From f285e7ce930b3b79b63ee172c79d9c8b1d427425 Mon Sep 17 00:00:00 2001
From: Folkert <folkert@folkertdev.nl>
Date: Wed, 18 May 2022 16:39:24 +0200
Subject: [PATCH] add a TypedHole node to Expr, for use in the editor

---
 compiler/can/src/expr.rs       | 12 +++++++++---
 compiler/can/src/module.rs     |  1 +
 compiler/can/src/traverse.rs   |  1 +
 compiler/constrain/src/expr.rs |  9 +++++++++
 compiler/mono/src/copy.rs      |  2 ++
 compiler/mono/src/ir.rs        |  1 +
 6 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/compiler/can/src/expr.rs b/compiler/can/src/expr.rs
index ec1c8080bb..e2db985092 100644
--- a/compiler/can/src/expr.rs
+++ b/compiler/can/src/expr.rs
@@ -204,10 +204,13 @@ pub enum Expr {
         lambda_set_variables: Vec<LambdaSet>,
     },
 
-    // Test
+    /// Test
     Expect(Box<Loc<Expr>>, Box<Loc<Expr>>),
 
-    // Compiles, but will crash if reached
+    /// Rendered as empty box in editor
+    TypedHole(Variable),
+
+    /// Compiles, but will crash if reached
     RuntimeError(RuntimeError),
 }
 
@@ -247,7 +250,9 @@ impl Expr {
             },
             &Self::OpaqueRef { name, .. } => Category::OpaqueWrap(name),
             Self::Expect(..) => Category::Expect,
-            Self::RuntimeError(..) => Category::Unknown,
+
+            // these nodes place no constraints on the expression's type
+            Self::TypedHole(_) | Self::RuntimeError(..) => Category::Unknown,
         }
     }
 }
@@ -1391,6 +1396,7 @@ pub fn inline_calls(var_store: &mut VarStore, scope: &mut Scope, expr: Expr) ->
         | other @ Var(_)
         | other @ AbilityMember(..)
         | other @ RunLowLevel { .. }
+        | other @ TypedHole { .. }
         | other @ ForeignCall { .. } => other,
 
         List {
diff --git a/compiler/can/src/module.rs b/compiler/can/src/module.rs
index 4abd93c703..e93e17b7c7 100644
--- a/compiler/can/src/module.rs
+++ b/compiler/can/src/module.rs
@@ -710,6 +710,7 @@ fn fix_values_captured_in_closure_expr(
         | Var(_)
         | AbilityMember(..)
         | EmptyRecord
+        | TypedHole { .. }
         | RuntimeError(_)
         | ZeroArgumentTag { .. }
         | Accessor { .. } => {}
diff --git a/compiler/can/src/traverse.rs b/compiler/can/src/traverse.rs
index 5938c2fc3a..71f61f7f82 100644
--- a/compiler/can/src/traverse.rs
+++ b/compiler/can/src/traverse.rs
@@ -168,6 +168,7 @@ pub fn walk_expr<V: Visitor>(visitor: &mut V, expr: &Expr, var: Variable) {
             visitor.visit_expr(&e1.value, e1.region, Variable::NULL);
             visitor.visit_expr(&e2.value, e2.region, Variable::NULL);
         }
+        Expr::TypedHole(_) => { /* terminal */ }
         Expr::RuntimeError(..) => { /* terminal */ }
     }
 }
diff --git a/compiler/constrain/src/expr.rs b/compiler/constrain/src/expr.rs
index 83abcc8f71..5a106697cc 100644
--- a/compiler/constrain/src/expr.rs
+++ b/compiler/constrain/src/expr.rs
@@ -1144,6 +1144,15 @@ pub fn constrain_expr(
             arg_cons.push(eq);
             constraints.exists_many(vars, arg_cons)
         }
+        TypedHole(var) => {
+            // store the expected type for this position
+            constraints.equal_types_var(
+                *var,
+                expected,
+                Category::Storage(std::file!(), std::line!()),
+                region,
+            )
+        }
         RuntimeError(_) => {
             // Runtime Errors have no constraints because they're going to crash.
             Constraint::True
diff --git a/compiler/mono/src/copy.rs b/compiler/mono/src/copy.rs
index 35c94df620..b4dc4348d7 100644
--- a/compiler/mono/src/copy.rs
+++ b/compiler/mono/src/copy.rs
@@ -366,6 +366,8 @@ pub fn deep_copy_type_vars_into_expr<'a>(
 
             Expect(e1, e2) => Expect(Box::new(e1.map(go_help)), Box::new(e2.map(go_help))),
 
+            TypedHole(v) => TypedHole(sub!(*v)),
+
             RuntimeError(err) => RuntimeError(err.clone()),
         }
     }
diff --git a/compiler/mono/src/ir.rs b/compiler/mono/src/ir.rs
index e57a76a69a..cb5aa3115e 100644
--- a/compiler/mono/src/ir.rs
+++ b/compiler/mono/src/ir.rs
@@ -5235,6 +5235,7 @@ pub fn with_hole<'a>(
                 }
             }
         }
+        TypedHole(_) => Stmt::RuntimeError("Hit a blank"),
         RuntimeError(e) => Stmt::RuntimeError(env.arena.alloc(format!("{:?}", e))),
     }
 }