Issue with algorithm.fold - dmd hangs

[monkyyy]

On Friday, 4 April 2025 at 23:35:14 UTC, Borax Man wrote:
>
> Sorry if this is an actual bug with DMD.  I suspect it might 
> be, but I'm not sure whether the fault is DMD or my code.
>
> Short story, I wrote a program for work to do calculations for 
> my team in D, and use Windows 64bit DMD to compile.  I upgraded 
> to the latest DMD, and its hangs on compile.  I tried under 
> Linux, and same issue.
>
> Verison is
>
> DMD64 D Compiler v2.111.0
> Copyright (C) 1999-2025 by The D Language Foundation, All 
> Rights Reserved written by Walter Bright
>
> When I compile using dmd with the "-v" switch, these are the 
> last messages.
>
> import    
> core.internal.string	(/usr/include/dmd/druntime/import/core/internal/string.d)
> semantic3 foldtest
> import    std.utf	(/usr/include/dmd/phobos/std/utf.d)
> import    
> std.algorithm.internal	(/usr/include/dmd/phobos/std/algorithm/internal.d)
>
> It hangs at the last line, just stays there consuming CPU 
> cycles.
>
> I've extracted a minimal failing copy.  The line which calls 
> "fold" to sum the values causes it to hang.  This compiles fine 
> with GDC and LDC2, and worked with DMD version before 2.100 (I 
> didn't try anything between 2.100 and 2.111.0)
>
> Is my code wrong, or have I stumbled on a bug?
>
> Code below
>
> ==================================================
>
> import std.algorithm;
> import std.range;
> import std.stdio;
>
> final class DataClass {
> private:
> 	int x;
>
> 	this()
> 	{}
> 	this(in int _x)
> 	{
> 		x=_x;
> 	}
>
> 	auto ref opOpAssign(string op : "+")(in DataClass other)
> 	{
> 		x += other.x;
> 		return this;
> 	}
>
> 	void printx()
> 	{
> 		writeln(x);
> 	}
>
> 	auto opBinary(string op : "+")(in DataClass other)
> 	{
> 		DataClass newr = new DataClass();
> 		newr.x = x + other.x;
> 		return newr;
> 	}
> }
>
> int main()
> {
> 	DataClass[] dataclassarray;
> 	DataClass result = new DataClass();
> 	DataClass d1 = new DataClass(3);
> 	DataClass d2 = new DataClass(4);
> 	DataClass d3= new DataClass(10);
> 	DataClass d4 = new DataClass(12);
> 	DataClass res2 = new DataClass(10);
> 	dataclassarray~=d1;
> 	dataclassarray~=d2;
> 	dataclassarray~=d3;
> 	dataclassarray~=d4;
> 	res2 += d1; // This works
> 	res2.printx();
> 	res2 = d1 + d2; // This works
> 	res2.printx();
> 	result = dataclassarray.fold!((a,b) => a + b);  // This causes 
> dmd to hang.
> 	result.printx();
> 	return 0;
> }

works for me