feat(grfn/achilles): Implement tuples, and tuple patterns r/2522

Implement tuple expressions, types, and patterns, all the way through
the parser down to the typechecker. In LLVM, these are implemented as
anonymous structs, using an `extract` instruction when they're pattern
matched on to get out the individual fields.

Currently the only limitation here is patterns aren't supported in
function argument position, but you can still do something like

    fn xy = let (x, y) = xy in x + y

Change-Id: I357f17e9d4052e741eda8605b6662822f331efde
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3027
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

2 files changed, 23 insertions, 7 deletions

diff --git a/users/grfn/achilles/src/passes/hir/mod.rs b/users/grfn/achilles/src/passes/hir/mod.rs
index 845bfcb7ab6a..872c449eb020 100644
--- a/users/grfn/achilles/src/passes/hir/mod.rs
+++ b/users/grfn/achilles/src/passes/hir/mod.rs
@@ -1,6 +1,6 @@
 use std::collections::HashMap;
 
-use crate::ast::hir::{Binding, Decl, Expr};
+use crate::ast::hir::{Binding, Decl, Expr, Pattern};
 use crate::ast::{BinaryOperator, Ident, Literal, UnaryOperator};
 
 pub(crate) mod monomorphize;
@@ -29,9 +29,12 @@ pub(crate) trait Visitor<'a, 'ast, T: 'ast>: Sized + 'a {
         Ok(())
     }
 
+    fn visit_pattern(&mut self, _pat: &mut Pattern<'ast, T>) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
     fn visit_binding(&mut self, binding: &mut Binding<'ast, T>) -> Result<(), Self::Error> {
-        self.visit_ident(&mut binding.ident)?;
-        self.visit_type(&mut binding.type_)?;
+        self.visit_pattern(&mut binding.pat)?;
         self.visit_expr(&mut binding.body)?;
         Ok(())
     }
@@ -54,6 +57,13 @@ pub(crate) trait Visitor<'a, 'ast, T: 'ast>: Sized + 'a {
         Ok(())
     }
 
+    fn visit_tuple(&mut self, members: &mut Vec<Expr<'ast, T>>) -> Result<(), Self::Error> {
+        for expr in members {
+            self.visit_expr(expr)?;
+        }
+        Ok(())
+    }
+
     fn pre_visit_expr(&mut self, _expr: &mut Expr<'ast, T>) -> Result<(), Self::Error> {
         Ok(())
     }
@@ -137,12 +147,16 @@ pub(crate) trait Visitor<'a, 'ast, T: 'ast>: Sized + 'a {
                 self.visit_type(type_)?;
                 self.post_visit_call(fun, type_args, args)?;
             }
+            Expr::Tuple(tup, type_) => {
+                self.visit_tuple(tup)?;
+                self.visit_type(type_)?;
+            }
         }
 
         Ok(())
     }
 
-    fn post_visit_decl(&mut self, decl: &'a Decl<'ast, T>) -> Result<(), Self::Error> {
+    fn post_visit_decl(&mut self, _decl: &'a Decl<'ast, T>) -> Result<(), Self::Error> {
         Ok(())
     }
 
diff --git a/users/grfn/achilles/src/passes/hir/strip_positive_units.rs b/users/grfn/achilles/src/passes/hir/strip_positive_units.rs
index 91b56551c82d..85ee1cce4859 100644
--- a/users/grfn/achilles/src/passes/hir/strip_positive_units.rs
+++ b/users/grfn/achilles/src/passes/hir/strip_positive_units.rs
@@ -1,7 +1,7 @@
 use std::collections::HashMap;
 use std::mem;
 
-use ast::hir::Binding;
+use ast::hir::{Binding, Pattern};
 use ast::Literal;
 use void::{ResultVoidExt, Void};
 
@@ -42,8 +42,10 @@ impl<'a, 'ast> Visitor<'a, 'ast, ast::Type<'ast>> for StripPositiveUnits {
                 bindings: extracted
                     .into_iter()
                     .map(|expr| Binding {
-                        ident: Ident::from_str_unchecked("___discarded"),
-                        type_: expr.type_().clone(),
+                        pat: Pattern::Id(
+                            Ident::from_str_unchecked("___discarded"),
+                            expr.type_().clone(),
+                        ),
                         body: expr,
                     })
                     .collect(),