[Issue 15293] File().byLine().map!toUpper throws UnicodeException at src\rt\util\utf.d(290): invalid UTF-8 sequence on pure ASCII file

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15293

--- Comment #5 from ag0aep6g at gmail.com ---
Reduced further:
----
static import std.file;
import std.stdio: File, writeln;

void main()
{
    std.file.write("gen.txt", "a\n\naa");

    auto file = File("gen.txt");
    char[] buffer;
    char[] line;

    file.readln(buffer, '\n');

    line = buffer;
    file.readln(line, '\n');

    line = buffer;
    file.readln(line, '\n');

    writeln(line.capacity); /* "0" */
    writeln(line[0 .. 1].capacity); /* "255" -- nonsense */
}
----

This reminds me more and more of issue 13856.

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