> Virgil is fully self-hosted: its entire compiler and runtime system is impleme...

titzer · on July 2, 2022

You cannot bootstrap any language entirely from source, you always need a compiler or interpreter written in another language.

Virgil bootstrapped for the first time using an interpreter I wrote in Java, back around 2009. When the new compiler could finally compile itself well enough to be stable, I checked in the first bootstrap binary, a jar file. Since then, every once in a while (41 times so far), when a major set of bugfixes or new features is done, I've rev'd stable by checking in binaries that are generated by the first compiling the existing code with the stable compiler, and then compiling the compiler with that compiler. I generally wait several stable revisions before using new features in the compiler. What that means is that you can always compile the source in the repo with the stable binary in the repo, and that compiler can compile itself again too, and both should behave identically. You can usually even go back a revision, but I've never had to do that.

There is a full interpreter built into the compiler as well, so if there is a bug in the stable compiler's codegen that is a showstopper, it can be fixed in the source and then the new source run in the interpreter of the old compiler in order to get a new stable binary. I've never had that happen, though.

pabs3 · on July 2, 2022

I'd encourage you to write a smaller implementation for bootstrap of Virgil in a couple of other languages, so that folks who don't trust binaries can still use your language.

The Bootstrappable Builds folks are working on this for every part of a modern Linux distro. The main approaches are alternative smaller implementations written in other languages (including interpreters) and also compiling with chains of older versions that were written in other languages. They are also working on a full bootstrap from ~512 bytes of machine code plus a ton of source all the way up to a full Linux distro. They have gotten quite far in that and are continually improving the situation everywhere.