[lldb-dev] LLDB Evolution - Final Form

[Zachary Turner via lldb-dev]

Well, but StringRef for example is well documented.  So it seems to me like
there's an example of a perfectly used assert.  It's documented that you
can't use null, and if you do it asserts.  Just like strlen.

The issue I have with "you can't ever assert" is that it brings it into an
absolute when it really shouldn't be.  We already agreed (I think) that
certain things that are well documented can assert.  But when we talk in
absolutes, it tends to sway people that they should always do that thing,
even when it's not the most appropriate solution.  And I think some of that
shows in the LLDB codebase where you've got hugely complicated logic that
is very hard to follow, reason about, or test, because no assumptions are
ever made about any of the inputs.  Even when they are internal inputs that
are entirely controlled by us.

On Tue, Sep 20, 2016 at 2:19 PM Greg Clayton <gclayton at apple.com> wrote:

> Again, strlen is a stupid example as it is well documented. All of llvm
> and clang are not.
> > On Sep 20, 2016, at 1:59 PM, Zachary Turner <zturner at google.com> wrote:
> >
> >
> >
> > On Tue, Sep 20, 2016 at 1:55 PM Greg Clayton <gclayton at apple.com> wrote:
> >
> > > On Sep 20, 2016, at 1:45 PM, Zachary Turner <zturner at google.com>
> wrote:
> > >
> > > I do agree that asserts are sometimes used improperly.  But who's to
> say that the bug was the assert, and not the surrounding code?  For
> example, consider this code:
> > >
> > > assert(p);
> > > int x = *p;
> >
> > Should be written as:
> >
> > assert(p);
> > if (!p)
> >     do_something_correct();
> > else
> >     int x = *p;
> >
> > >
> > > Should this assert also not be here in library code?  I mean it's
> obvious that the program is about to crash if p is invalid.  Asserts should
> mean "you're about to invoke undefined behavior", and a crash is *better*
> than undefined behavior.  It surfaces the problem so that you can't let it
> slip under the radar, and it also alerts you to the point that the UB is
> invoked, rather than later.
> > >
> > > What about this assert?
> > >
> > > assert(ptr);
> > > int x = strlen(ptr);
> > >
> > > Surely that assert is ok right?  Do we need to check whether ptr is
> valid EVERY SINGLE TIME we invoke strlen, or any other function for that
> matter?  The code would be a disastrous mess.
> >
> > Again, check before you call if this is in a shared library! What is so
> hard about that? It is called software that doesn't crash.
> >
> > assert(ptr)
> > int x = ptr ? strlen(ptr) : 0;
> >
> > I find it hard to believe that you are arguing that you cannot EVER know
> ANYTHING about the state of your program.  :-/
> >
> > This is like arguing that you should run a full heap integrity check
> every time you perform a memory write, just to be sure you aren't about to
> crash.
> >
> > If you make a std::vector<>, do we need to verify that its internal
> pointer is not null before we write to it?   Probably not, right?  Why
> not?  Because it has a specification of how it works, and it is documented
> that you can construct one, you can use it.
> >
> > It's ok to document how functions work, and it is ok to assume that
> functions work the way they claim to work.
>
>
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