[Issue 23976] std.range.slide fails in dmd-2.104.0

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23976

cbleser <cr at tagion.org> changed:

           What    |Removed                     |Added
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                 CC|                            |cr at tagion.org

--- Comment #1 from cbleser <cr at tagion.org> ---
Created attachment 1880
  --> https://issues.dlang.org/attachment.cgi?id=1880&action=edit
unittest which shows the bug


The bug occurs in the latest version dmd-2.104.0 but works in dmd-2.103.1 and
older.

The problem is when a slide(2) is taken of a rbtree range the last element
contains 1 element and not two.
But it only fails in combination with rbtree as far as I know.
The sample code is as follows.

```

import std.container.rbtree;
import std.range;
import std.stdio;
import std.algorithm;

struct RecycleSegment {
    int index;
//    uint size;
}
alias Indices = RedBlackTree!(RecycleSegment*, (a, b) => a.index < b.index); //
RecycleSegment: sorted by size.

unittest {

    const a=[17,42];
    writefln("%s", a.slide(2));
    // This passes for both dmd-2.103.1 and dmd-2.104.0
    assert(a.slide(2).map!(r => r.walkLength == 2).all);
    auto indices = new Indices;
    indices.insert(new RecycleSegment(42));
    indices.insert(new RecycleSegment(17));
    writefln("%s", indices[].slide(2));
    writefln("%s", indices[].slide(2).map!(r => r.walkLength == 2));
    // This passes in dmd-2.103.1 but fails in dmd-2.104.0
    assert(indices[].slide(2).map!(r => r.walkLength == 2).all);
}

```

This is the print out of dmd-1.103.1
```
[[17, 42]]
[[7F6E7F100020, 7F6E7F100010]]
[true]
```

And this is the print out of dmd-1.104.0 (Where it fails in the last assert)
```
[[17, 42]]
[[7F7622B00020, 7F7622B00010], [7F7622B00010]]
[true, false]
slide_bug.d(23): [unittest] unittest failure
```

As can be seen, the last slide has one element but it should not even be in the
new list.

But for some reason, it works with a simple array.

I hope this help to fix it.

Thanks.

--