From 203f7a8f55ee63b4a8026f5b9b067081cb3de810 Mon Sep 17 00:00:00 2001
From: Markus Westerlind <marwes91@gmail.com>
Date: Thu, 25 Oct 2018 08:25:56 +0200
Subject: [PATCH] Row polymorphic variants

---
 check/src/typecheck.rs |  8 ++++++++
 check/tests/pass.rs    | 20 ++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/check/src/typecheck.rs b/check/src/typecheck.rs
index ae8f40aedf..03c62c7744 100644
--- a/check/src/typecheck.rs
+++ b/check/src/typecheck.rs
@@ -1984,6 +1984,13 @@ impl<'a> Typecheck<'a> {
                 self.translate_ast_type(&type_cache, typ)
             });
 
+            if let Type::Variant(ref row) = **alias.unresolved_type().remove_forall() {
+                for field in row.row_iter() {
+                    let symbol = self.symbols.scoped_symbol(field.name.as_ref());
+                    self.original_symbols.insert(field.name.clone(), symbol);
+                }
+            }
+
             // alias.unresolved_type() is a dummy in this context
             self.named_variables.extend(
                 alias
@@ -1994,6 +2001,7 @@ impl<'a> Typecheck<'a> {
 
             let replacement = self.create_unifiable_signature2(alias.unresolved_type());
 
+
             if let Some(typ) = replacement {
                 *alias.unresolved_type_mut() = typ;
             }
diff --git a/check/tests/pass.rs b/check/tests/pass.rs
index fa8a35b85d..1eac439622 100644
--- a/check/tests/pass.rs
+++ b/check/tests/pass.rs
@@ -970,3 +970,23 @@ fn consider_the_type_of_the_splat_record() {
 
     assert_req!(result.map(|t| t.to_string()), Ok("{ x : Int, y : Int }"));
 }
+
+#[test]
+fn polymorphic_variants() {
+    let _ = env_logger::try_init();
+
+    let text = r#"
+type AA r = (| A Int .. r)
+type BB r = (| B String .. r)
+if True then
+    A 123
+else
+    B "abc"
+"#;
+    let result = support::typecheck(text);
+
+    assert_req!(
+        result.map(|t| t.to_string()),
+        Ok("forall a . | test.A Int | test.B String | a")
+    );
+}