My late christmas present for you: context-aware assertion error messages

[Seb]

On Monday, 14 January 2019 at 14:15:45 UTC, Atila Neves wrote:
> On Saturday, 12 January 2019 at 15:34:02 UTC, Seb wrote:
>> tl;dr: I was annoyed for years that D's assert are so non 
>> informative AssertError, so here's my late Christmas present 
>> for the D community. With 2.085 DMD will gain an experimental 
>> flag for more informative assertion errors. Feedback on this 
>> experimental feature is welcome, s.t. we eventually can enable 
>> it by default.
>>
>> [...]
>
> Awesome.
>
> It's obvious that assertions for equality are the most common, 
> I wonder how easy it would be to get other changes merged like 
> `assert(foo in bar)`.

Should be easy enough:

https://github.com/dlang/dmd/pull/9264
https://github.com/dlang/druntime/pull/2463

Also note that other trivial stuff like `a < b` is already 
supported.
See e.g.: 
https://github.com/dlang/druntime/blob/master/test/exceptions/src/assert_fail.d

> There are also all the assertions that make use of `equal` 
> because of ranges.

In theory we could hard-code a check for the symbol in DMD and 
see whether its std.algorithm.comparison.equal, but ranges are 
tricky as both might have been consumed by `equal` and you would 
then end up printing e.g. sth. like:

[] != []

> I'd really like is access to the AST in the assert but alas I 
> don't think that will ever be possible.

Yeah :/