feat(achilles): Implement a Unit type r/2356

Add support for a zero-sized Unit type. This requires some special at
the codegen level because LLVM (unsurprisingly) only allows Void types
in function return position - to make that a little easier to handle
there's a new pass that strips any unit-only expressions and pulls
unit-only function arguments up to new `let` bindings, so we never have
to actually pass around unit values.

Change-Id: I0fc18a516821f2d69172c42a6a5d246b23471e38
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2695
Reviewed-by: glittershark <grfn@gws.fyi>
Tested-by: BuildkiteCI

1 files changed, 3 insertions, 2 deletions

diff --git a/users/glittershark/achilles/src/compiler.rs b/users/glittershark/achilles/src/compiler.rs
index 7001e5a9a3..45b215473d 100644
--- a/users/glittershark/achilles/src/compiler.rs
+++ b/users/glittershark/achilles/src/compiler.rs
@@ -8,7 +8,7 @@ use test_strategy::Arbitrary;
 
 use crate::codegen::{self, Codegen};
 use crate::common::Result;
-use crate::passes::hir::monomorphize;
+use crate::passes::hir::{monomorphize, strip_positive_units};
 use crate::{parser, tc};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Arbitrary)]
@@ -55,9 +55,10 @@ pub struct CompilerOptions {
 
 pub fn compile_file(input: &Path, output: &Path, options: &CompilerOptions) -> Result<()> {
     let src = fs::read_to_string(input)?;
-    let (_, decls) = parser::toplevel(&src)?; // TODO: statements
+    let (_, decls) = parser::toplevel(&src)?;
     let mut decls = tc::typecheck_toplevel(decls)?;
     monomorphize::run_toplevel(&mut decls);
+    strip_positive_units::run_toplevel(&mut decls);
 
     let context = codegen::Context::create();
     let mut codegen = Codegen::new(