[Issue 19335] New: std.getopt: make it an error to have options that differ only by case when case insensitive

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19335

          Issue ID: 19335
           Summary: std.getopt: make it an error to have options that
                    differ only by case when case insensitive
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: dhasenan at gmail.com

void main(string[] args)
{
    import std.getopt;
    import std.stdio;
    int a, A;
    getopt(args, "a", &a, "A", &A);
    writefln("a=%s, A=%s", a, A);
}

Compile, run with `-a 5 -A 10`.

The expected result is an exception saying that option `A|a` is multiply
defined, hopefully also mentioning that the case-sensitive flag exists.

The actual result is that `a` is set twice and `A` is not set.

This exception should also trigger when you define an argument named `H`.

(I would also argue that case-insensitive is a terrible default, but that's
unlikely to change.)

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