https://issues.dlang.org/show_bug.cgi?id=15215

          Issue ID: 15215
           Summary: Erroneous error messages in to!IntegralType
                    conversions
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: phobos
          Assignee: nobody@puremagic.com
          Reporter: samjnaa@gmail.com

Using DMD 2.068.2.

Code illustrating problem:

$ cat to_int_error_msg.d
import std.meta, std.conv, std.stdio;
void test(string num)
{
    writeln("Testing string: ", num);
    foreach(Type; AliasSeq!(ubyte, ushort, uint, ulong, byte, short, int,
long))
    {
        try to!Type(num);
        catch (ConvException e) writefln("to!%-6s : %s", Type.stringof, e.msg);
    }
    writeln();
}
void main() { foreach (num; ["2A", "-2A", "#2A"]) test(num); }

Output:

$ dmd -run to_int_error_msg.d
Testing string: 2A
to!ubyte  : Unexpected 'A' when converting from type string to type ubyte
to!ushort : Unexpected 'A' when converting from type string to type ushort
to!uint   : Unexpected 'A' when converting from type string to type uint
to!ulong  : Unexpected 'A' when converting from type string to type ulong
to!byte   : Unexpected 'A' when converting from type string to type byte
to!short  : Unexpected 'A' when converting from type string to type short
to!int    : Unexpected 'A' when converting from type string to type int
to!long   : Unexpected 'A' when converting from type string to type long

Testing string: -2A
to!ubyte  : Unexpected '2' when converting from type string to type uint
to!ushort : Unexpected '2' when converting from type string to type uint
to!uint   : Unexpected '2' when converting from type string to type uint
to!ulong  : Unexpected '2' when converting from type string to type ulong
to!byte   : Unexpected 'A' when converting from type string to type byte
to!short  : Unexpected 'A' when converting from type string to type short
to!int    : Unexpected 'A' when converting from type string to type int
to!long   : Unexpected 'A' when converting from type string to type long

Testing string: #2A
to!ubyte  : Unexpected '2' when converting from type string to type uint
to!ushort : Unexpected '2' when converting from type string to type uint
to!uint   : Unexpected '2' when converting from type string to type uint
to!ulong  : Unexpected '2' when converting from type string to type ulong
to!byte   : Unexpected '2' when converting from type string to type int
to!short  : Unexpected '2' when converting from type string to type int
to!int    : Unexpected '2' when converting from type string to type int
to!long   : Unexpected '2' when converting from type string to type long

Observations:

When input is 2A, error messages are fine.

When input is -2A, error messages are fine in case of signed types. In case of
unsigned types, there are two problems:
1) The message should flag the presence of "-" which is illegal in unsigned
types. It instead says "2" is unexpected.
2) The target type is wrongly mentioned as uint when it is actually ubyte or
ushort.

When input is #2A, error messages are not fine at all. The problems are:
1) Again, "2" is flagged as unexpected instead of "#".
2) The target type is wrongly mentioned as before, but now int is displayed for
byte and short too.

--