For completions of union type, get all possible properties

Author: Andy Hanson

src/compiler/checker.ts

@@ -204,7 +204,8 @@ namespace ts {
                 // since we are only interested in declarations of the module itself
                 return tryFindAmbientModule(moduleName, /*withAugmentations*/ false);
             },
-            getApparentType
+            getApparentType,
+            getAllPossiblePropertiesOfType,
         };
 
         const tupleTypes: GenericType[] = [];
@@ -5648,6 +5649,22 @@ namespace ts {
                 getPropertiesOfObjectType(type);
         }
 
+        function getAllPossiblePropertiesOfType(type: Type): Symbol[] {
+            if (type.flags & TypeFlags.Union) {
+                const props = createMap<Symbol>();
+                for (const memberType of (type as UnionType).types) {
+                    for (const { name } of getPropertiesOfType(memberType)) {
+                        if (!props.has(name)) {
+                            props.set(name, createUnionOrIntersectionProperty(type as UnionType, name));
+                        }
+                    }
+                }
+                return arrayFrom(props.values());
+            } else {
+                return getPropertiesOfType(type);
+            }
+        }
+
         function getConstraintOfType(type: TypeVariable | UnionOrIntersectionType): Type {
             return type.flags & TypeFlags.TypeParameter ? getConstraintOfTypeParameter(<TypeParameter>type) :
                 type.flags & TypeFlags.IndexedAccess ? getConstraintOfIndexedAccess(<IndexedAccessType>type) :

src/compiler/types.ts

@@ -2564,6 +2564,11 @@ namespace ts {
         /* @internal */ getIdentifierCount(): number;
         /* @internal */ getSymbolCount(): number;
         /* @internal */ getTypeCount(): number;
+
+        /** For a union, will include a property if it's defined in *any* of the member types.
+         * So for `{ a } | { b }`, this will include both `a` and `b`.
+         */
+        /* @internal */ getAllPossiblePropertiesOfType(type: Type): Symbol[];
     }
 
     export enum NodeBuilderFlags {

src/services/completions.ts

@@ -813,19 +813,16 @@ namespace ts.Completions {
             // We're looking up possible property names from contextual/inferred/declared type.
             isMemberCompletion = true;
 
-            let typeForObject: Type;
+            let typeMembers: Symbol[];
             let existingMembers: Declaration[];
 
             if (objectLikeContainer.kind === SyntaxKind.ObjectLiteralExpression) {
                 // We are completing on contextual types, but may also include properties
                 // other than those within the declared type.
                 isNewIdentifierLocation = true;
-
-                // If the object literal is being assigned to something of type 'null | { hello: string }',
-                // it clearly isn't trying to satisfy the 'null' type. So we grab the non-nullable type if possible.
-                typeForObject = typeChecker.getContextualType(<ObjectLiteralExpression>objectLikeContainer);
-                typeForObject = typeForObject && typeForObject.getNonNullableType();
-
+                const typeForObject = typeChecker.getContextualType(<ObjectLiteralExpression>objectLikeContainer);
+                if (!typeForObject) return false;
+                typeMembers = typeChecker.getAllPossiblePropertiesOfType(typeForObject);
                 existingMembers = (<ObjectLiteralExpression>objectLikeContainer).properties;
             }
             else if (objectLikeContainer.kind === SyntaxKind.ObjectBindingPattern) {
@@ -849,7 +846,10 @@ namespace ts.Completions {
                         }
                     }
                     if (canGetType) {
-                        typeForObject = typeChecker.getTypeAtLocation(objectLikeContainer);
+                        const typeForObject = typeChecker.getTypeAtLocation(objectLikeContainer);
+                        if (!typeForObject) return false;
+                        // In a binding pattern, get only known properties. Everywhere else we will get all possible properties.
+                        typeMembers = typeChecker.getPropertiesOfType(typeForObject);
                         existingMembers = (<ObjectBindingPattern>objectLikeContainer).elements;
                     }
                 }
@@ -861,11 +861,6 @@ namespace ts.Completions {
                 Debug.fail("Expected object literal or binding pattern, got " + objectLikeContainer.kind);
             }
 
-            if (!typeForObject) {
-                return false;
-            }
-
-            const typeMembers = typeChecker.getPropertiesOfType(typeForObject);
             if (typeMembers && typeMembers.length > 0) {
                 // Add filtered items to the completion list
                 symbols = filterObjectMembersList(typeMembers, existingMembers);

tests/cases/fourslash/completionListOfUnion.ts

@@ -0,0 +1,18 @@
+/// <reference path='fourslash.ts' />
+
+// @strictNullChecks: true
+
+// Non-objects should be skipped, so `| number | null` should have no effect on completions.
+////const x: { a: number, b: number } | { a: string, c: string } | { b: boolean } | number | null = { /*x*/ };
+
+////interface I { a: number; }
+////function f(...args: Array<I | I[]>) {}
+////f({ /*f*/ });
+
+goTo.marker("x");
+verify.completionListContains("a", "(property) a: string | number");
+verify.completionListContains("b", "(property) b: number | boolean");
+verify.completionListContains("c", "(property) c: string");
+
+goTo.marker("f");
+verify.completionListContains("a", "(property) a: number");