Explicitly encode keyof behaviors for never and unknown into getIndexType

src/compiler/checker.ts

@@ -9846,7 +9846,8 @@ namespace ts {
                 maybeTypeOfKind(type, TypeFlags.InstantiableNonPrimitive) ? getIndexTypeForGenericType(<InstantiableType | UnionOrIntersectionType>type, stringsOnly) :
                 getObjectFlags(type) & ObjectFlags.Mapped ? filterType(getConstraintTypeFromMappedType(<MappedType>type), t => !(noIndexSignatures && t.flags & (TypeFlags.Any | TypeFlags.String | TypeFlags.Number))) :
                 type === wildcardType ? wildcardType :
-                type.flags & TypeFlags.Any ? keyofConstraintType :
+                type.flags & TypeFlags.Unknown ? neverType :
+                type.flags & (TypeFlags.Any | TypeFlags.Never) ? keyofConstraintType :
                 stringsOnly ? !noIndexSignatures && getIndexInfoOfType(type, IndexKind.String) ? stringType : getLiteralTypeFromProperties(type, TypeFlags.StringLiteral) :
                 !noIndexSignatures && getIndexInfoOfType(type, IndexKind.String) ? getUnionType([stringType, numberType, getLiteralTypeFromProperties(type, TypeFlags.UniqueESSymbol)]) :
                 !noIndexSignatures && getNonEnumNumberIndexInfo(type) ? getUnionType([numberType, getLiteralTypeFromProperties(type, TypeFlags.StringLiteral | TypeFlags.UniqueESSymbol)]) :

tests/baselines/reference/complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.errors.txt

@@ -0,0 +1,85 @@
+tests/cases/compiler/complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts(33,5): error TS2322: Type '{ type: T; localChannelId: string; }' is not assignable to type 'NewChannel<ChannelOfType<T, TextChannel> | ChannelOfType<T, EmailChannel>>'.
+  Type '{ type: T; localChannelId: string; }' is not assignable to type 'Pick<ChannelOfType<T, TextChannel> | ChannelOfType<T, EmailChannel>, "type">'.
+    Types of property 'type' are incompatible.
+      Type 'T' is not assignable to type 'ChannelOfType<T, TextChannel>["type"] & ChannelOfType<T, EmailChannel>["type"]'.
+        Type '"text" | "email"' is not assignable to type 'ChannelOfType<T, TextChannel>["type"] & ChannelOfType<T, EmailChannel>["type"]'.
+          Type '"text"' is not assignable to type 'ChannelOfType<T, TextChannel>["type"] & ChannelOfType<T, EmailChannel>["type"]'.
+            Type '"text"' is not assignable to type 'ChannelOfType<T, TextChannel>["type"]'.
+              Type 'T' is not assignable to type 'ChannelOfType<T, TextChannel>["type"]'.
+                Type '"text" | "email"' is not assignable to type 'ChannelOfType<T, TextChannel>["type"]'.
+                  Type '"text"' is not assignable to type 'ChannelOfType<T, TextChannel>["type"]'.
+                    Type '"text"' is not assignable to type 'T & "text"'.
+                      Type '"text"' is not assignable to type 'T'.
+                        Type 'T' is not assignable to type 'T & "text"'.
+                          Type '"text" | "email"' is not assignable to type 'T & "text"'.
+                            Type '"text"' is not assignable to type 'T & "text"'.
+                              Type '"text"' is not assignable to type 'T'.
+                                Type 'T' is not assignable to type '"text"'.
+                                  Type '"text" | "email"' is not assignable to type '"text"'.
+                                    Type '"email"' is not assignable to type '"text"'.
+
+
+==== tests/cases/compiler/complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts (1 errors) ====
+    interface TextChannel {
+        id: string;
+        type: 'text';
+        phoneNumber: string;
+    }
+
+    interface EmailChannel {
+        id: string;
+        type: 'email';
+        addres: string;
+    }
+
+    type Channel = TextChannel | EmailChannel;
+
+    export type ChannelType = Channel extends { type: infer R } ? R : never;
+
+    type Omit<T, K extends keyof T> = Pick<
+        T,
+        ({ [P in keyof T]: P } & { [P in K]: never } & { [x: string]: never })[keyof T]
+    >;
+
+    type ChannelOfType<T extends ChannelType, A = Channel> = A extends { type: T }
+        ? A
+        : never;
+
+
+    export type NewChannel<T extends Channel> = Pick<T, 'type'> &
+        Partial<Omit<T, 'type' | 'id'>> & { localChannelId: string };
+
+
+    export function makeNewChannel<T extends ChannelType>(type: T): NewChannel<ChannelOfType<T>> {
+        const localChannelId = `blahblahblah`;
+        return { type, localChannelId };
+        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2322: Type '{ type: T; localChannelId: string; }' is not assignable to type 'NewChannel<ChannelOfType<T, TextChannel> | ChannelOfType<T, EmailChannel>>'.
+!!! error TS2322:   Type '{ type: T; localChannelId: string; }' is not assignable to type 'Pick<ChannelOfType<T, TextChannel> | ChannelOfType<T, EmailChannel>, "type">'.
+!!! error TS2322:     Types of property 'type' are incompatible.
+!!! error TS2322:       Type 'T' is not assignable to type 'ChannelOfType<T, TextChannel>["type"] & ChannelOfType<T, EmailChannel>["type"]'.
+!!! error TS2322:         Type '"text" | "email"' is not assignable to type 'ChannelOfType<T, TextChannel>["type"] & ChannelOfType<T, EmailChannel>["type"]'.
+!!! error TS2322:           Type '"text"' is not assignable to type 'ChannelOfType<T, TextChannel>["type"] & ChannelOfType<T, EmailChannel>["type"]'.
+!!! error TS2322:             Type '"text"' is not assignable to type 'ChannelOfType<T, TextChannel>["type"]'.
+!!! error TS2322:               Type 'T' is not assignable to type 'ChannelOfType<T, TextChannel>["type"]'.
+!!! error TS2322:                 Type '"text" | "email"' is not assignable to type 'ChannelOfType<T, TextChannel>["type"]'.
+!!! error TS2322:                   Type '"text"' is not assignable to type 'ChannelOfType<T, TextChannel>["type"]'.
+!!! error TS2322:                     Type '"text"' is not assignable to type 'T & "text"'.
+!!! error TS2322:                       Type '"text"' is not assignable to type 'T'.
+!!! error TS2322:                         Type 'T' is not assignable to type 'T & "text"'.
+!!! error TS2322:                           Type '"text" | "email"' is not assignable to type 'T & "text"'.
+!!! error TS2322:                             Type '"text"' is not assignable to type 'T & "text"'.
+!!! error TS2322:                               Type '"text"' is not assignable to type 'T'.
+!!! error TS2322:                                 Type 'T' is not assignable to type '"text"'.
+!!! error TS2322:                                   Type '"text" | "email"' is not assignable to type '"text"'.
+!!! error TS2322:                                     Type '"email"' is not assignable to type '"text"'.
+    }
+
+    const newTextChannel = makeNewChannel('text');
+    // This should work
+    newTextChannel.phoneNumber = '613-555-1234';
+
+    const newTextChannel2 : NewChannel<TextChannel> = makeNewChannel('text');
+    // Compare with this, which ofc works.
+    newTextChannel2.phoneNumber = '613-555-1234';
+

tests/baselines/reference/complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.js

@@ -0,0 +1,59 @@
+//// [complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts]
+interface TextChannel {
+    id: string;
+    type: 'text';
+    phoneNumber: string;
+}
+
+interface EmailChannel {
+    id: string;
+    type: 'email';
+    addres: string;
+}
+
+type Channel = TextChannel | EmailChannel;
+
+export type ChannelType = Channel extends { type: infer R } ? R : never;
+
+type Omit<T, K extends keyof T> = Pick<
+    T,
+    ({ [P in keyof T]: P } & { [P in K]: never } & { [x: string]: never })[keyof T]
+>;
+
+type ChannelOfType<T extends ChannelType, A = Channel> = A extends { type: T }
+    ? A
+    : never;
+
+
+export type NewChannel<T extends Channel> = Pick<T, 'type'> &
+    Partial<Omit<T, 'type' | 'id'>> & { localChannelId: string };
+
+
+export function makeNewChannel<T extends ChannelType>(type: T): NewChannel<ChannelOfType<T>> {
+    const localChannelId = `blahblahblah`;
+    return { type, localChannelId };
+}
+
+const newTextChannel = makeNewChannel('text');
+// This should work
+newTextChannel.phoneNumber = '613-555-1234';
+
+const newTextChannel2 : NewChannel<TextChannel> = makeNewChannel('text');
+// Compare with this, which ofc works.
+newTextChannel2.phoneNumber = '613-555-1234';
+
+
+//// [complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.js]
+"use strict";
+exports.__esModule = true;
+function makeNewChannel(type) {
+    var localChannelId = "blahblahblah";
+    return { type: type, localChannelId: localChannelId };
+}
+exports.makeNewChannel = makeNewChannel;
+var newTextChannel = makeNewChannel('text');
+// This should work
+newTextChannel.phoneNumber = '613-555-1234';
+var newTextChannel2 = makeNewChannel('text');
+// Compare with this, which ofc works.
+newTextChannel2.phoneNumber = '613-555-1234';

tests/baselines/reference/complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.symbols

@@ -0,0 +1,130 @@
+=== tests/cases/compiler/complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts ===
+interface TextChannel {
+>TextChannel : Symbol(TextChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 0, 0))
+
+    id: string;
+>id : Symbol(TextChannel.id, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 0, 23))
+
+    type: 'text';
+>type : Symbol(TextChannel.type, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 1, 15))
+
+    phoneNumber: string;
+>phoneNumber : Symbol(TextChannel.phoneNumber, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 2, 17))
+}
+
+interface EmailChannel {
+>EmailChannel : Symbol(EmailChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 4, 1))
+
+    id: string;
+>id : Symbol(EmailChannel.id, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 6, 24))
+
+    type: 'email';
+>type : Symbol(EmailChannel.type, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 7, 15))
+
+    addres: string;
+>addres : Symbol(EmailChannel.addres, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 8, 18))
+}
+
+type Channel = TextChannel | EmailChannel;
+>Channel : Symbol(Channel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 10, 1))
+>TextChannel : Symbol(TextChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 0, 0))
+>EmailChannel : Symbol(EmailChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 4, 1))
+
+export type ChannelType = Channel extends { type: infer R } ? R : never;
+>ChannelType : Symbol(ChannelType, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 12, 42))
+>Channel : Symbol(Channel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 10, 1))
+>type : Symbol(type, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 14, 43))
+>R : Symbol(R, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 14, 55))
+>R : Symbol(R, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 14, 55))
+
+type Omit<T, K extends keyof T> = Pick<
+>Omit : Symbol(Omit, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 14, 72))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 16, 10))
+>K : Symbol(K, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 16, 12))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 16, 10))
+>Pick : Symbol(Pick, Decl(lib.es5.d.ts, --, --))
+
+    T,
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 16, 10))
+
+    ({ [P in keyof T]: P } & { [P in K]: never } & { [x: string]: never })[keyof T]
+>P : Symbol(P, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 18, 8))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 16, 10))
+>P : Symbol(P, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 18, 8))
+>P : Symbol(P, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 18, 32))
+>K : Symbol(K, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 16, 12))
+>x : Symbol(x, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 18, 54))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 16, 10))
+
+>;
+
+type ChannelOfType<T extends ChannelType, A = Channel> = A extends { type: T }
+>ChannelOfType : Symbol(ChannelOfType, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 19, 2))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 21, 19))
+>ChannelType : Symbol(ChannelType, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 12, 42))
+>A : Symbol(A, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 21, 41))
+>Channel : Symbol(Channel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 10, 1))
+>A : Symbol(A, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 21, 41))
+>type : Symbol(type, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 21, 68))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 21, 19))
+
+    ? A
+>A : Symbol(A, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 21, 41))
+
+    : never;
+
+
+export type NewChannel<T extends Channel> = Pick<T, 'type'> &
+>NewChannel : Symbol(NewChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 23, 12))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 26, 23))
+>Channel : Symbol(Channel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 10, 1))
+>Pick : Symbol(Pick, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 26, 23))
+
+    Partial<Omit<T, 'type' | 'id'>> & { localChannelId: string };
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Omit : Symbol(Omit, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 14, 72))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 26, 23))
+>localChannelId : Symbol(localChannelId, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 27, 39))
+
+
+export function makeNewChannel<T extends ChannelType>(type: T): NewChannel<ChannelOfType<T>> {
+>makeNewChannel : Symbol(makeNewChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 27, 65))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 30, 31))
+>ChannelType : Symbol(ChannelType, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 12, 42))
+>type : Symbol(type, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 30, 54))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 30, 31))
+>NewChannel : Symbol(NewChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 23, 12))
+>ChannelOfType : Symbol(ChannelOfType, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 19, 2))
+>T : Symbol(T, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 30, 31))
+
+    const localChannelId = `blahblahblah`;
+>localChannelId : Symbol(localChannelId, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 31, 9))
+
+    return { type, localChannelId };
+>type : Symbol(type, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 32, 12))
+>localChannelId : Symbol(localChannelId, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 32, 18))
+}
+
+const newTextChannel = makeNewChannel('text');
+>newTextChannel : Symbol(newTextChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 35, 5))
+>makeNewChannel : Symbol(makeNewChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 27, 65))
+
+// This should work
+newTextChannel.phoneNumber = '613-555-1234';
+>newTextChannel.phoneNumber : Symbol(phoneNumber, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 2, 17))
+>newTextChannel : Symbol(newTextChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 35, 5))
+>phoneNumber : Symbol(phoneNumber, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 2, 17))
+
+const newTextChannel2 : NewChannel<TextChannel> = makeNewChannel('text');
+>newTextChannel2 : Symbol(newTextChannel2, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 39, 5))
+>NewChannel : Symbol(NewChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 23, 12))
+>TextChannel : Symbol(TextChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 0, 0))
+>makeNewChannel : Symbol(makeNewChannel, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 27, 65))
+
+// Compare with this, which ofc works.
+newTextChannel2.phoneNumber = '613-555-1234';
+>newTextChannel2.phoneNumber : Symbol(phoneNumber, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 2, 17))
+>newTextChannel2 : Symbol(newTextChannel2, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 39, 5))
+>phoneNumber : Symbol(phoneNumber, Decl(complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts, 2, 17))
+

tests/baselines/reference/complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.types

@@ -0,0 +1,96 @@
+=== tests/cases/compiler/complicatedIndexedAccessKeyofReliesOnKeyofNeverUpperBound.ts ===
+interface TextChannel {
+    id: string;
+>id : string
+
+    type: 'text';
+>type : "text"
+
+    phoneNumber: string;
+>phoneNumber : string
+}
+
+interface EmailChannel {
+    id: string;
+>id : string
+
+    type: 'email';
+>type : "email"
+
+    addres: string;
+>addres : string
+}
+
+type Channel = TextChannel | EmailChannel;
+>Channel : Channel
+
+export type ChannelType = Channel extends { type: infer R } ? R : never;
+>ChannelType : "text" | "email"
+>type : R
+
+type Omit<T, K extends keyof T> = Pick<
+>Omit : Pick<T, ({ [P in keyof T]: P; } & { [P in K]: never; } & { [x: string]: never; })[keyof T]>
+
+    T,
+    ({ [P in keyof T]: P } & { [P in K]: never } & { [x: string]: never })[keyof T]
+>x : string
+
+>;
+
+type ChannelOfType<T extends ChannelType, A = Channel> = A extends { type: T }
+>ChannelOfType : ChannelOfType<T, A>
+>type : T
+
+    ? A
+    : never;
+
+
+export type NewChannel<T extends Channel> = Pick<T, 'type'> &
+>NewChannel : NewChannel<T>
+
+    Partial<Omit<T, 'type' | 'id'>> & { localChannelId: string };
+>localChannelId : string
+
+
+export function makeNewChannel<T extends ChannelType>(type: T): NewChannel<ChannelOfType<T>> {
+>makeNewChannel : <T extends "text" | "email">(type: T) => NewChannel<ChannelOfType<T, TextChannel> | ChannelOfType<T, EmailChannel>>
+>type : T
+
+    const localChannelId = `blahblahblah`;
+>localChannelId : "blahblahblah"
+>`blahblahblah` : "blahblahblah"
+
+    return { type, localChannelId };
+>{ type, localChannelId } : { type: T; localChannelId: string; }
+>type : T
+>localChannelId : string
+}
+
+const newTextChannel = makeNewChannel('text');
+>newTextChannel : NewChannel<TextChannel>
+>makeNewChannel('text') : NewChannel<TextChannel>
+>makeNewChannel : <T extends "text" | "email">(type: T) => NewChannel<ChannelOfType<T, TextChannel> | ChannelOfType<T, EmailChannel>>
+>'text' : "text"
+
+// This should work
+newTextChannel.phoneNumber = '613-555-1234';
+>newTextChannel.phoneNumber = '613-555-1234' : "613-555-1234"
+>newTextChannel.phoneNumber : string
+>newTextChannel : NewChannel<TextChannel>
+>phoneNumber : string
+>'613-555-1234' : "613-555-1234"
+
+const newTextChannel2 : NewChannel<TextChannel> = makeNewChannel('text');
+>newTextChannel2 : NewChannel<TextChannel>
+>makeNewChannel('text') : NewChannel<TextChannel>
+>makeNewChannel : <T extends "text" | "email">(type: T) => NewChannel<ChannelOfType<T, TextChannel> | ChannelOfType<T, EmailChannel>>
+>'text' : "text"
+
+// Compare with this, which ofc works.
+newTextChannel2.phoneNumber = '613-555-1234';
+>newTextChannel2.phoneNumber = '613-555-1234' : "613-555-1234"
+>newTextChannel2.phoneNumber : string
+>newTextChannel2 : NewChannel<TextChannel>
+>phoneNumber : string
+>'613-555-1234' : "613-555-1234"
+