Huge improvement in error messages in recent dmd

[mipri]

Consider the following code with an error:

   #! /usr/bin/env rdmd
   import std;
   void main() {
       auto pts = Array!(int[])([0, 0], [5, 5], [0, 1], [0, 2]);
       multiSort!("a[0] < b[0]", "a[1] < b[1]", 
SwapStrategy.unstable)(pts);
   }

The latest version of dmd that's packaged with Fedora is
2.086.1. Of this code it says:

./x266.d(5): Error: template 
std.algorithm.sorting.multiSort!("a[0] < b[0]", "a[1] < b[1]", 
cast(SwapStrategy)0).multiSort cannot deduce function from 
argument types !()(Array!(int[])), candidates are:
/usr/include/dmd/phobos/std/algorithm/sorting.d(1463):        
std.algorithm.sorting.multiSort!("a[0] < b[0]", "a[1] < b[1]", 
cast(SwapStrategy)0).multiSort(Range)(Range r) if 
(validPredicates!(ElementType!Range, less) && 
hasSwappableElements!Range)

The nightly I have is v2.089.1-beta.1, and it says:

x266.d(5): Error: template std.algorithm.sorting.multiSort!("a[0] 
< b[0]", "a[1] < b[1]", cast(SwapStrategy)0).multiSort cannot 
deduce function from argument types !()(Array!(int[])), 
candidates are:
/edit/nightly/dmd2/linux/bin64/../../src/phobos/std/algorithm/sorting.d(1466):        multiSort(Range)(Range r)
   with Range = Array!(int[])
   must satisfy the following constraint:
        hasSwappableElements!Range

Which is a huge, huge improvement! The problem is that
Array!(Point) doesn't satisfy hasSwappableElements.

I saw that this was also in the v2.089.0 compiler, and so
checked the blog for announcements back to v2.087, and none of
them showed how much better the error messages got. This should
be highlighted. I don't normally care that much about staying
exactly up-to-date with compilers, but I'd sure have upgraded
earlier for this.

A slightly strange thing is that rdmd's error messages are
even friendlier (v2.089.0):

   ./x266.d(5): Error: template 
std.algorithm.sorting.multiSort!("a[0] < b[0]", "a[1] < b[1]", 
cast(SwapStrategy)0).multiSort cannot deduce function from 
argument types !()(Array!(int[])), candidates are:
   
/edit/latest/dmd2/linux/bin64/../../src/phobos/std/algorithm/sorting.d(1466):        multiSort(Range)(Range r)
     with Range = Array!(int[])
     whose parameters have the following constraints:
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       validPredicates!(ElementType!Range, less)
     > hasSwappableElements!Range
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     Tip: not satisfied constraints are marked with >

wow!