:26 MSK ---
*** Issue 7303 has been marked as a duplicate of this issue. ***

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Denis Shelomovskij <verylonglogin.reg gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |verylonglogin.reg gmail.com
           Platform|x86                         |All
            Version|2.010                       |D2
         OS/Version|Linux                       |All
           Severity|normal                      |major


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--- Comment #6 from Don <clugdbug yahoo.com.au> 2013-01-24 01:23:08 PST ---
The basic problem is that the existing closure detection only checks parents of
nested functions. It should also check sibling nested functions.
Ie, if one nested function f calls another nested function g, then if g needs a
closure, then so does f.
More complex cases are possible, such as where f calls g which calls h, f
escapes, h uses closure variables but f and g don't.

I have a fix for the original test case, still working on the more complex
cases.

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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bdom.pub+deebugz gmail.com


--- Comment #7 from Don <clugdbug yahoo.com.au> 2013-01-26 02:22:04 PST ---
*** Issue 2148 has been marked as a duplicate of this issue. ***

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--- Comment #8 from github-bugzilla puremagic.com 2013-01-27 11:34:12 PST ---
Commit pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/e5de59d30026fa5267541a928d67af1e8c06f922
Fix issue 1841 Closure detection fails in nested functions

If an escaping function doesn't use any closure variables, but
calls another nested function which does, it must be marked as
needing a closure. This 'calling a sibling' case was missing.

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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla digitalmars.com
         Resolution|                            |FIXED


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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |edmccard verizon.net


--- Comment #9 from Don <clugdbug yahoo.com.au> 2013-02-01 00:51:02 PST ---
*** Issue 7801 has been marked as a duplicate of this issue. ***

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