Mark promises covariant on JS

aantron · Dec 30, 2019 · c9d8008 · c9d8008
1 parent 69dc502
commit c9d8008
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Showing 3 changed files with 65 additions and 8 deletions.
diff --git a/src/js/promise.re b/src/js/promise.re
@@ -4,11 +4,11 @@
 
 
 
-type rejectable('a, 'e);
+type rejectable(+'a, +'e);
 type never;
 
-type promise('a) = rejectable('a, never);
-type t('a) = promise('a);
+type promise(+'a) = rejectable('a, never);
+type t(+'a) = promise('a);
 
 
 

diff --git a/src/js/promise.rei b/src/js/promise.rei
@@ -4,11 +4,11 @@
 
 
 
-type rejectable('a, 'e);                    /* Internal; use Promise.Js.t. */
+type rejectable(+'a, +'e);                  /* Internal; use Promise.Js.t. */
 type never;
 
-type promise('a) = rejectable('a, never);   /* Internal; use Promise.t. */
-type t('a) = promise('a);
+type promise(+'a) = rejectable('a, never);  /* Internal; use Promise.t. */
+type t(+'a) = promise('a);
 
 
 
@@ -155,7 +155,7 @@ let all6:
 
 /* For writing bindings. */
 module Js: {
-  type t('a, 'e) = rejectable('a, 'e);
+  type t(+'a, +'e) = rejectable('a, 'e);
 
   /* Making. */
   let pending:

diff --git a/test/js/test_ffi.re b/test/js/test_ffi.re
@@ -304,4 +304,61 @@ let curryTests = Framework.suite("curry", [
 
 
 
-let suites = [interopTests, soundnessTests, curryTests];
+type type_ = [
+  | `A
+  | `B
+]
+
+type subtype = [
+  | `A
+]
+
+let covarianceTests = Framework.suite("covariance", [
+  test("promise", () => {
+    let p: Promise.t(subtype) = Promise.resolved(`A);
+    let p: Promise.t(type_) = (p :> Promise.t(type_));
+    ignore(p);
+    Promise.resolved(true);
+  }),
+
+  test("ok", () => {
+    let p: Promise.t(result(subtype, unit)) = Promise.resolved(Ok(`A));
+    let p: Promise.t(result(type_, unit)) =
+      (p :> Promise.t(result(type_, unit)));
+    ignore(p);
+    Promise.resolved(true);
+  }),
+
+  test("error", () => {
+    let p: Promise.t(result(unit, subtype)) = Promise.resolved(Error(`A));
+    let p: Promise.t(result(unit, type_)) =
+      (p :> Promise.t(result(unit, type_)));
+    ignore(p);
+    Promise.resolved(true);
+  }),
+
+  test("option", () => {
+    let p: Promise.t(option(subtype)) = Promise.resolved(Some(`A));
+    let p: Promise.t(option(type_)) = (p :> Promise.t(option(type_)));
+    ignore(p);
+    Promise.resolved(true);
+  }),
+
+  test("fulfillment", () => {
+    let p: Promise.Js.t(subtype, unit) = Promise.Js.resolved(`A);
+    let p: Promise.Js.t(type_, unit) = (p :> Promise.Js.t(type_, unit));
+    ignore(p);
+    Promise.resolved(true);
+  }),
+
+  test("rejection", () => {
+    let p: Promise.Js.t(unit, subtype) = Promise.Js.rejected(`A);
+    let p: Promise.Js.t(unit, type_) = (p :> Promise.Js.t(unit, type_));
+    p->Promise.Js.catch(_ => Promise.resolved())->ignore;
+    Promise.resolved(true);
+  }),
+]);
+
+
+
+let suites = [interopTests, soundnessTests, curryTests, covarianceTests];