From 8594b6e2a94d470fc93e76ca3ac4619d0167f046 Mon Sep 17 00:00:00 2001
From: James Shubin <james@shubin.ca>
Date: Wed, 21 Aug 2024 19:00:51 -0400
Subject: [PATCH] lang: funcs: Hint the struct_lookup functions better

If we have static information, use it to help unification.
---
 lang/funcs/struct_lookup_func.go                  | 10 ++++++++++
 lang/funcs/struct_lookup_optional_func.go         | 10 ++++++++++
 .../TestAstFunc2/structlookup3.txtar              | 15 +++++++++++++++
 3 files changed, 35 insertions(+)
 create mode 100644 lang/interpret_test/TestAstFunc2/structlookup3.txtar

diff --git a/lang/funcs/struct_lookup_func.go b/lang/funcs/struct_lookup_func.go
index d63bac75..359b18bc 100644
--- a/lang/funcs/struct_lookup_func.go
+++ b/lang/funcs/struct_lookup_func.go
@@ -125,6 +125,16 @@ func (obj *StructLookupFunc) FuncInfer(partialType *types.Type, partialValues []
 	// This can happen at runtime too, but we save it here for Build()!
 	obj.field = s // store for later
 
+	// Figure out more about the sig if any information is known statically.
+	if len(partialType.Ord) > 0 && partialType.Map[partialType.Ord[0]] != nil {
+		obj.Type = partialType.Map[partialType.Ord[0]] // assume this
+		if obj.Type.Kind == types.KindStruct && obj.Type.Map != nil {
+			if typ, exists := obj.Type.Map[s]; exists {
+				obj.Out = typ
+			}
+		}
+	}
+
 	// This isn't precise enough because we must guarantee that the field is
 	// in the struct and that ?1 is actually a struct, but that's okay it is
 	// something that we'll verify at build time!
diff --git a/lang/funcs/struct_lookup_optional_func.go b/lang/funcs/struct_lookup_optional_func.go
index 4c8c6f5b..a1176dc4 100644
--- a/lang/funcs/struct_lookup_optional_func.go
+++ b/lang/funcs/struct_lookup_optional_func.go
@@ -132,6 +132,16 @@ func (obj *StructLookupOptionalFunc) FuncInfer(partialType *types.Type, partialV
 	// This can happen at runtime too, but we save it here for Build()!
 	//obj.field = s // don't store for this optional lookup version!
 
+	// Figure out more about the sig if any information is known statically.
+	if len(partialType.Ord) > 0 && partialType.Map[partialType.Ord[0]] != nil {
+		obj.Type = partialType.Map[partialType.Ord[0]] // assume this
+		if obj.Type.Kind == types.KindStruct && obj.Type.Map != nil {
+			if typ, exists := obj.Type.Map[s]; exists {
+				obj.Out = typ
+			}
+		}
+	}
+
 	// This isn't precise enough because we must guarantee that the field is
 	// in the struct and that ?1 is actually a struct, but that's okay it is
 	// something that we'll verify at build time! (Or skip it for optional!)
diff --git a/lang/interpret_test/TestAstFunc2/structlookup3.txtar b/lang/interpret_test/TestAstFunc2/structlookup3.txtar
new file mode 100644
index 00000000..f6917fe4
--- /dev/null
+++ b/lang/interpret_test/TestAstFunc2/structlookup3.txtar
@@ -0,0 +1,15 @@
+-- main.mcl --
+import "fmt"
+
+$st = struct{
+	field1 => "value1",
+	field2 => "value2",
+}
+
+class test_struct_lookup($v1, $v2) {
+	test "test-${v1}-${v2}" {}
+}
+
+include test_struct_lookup($st->field1, $st->field2)
+-- OUTPUT --
+Vertex: test[test-value1-value2]