Migrating D front end to D - post Dconf

[Walter Bright]

On 5/11/2013 7:30 PM, Jonathan M Davis wrote:
> But in theory, the way to solve the problem of your program not compiling with
> the new compiler is to compile with the compiler it was developed with in the
> first place, and then if you want to upgrade your code, you upgrade your code
> and use it with the new compiler. The big problem is when you need to compile
> the compiler. You have a circular dependency due to the compiler depending on
> itself, and have to break it somehow. As long as newer compilers can compiler
> older ones, you're fine, but that's bound to fall apart at some point unless
> you freeze everything. But even bug fixes could make the old compiler not
> compile anymore, so unless the language and compiler (and anything they depend
> on) is extremely stable, you risk not being able to compile older compilers,
> and it's hard to guarantee that level of stability, especially if the compiler
> is not restricted in what features it uses or in what it uses from the
> standard library.

It isn't just compiling the older compiler, it is compiling it and verifying 
that it works.

At least for dmd, we keep all the old binaries up and downloadable for that reason.