Filling in an implementation using VS Code will expand types

Matt Bierner (@mjbvz)

type Foo = [string, number];

interface Bar {
  test(a: Foo): void;
}

class Baz implements Bar{
}

Using fill in Baz implementation quick fix:

type Foo = [string, number];

interface Bar {
  test(a: Foo): void;
}

class Baz implements Bar {
  test(a: [string, number]): void {
    throw new Error("Method not implemented.");
  }
}

I expect:

class Baz implements Bar {
  test(a: Foo): void {
    throw new Error("Method not implemented.");
  }
}

/cc Matt Bierner (@mjbvz)

Looks like we throw away the information for the alias associated with the type of a symbol as part of getTypeOfSymbol, so we will need to modify it or create a helper which tries to retrieve the alias when possible.

I came across this recently. The "Implement interface" quick fix expanded my type aliases, which ended up being super long. It expands type constraints for generic methods, too.

interface MyInterface {
  myProp: string,
  myProp2: string,
}

type FooInterface = MyInterface & { myProp: "foo" };
type Foo2Interface = MyInterface & { myProp2: "foo2" };

type Identity<T> = T;
type SomeMappedType<T> = Identity<{ [k in keyof T] : [T[k]] }>

interface Bar {
  bar<T extends FooInterface & Foo2Interface>(t: T, m : SomeMappedType<T>): void;
}

class Impl implements Bar {
bar<T extends MyInterface&{ myProp: "foo"; }&{ myProp2: "foo2"; }>(t: T,m: { [k in keyof T]: [T[k]]; }): void {
throw new Error("Method not implemented.");
}
  
}

Playground

For my use case, I expected,

    replaceMany<TableT extends InsertableTable & DeletableTable> (
        table : TableT,
        rows : readonly [BuiltInInsertRow<TableT>, ...BuiltInInsertRow<TableT>[]]
    ) : Promise<ReplaceManyResult>;

But got,

replaceMany<TableT extends tsql.ITable<tsql.TableData> & {insertEnabled: true;} & {deleteEnabled: true;}>(table: TableT, rows: readonly [{readonly [columnAlias in Exclude<TableT["columns"] extends tsql.ColumnMap ? Extract<keyof TableT["columns"], string> : never, TableT["generatedColumns"][number] | TableT["nullableColumns"][number] | TableT["explicitDefaultValueColumns"][number] | TableT["autoIncrement"]>]: tsql.BuiltInExpr_NonCorrelated<ReturnType<TableT["columns"][columnAlias]["mapper"]>>;} & {readonly [columnAlias in tsql.TableUtil.OptionalColumnAlias<TableT>]?: tsql.BuiltInExpr_NonCorrelatedOrUndefined<ReturnType<TableT["columns"][columnAlias]["mapper"]>>;}, ...({readonly [columnAlias in Exclude<TableT["columns"] extends tsql.ColumnMap ? Extract<keyof TableT["columns"], string> : never, TableT["generatedColumns"][number] | TableT["nullableColumns"][number] | TableT["explicitDefaultValueColumns"][number] | TableT["autoIncrement"]>]: tsql.BuiltInExpr_NonCorrelated<ReturnType<TableT["columns"][columnAlias]["mapper"]>>;} & {readonly [columnAlias in tsql.TableUtil.OptionalColumnAlias<TableT>]?: tsql.BuiltInExpr_NonCorrelatedOrUndefined<ReturnType<TableT["columns"][columnAlias]["mapper"]>>;})[]]): Promise<tsql.ReplaceManyResult> {

Daniel Imms (@Tyriar)

Seems Daniel Imms (@Tyriar)'s original example is fixed in TS 3.7.5

AnyhowStep's example still expands the types

Closing language service bugs related to the 6.0 implementation. For more information, see #62827

Looks like the implement interface quick fix hasn't been ported yet. Opened microsoft/typescript-go#2280 to track this

Navigation Menu

Repository navigation

Filling in an implementation using VS Code will expand types #15562

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Filling in an implementation using VS Code will expand types #15562

Description

Activity

aozgaa commented on Jun 28, 2017

AnyhowStep commented on Jan 20, 2020

mjbvz commented on Jan 29, 2020

RyanCavanaugh commented on Dec 3, 2025

mjbvz commented on Dec 8, 2025

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions