What do you want to see for a mature DLang?

[vit]

On Friday, 29 December 2017 at 07:53:51 UTC, IM wrote:
> I will start:
>
>    -- Better compiler errors, better compiler errors, better 
> compiler errors.
>
>
> I really wish that the compiler errors could receive some 
> refinement. Mostly it feels like some error text just being 
> thrown at me. It needs to be better formatted, more helpful, 
> with suggestions about how to fix (if possible).
>
> To illustrate my point:
>
> - See the compile errors I've just encountered with DMD: 
> https://cdn.pbrd.co/images/H0q609l.png
>
> - Now compare that with an error produced by rustc:
> https://cdn.pbrd.co/images/H0q6bLi.png
>
>
> Simple things like these make a big difference. D Lang has been 
> around for a long while now, and hence signs of its maturity 
> has to show everywhere, especially in the compiler, as well as 
> the package manager.


Similar problem is when some template with alias callback fail to 
instantiate because callback contains error.
Example:

void foo(){
     string str = 1;

     /++ nice error message:
         Error: cannot implicitly convert expression `1` of type 
`int` to `string`

     +/


     import std.algorithm;

     [1, 2, 3].each!((x){
         string str = 1        ///same error
     });

     /++ horrible error message without root cause:
     source\app.d(660,14): Error: template app.foo.each!((x)

	{

	string str = 1;

	}

	).each cannot deduce function from argument types !()(int[]), 
candidates are:
	C:\D\dmd2\windows\bin\..\..\src\phobos\std\algorithm\iteration.d(899,10):        app.foo.each!((x)

	{

	string str = 1;

	}

	).each(Range)(Range r) if (!isForeachIterable!Range && 
(isRangeIterable!Range || __traits(compiles, 
typeof(r.front).length)))
	C:\D\dmd2\windows\bin\..\..\src\phobos\std\algorithm\iteration.d(934,10):        app.foo.each!((x)

	{

	string str = 1;

	}

	).each(Iterable)(auto ref Iterable r) if 
(isForeachIterable!Iterable || __traits(compiles, 
Parameters!(Parameters!(r.opApply))))

     +/
}