Re: lily: fix some type conversion warnings (issue 557190043 by address@hidden)

[hanwenn]

On 2020/01/23 20:02:58, Dan Eble wrote:
> On 2020/01/22 10:18:48, hanwenn wrote:
> > alternately, we could just do -Wno-conversion in the makefile, and
we wouldn't
> > have to do any work here at all.
> 
> These warnings weren't implemented just to irritate us.  They were
implemented
> because C is the basement of C++ and there are bugs hiding in its dark
corners.

That is a beautiful metaphor, but can you be a little more concrete? The
integer conversion
is the same between C and C++, and the warnings are applied to all C
code. That doesn't mean
that our C code would has the same kind of problems, and that the impact
of those problems
warrant investment to address them.

I mean, if we were writing a new SSL library, I surely would want
scrutiny on every cast, but
we aren't.

In LilyPond, the bulk of the warnings come from unsigned 64 bit sizes,
ie. vector and list sizes.

In order to cause an error, you would have to create vector or list of
over 2G of 
elements (on 32 bit architecture), so the unsigned size would be
converted to a negative integer. Since our objects 
are all larger than a single byte, there isn't enough memory for this to
be possible. (The same holds for 64 bit, 
except that you can't buy machines with that much RAM)

Similarly, for causing a problem by converting 64-bit size_t to a 32-bit
int, you'd have to create something 
with a size of over 2e9. What kind of score do you have in mind that
would cause this problem?

> My answer would be different if this were one of those categories of
warnings
> with a significant number of false positives, but it isn't, as far as
I've seen.

Can you point me to a conversion warning in LilyPond which could cause a
genuine, user-visible problem?


https://codereview.appspot.com/557190043/