Instantiate variant types as needed

CHANGELOG.md

@@ -32,6 +32,7 @@
 - Fix JS syntax highlighting in single-line FFI extension points. https://github.com/rescript-lang/rescript-vscode/pull/807
 - Fix signature help in uncurried mode. https://github.com/rescript-lang/rescript-vscode/pull/809
 - Fix various issues in uncurried mode. https://github.com/rescript-lang/rescript-vscode/pull/810
+- Fixes a bug in pattern completion where for example `result` wouldn't complete, due to type variables getting lost/not being instantiated. https://github.com/rescript-lang/rescript-vscode/pull/814
 
 ## 1.18.0
 

analysis/src/SharedTypes.ml

@@ -320,6 +320,8 @@ and completionType =
       constructors: Constructor.t list;
       variantDecl: Types.type_declaration;
       variantName: string;
+      typeArgs: Types.type_expr list;
+      typeParams: Types.type_expr list;
     }
   | Tpolyvariant of {
       env: QueryEnv.t;

analysis/src/TypeUtils.ml

@@ -128,14 +128,23 @@ let rec extractType ~env ~package (t : Types.type_expr) =
     | args, _tRet when args <> [] ->
       Some (Tfunction {env; args; typ = t; uncurried = true})
     | _args, _tRet -> None)
-  | Tconstr (path, _, _) -> (
+  | Tconstr (path, typeArgs, _) -> (
     match References.digConstructor ~env ~package path with
-    | Some (env, {item = {decl = {type_manifest = Some t1}}}) ->
-      extractType ~env ~package t1
-    | Some (env, {name; item = {decl; kind = Type.Variant constructors}}) ->
+    | Some (_env, {item = {decl = {type_manifest = Some t1; type_params}}}) ->
+      t1
+      |> instantiateType ~typeParams:type_params ~typeArgs
+      |> extractType ~env ~package
+    | Some (_env, {name; item = {decl; kind = Type.Variant constructors}}) ->
       Some
         (Tvariant
-           {env; constructors; variantName = name.txt; variantDecl = decl})
+           {
+             env;
+             constructors;
+             variantName = name.txt;
+             variantDecl = decl;
+             typeArgs;
+             typeParams = decl.type_params;
+           })
     | Some (env, {item = {kind = Record fields}}) ->
       Some (Trecord {env; fields; definition = `TypeExpr t})
     | _ -> None)
@@ -280,7 +289,14 @@ let extractTypeFromResolvedType (typ : Type.t) ~env ~full =
   | Variant constructors ->
     Some
       (Tvariant
-         {env; constructors; variantName = typ.name; variantDecl = typ.decl})
+         {
+           env;
+           constructors;
+           variantName = typ.name;
+           variantDecl = typ.decl;
+           typeParams = typ.decl.type_params;
+           typeArgs = [];
+         })
   | Abstract _ | Open -> (
     match typ.decl.type_manifest with
     | None -> None
@@ -345,8 +361,8 @@ let rec resolveNested ~env ~full ~nested ?ctx (typ : completionType) =
       typ
       |> extractType ~env ~package:full.package
       |> Utils.Option.flatMap (fun t -> t |> resolveNested ~env ~full ~nested)
-    | NVariantPayload {constructorName; itemNum}, Tvariant {env; constructors}
-      -> (
+    | ( NVariantPayload {constructorName; itemNum},
+        Tvariant {env; constructors; typeParams; typeArgs} ) -> (
       match
         constructors
         |> List.find_opt (fun (c : Constructor.t) ->
@@ -357,6 +373,7 @@ let rec resolveNested ~env ~full ~nested ?ctx (typ : completionType) =
         | None -> None
         | Some (typ, _) ->
           typ
+          |> instantiateType ~typeParams ~typeArgs
           |> extractType ~env ~package:full.package
           |> Utils.Option.flatMap (fun typ ->
                  typ |> resolveNested ~env ~full ~nested))

analysis/tests/src/CompletionPattern.res

@@ -211,3 +211,8 @@ let getThing = async () => One
 
 // switch await getThing() { | }
 //                            ^com
+
+let res: result<someVariant, somePolyVariant> = Ok(One)
+
+// switch res { | Ok() }
+//                   ^com

analysis/tests/src/expected/CompletionPattern.res.txt

@@ -1105,3 +1105,39 @@ Path getThing
     "insertTextFormat": 2
   }]
 
+Complete src/CompletionPattern.res 216:21
+posCursor:[216:21] posNoWhite:[216:20] Found pattern:[216:18->216:22]
+Ppat_construct Ok:[216:18->216:20]
+posCursor:[216:21] posNoWhite:[216:20] Found pattern:[216:20->216:22]
+Ppat_construct ():[216:20->216:22]
+Completable: Cpattern Value[res]->variantPayload::Ok($0)
+Package opens Pervasives.JsxModules.place holder
+Resolved opens 1 pervasives
+ContextPath Value[res]
+Path res
+[{
+    "label": "One",
+    "kind": 4,
+    "tags": [],
+    "detail": "One\n\ntype someVariant = One | Two(bool) | Three(someRecord, bool)",
+    "documentation": null,
+    "insertText": "One",
+    "insertTextFormat": 2
+  }, {
+    "label": "Two(_)",
+    "kind": 4,
+    "tags": [],
+    "detail": "Two(bool)\n\ntype someVariant = One | Two(bool) | Three(someRecord, bool)",
+    "documentation": null,
+    "insertText": "Two(${1:_})",
+    "insertTextFormat": 2
+  }, {
+    "label": "Three(_, _)",
+    "kind": 4,
+    "tags": [],
+    "detail": "Three(someRecord, bool)\n\ntype someVariant = One | Two(bool) | Three(someRecord, bool)",
+    "documentation": null,
+    "insertText": "Three(${1:_}, ${2:_})",
+    "insertTextFormat": 2
+  }]
+