Empty object type assignable to mapped type with optional properties

ahejlsberg · ahejlsberg · commit 7e7057a89d67 · 2017-01-30T16:53:31.000-08:00
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -7687,7 +7687,7 @@ namespace ts {
             function isKnownProperty(type: Type, name: string): boolean {
                 if (type.flags & TypeFlags.Object) {
                     const resolved = resolveStructuredTypeMembers(<ObjectType>type);
-                    if ((relation === assignableRelation || relation === comparableRelation) && (type === globalObjectType || isEmptyObjectType(resolved)) ||
+                    if ((relation === assignableRelation || relation === comparableRelation) && (type === globalObjectType || isEmptyResolvedType(resolved)) ||
                         resolved.stringIndexInfo ||
                         (resolved.numberIndexInfo && isNumericLiteralName(name)) ||
                         getPropertyOfType(type, name)) {
@@ -7704,14 +7704,18 @@ namespace ts {
                 return false;
             }
 
-            function isEmptyObjectType(t: ResolvedType) {
+            function isEmptyResolvedType(t: ResolvedType) {
                 return t.properties.length === 0 &&
                     t.callSignatures.length === 0 &&
                     t.constructSignatures.length === 0 &&
                     !t.stringIndexInfo &&
                     !t.numberIndexInfo;
             }
 
+            function isEmptyObjectType(type: Type) {
+                return type.flags & TypeFlags.Object && isEmptyResolvedType(resolveStructuredTypeMembers(<ObjectType>type));
+            }
+
             function hasExcessProperties(source: FreshObjectLiteralType, target: Type, reportErrors: boolean): boolean {
                 if (maybeTypeOfKind(target, TypeFlags.Object) && !(getObjectFlags(target) & ObjectFlags.ObjectLiteralPatternWithComputedProperties)) {
                     for (const prop of getPropertiesOfObjectType(source)) {
@@ -7925,10 +7929,14 @@ namespace ts {
                             }
                         }
                     }
+                    else if ((<MappedType>target).declaration.questionToken && isEmptyObjectType(source)) {
+                        return Ternary.True;
+
+                    }
                 }
                 else if (relation !== identityRelation) {
                     const resolved = resolveStructuredTypeMembers(<ObjectType>target);
-                    if (isEmptyObjectType(resolved) || resolved.stringIndexInfo && resolved.stringIndexInfo.type.flags & TypeFlags.Any) {
+                    if (isEmptyResolvedType(resolved) || resolved.stringIndexInfo && resolved.stringIndexInfo.type.flags & TypeFlags.Any) {
                         return Ternary.True;
                     }
                 }

Original file line number	Diff line number	Diff line change
`@@ -7687,7 +7687,7 @@ namespace ts {`
`7687`	`7687`	`function isKnownProperty(type: Type, name: string): boolean {`
`7688`	`7688`	`if (type.flags & TypeFlags.Object) {`
`7689`	`7689`	`const resolved = resolveStructuredTypeMembers(<ObjectType>type);`
`7690`		`- if ((relation === assignableRelation \|\| relation === comparableRelation) && (type === globalObjectType \|\| isEmptyObjectType(resolved)) \|\|`
	`7690`	`+ if ((relation === assignableRelation \|\| relation === comparableRelation) && (type === globalObjectType \|\| isEmptyResolvedType(resolved)) \|\|`
`7691`	`7691`	`resolved.stringIndexInfo \|\|`
`7692`	`7692`	`(resolved.numberIndexInfo && isNumericLiteralName(name)) \|\|`
`7693`	`7693`	`getPropertyOfType(type, name)) {`
`@@ -7704,14 +7704,18 @@ namespace ts {`
`7704`	`7704`	`return false;`
`7705`	`7705`	`}`
`7706`	`7706`
`7707`		`- function isEmptyObjectType(t: ResolvedType) {`
	`7707`	`+ function isEmptyResolvedType(t: ResolvedType) {`
`7708`	`7708`	`return t.properties.length === 0 &&`
`7709`	`7709`	`t.callSignatures.length === 0 &&`
`7710`	`7710`	`t.constructSignatures.length === 0 &&`
`7711`	`7711`	`!t.stringIndexInfo &&`
`7712`	`7712`	`!t.numberIndexInfo;`
`7713`	`7713`	`}`
`7714`	`7714`
	`7715`	`+ function isEmptyObjectType(type: Type) {`
	`7716`	`+ return type.flags & TypeFlags.Object && isEmptyResolvedType(resolveStructuredTypeMembers(<ObjectType>type));`
	`7717`	`+ }`
	`7718`	`+`
`7715`	`7719`	`function hasExcessProperties(source: FreshObjectLiteralType, target: Type, reportErrors: boolean): boolean {`
`7716`	`7720`	`if (maybeTypeOfKind(target, TypeFlags.Object) && !(getObjectFlags(target) & ObjectFlags.ObjectLiteralPatternWithComputedProperties)) {`
`7717`	`7721`	`for (const prop of getPropertiesOfObjectType(source)) {`
`@@ -7925,10 +7929,14 @@ namespace ts {`
`7925`	`7929`	`}`
`7926`	`7930`	`}`
`7927`	`7931`	`}`
	`7932`	`+ else if ((<MappedType>target).declaration.questionToken && isEmptyObjectType(source)) {`
	`7933`	`+ return Ternary.True;`
	`7934`	`+`
	`7935`	`+ }`
`7928`	`7936`	`}`
`7929`	`7937`	`else if (relation !== identityRelation) {`
`7930`	`7938`	`const resolved = resolveStructuredTypeMembers(<ObjectType>target);`
`7931`		`- if (isEmptyObjectType(resolved) \|\| resolved.stringIndexInfo && resolved.stringIndexInfo.type.flags & TypeFlags.Any) {`
	`7939`	`+ if (isEmptyResolvedType(resolved) \|\| resolved.stringIndexInfo && resolved.stringIndexInfo.type.flags & TypeFlags.Any) {`
`7932`	`7940`	`return Ternary.True;`
`7933`	`7941`	`}`
`7934`	`7942`	`}`