[Issue 19856] New: [aApplycd2]: foreach (int) doesn't work on BigEndian targets

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19856

          Issue ID: 19856
           Summary: [aApplycd2]: foreach (int) doesn't work on BigEndian
                    targets
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: ibuclaw at gdcproject.org

In the following code, the index `i` is always zero.
---
void checkChars(ref string s) @safe pure
{
    dchar c;
    int n = -1;
    foreach (int i, dchar d; s)
    {
        if (!isChar(d))
        {
            c = d;
            n = i;
            break;
        }
    }
}
---

This is because the foreach body is delegatized, and the internal runtime
function passed it a size_t*.

The fix of course is to use ptrdiff_t for the index type instead, however, the
compiler should warn/error about such code.

There's already a deprecation path for other kinds of arrays, char/dchar/wchar
seems to have been forgotten when fixing issue 16976.

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