Re: [PATCH v2 1/6] midx: add MIDX_PROGRESS flag <snip>

From: William Baker <williamtbakeremail@gmail.com>
Date: Oct 8, 2019, 16:24 UTC
Message-ID: <202ed2c5-9729-120f-fa0e-cee9ecec3b77@gmail.com>
In-Reply-To: <xmqqk19fn9jp.fsf@gitster-ct.c.googlers.com>

On 10/7/19 9:30 PM, Junio C Hamano wrote:

Show 33 quoted lines

> SZEDER Gábor <szeder.dev@gmail.com> writes:
> 
>>> 		func(PROGRESS | REGRESS);
>>> 		func(PROGRESS + REGRESS);
>>> 		func(PROGRESS * 3);
>>> 	}
>>>
>>> how caller came about to give 3?
>>
>> No, they tend to show (PROGRESS | REGRESS), at least both gdb and lldb
>> do.
> 
> OK.
> 
>>  If the enum has only constants with power-of-two values, then that
>> is the right way to write it, and the other two are asking for trouble
> 
> If the programmer and the debugger knows the constants are used to
> represent bits that can be or'ed together, what you say is correct,
> but that is entirely irrelevant.
> 
> What I was worried about is that the constants that are used to
> represent something that are *NOT* set of bits (hence "PROGRESS * 3"
> may be perfectly a reasonable thing for such an application) may be
> mistaken by an overly clever debugger and "3" may end up getting
> shown as "PROGRESS | REGRESS".  When there are only two constants
> (PROGRESS=1 and REGRESS=2), we humans nor debuggers can tell if that
> is to represent two bits that can be or'ed together, or it is an
> enumeration.
> 
> Until we gain the third constant, that is, at which time the third
> one may likely be 3 (if enumeration) or 4 (if bits).
>

I tried to see how lldb would handle the "PROGRESS * 3" scenario but I was unable to get lldb to display the "PROGRESS | REGRESS" format even when ORing the flags:

(lldb) l 399
   399 		enum test_flags {
   400 			TEST_FLAG_1 = 1 << 0,
   401 			TEST_FLAG_2 = 1 << 1,
   402 		};
   403 		
   404 		enum test_flags flags_1 = TEST_FLAG_1;
   405 		enum test_flags flags_2 = TEST_FLAG_2;
   406 		enum test_flags flags_both = TEST_FLAG_1 | TEST_FLAG_2;
   407 		
   408 		if (flags_1 || flags_2 || flags_both)
(lldb) p flags_1
(test_flags) $0 = TEST_FLAG_1
(lldb) p flags_2
(test_flags) $1 = TEST_FLAG_2
(lldb) p flags_both
(test_flags) $2 = 3
(lldb) fr v flags_both
(test_flags) flags_both = 3
(lldb) fr v --format enum flags_both
(test_flags) flags_both = 3
(lldb) version
lldb-902.0.79.7
  Swift-4.1

Is there something that needs to be adjusted in the config or with --format to display "TEST_FLAG_1 | TEST_FLAG_2" in this example?

Thanks, William