Remove duplication from exhaustiveness checks for discriminating unions

Co-authored-by: Mikko Aspiala <mikko.aspiala@gmail.com>

Signed-off-by: Janne Savolainen <janne.savolainen@live.fi>

src/common/utils/composable-responsibilities/discriminable/discriminable.ts

@@ -5,3 +5,13 @@
 
 // See: https://www.typescriptlang.org/docs/handbook/unions-and-intersections.html#discriminating-unions
 export interface Discriminable<T extends string> { kind: T }
+
+// Note: this will fail at transpilation time, if all kinds are not instructed in switch/case.
+// See: https://www.typescriptlang.org/docs/handbook/2/narrowing.html#exhaustiveness-checking
+export const checkThatAllDiscriminablesAreExhausted = <T extends never>(value: T) => {
+  const _exhaustiveCheck: never = value;
+
+  return new Error(
+    `Tried to exhaust discriminables, but no instructions were found for ${(_exhaustiveCheck as any).kind}`,
+  );
+};

src/features/application-menu/main/populate-application-menu.injectable.ts

@@ -10,6 +10,7 @@ import type { ApplicationMenuItemTypes } from "./menu-items/application-menu-ite
 import { pipeline } from "@ogre-tools/fp";
 import { map, sortBy } from "lodash/fp";
 import type { MenuItemRoot } from "./application-menu-item-composite.injectable";
+import { checkThatAllDiscriminablesAreExhausted } from "../../../common/utils/composable-responsibilities/discriminable/discriminable";
 
 const populateApplicationMenuInjectable = getInjectable({
   id: "populate-application-menu",
@@ -32,12 +33,12 @@ export default populateApplicationMenuInjectable;
 const toHierarchicalElectronMenuItem = (
   composite: Composite<ApplicationMenuItemTypes>,
 ): MenuItemOpts => {
-  switch (composite.value.kind) {
+  const value = composite.value;
+
+  switch (value.kind) {
     case "top-level-menu": {
-      const {
+      const { id } = composite;
-        id,
+      const { label, role } = value;
-        value: { label, role },
-      } = composite;
 
       return {
         ...(id ? { id } : {}),
@@ -53,10 +54,8 @@ const toHierarchicalElectronMenuItem = (
     }
 
     case "sub-menu": {
-      const {
+      const { id } = composite;
-        id,
+      const { label } = value;
-        value: { label },
-      } = composite;
 
       return {
         ...(id ? { id } : {}),
@@ -71,10 +70,8 @@ const toHierarchicalElectronMenuItem = (
     }
 
     case "clickable-menu-item": {
-      const {
+      const { id } = composite;
-        id,
+      const { label, onClick, keyboardShortcut } = value;
-        value: { label, onClick, keyboardShortcut },
-      } = composite;
 
       return {
         ...(id ? { id } : {}),
@@ -85,9 +82,7 @@ const toHierarchicalElectronMenuItem = (
     }
 
     case "os-action-menu-item": {
-      const {
+      const { label, keyboardShortcut, actionName } = value;
-        value: { label, keyboardShortcut, actionName },
-      } = composite;
 
       return {
         ...(label ? { label } : {}),
@@ -103,14 +98,7 @@ const toHierarchicalElectronMenuItem = (
     }
 
     default: {
-      // Note: this will fail at transpilation time, if all ApplicationMenuItemTypes
+      throw checkThatAllDiscriminablesAreExhausted(value);
-      // are not handled in switch/case.
-      const _exhaustiveCheck: never = composite.value;
-
-      // Note: this code is unreachable, it is here to make ts not complain about
-      // _exhaustiveCheck not being used.
-      // See: https://www.typescriptlang.org/docs/handbook/2/narrowing.html#exhaustiveness-checking
-      throw new Error(`Tried to create application menu, but foreign menu item was encountered: ${_exhaustiveCheck} ${composite.value}`);
     }
   }
 };

src/features/preferences/renderer/preference-navigation/preferences-navigation.tsx

@@ -15,6 +15,7 @@ import { PreferencesNavigationTab } from "./preferences-navigation-tab";
 import { compositeHasDescendant } from "../../../../common/utils/composite/composite-has-descendant/composite-has-descendant";
 import type { PreferenceTabsRoot } from "../preference-items/preference-tab-root";
 import { Icon } from "../../../../renderer/components/icon";
+import { checkThatAllDiscriminablesAreExhausted } from "../../../../common/utils/composable-responsibilities/discriminable/discriminable";
 
 interface Dependencies {
   composite: IComputedValue<Composite<PreferenceTypes | PreferenceTabsRoot>>;
@@ -88,16 +89,7 @@ const toNavigationHierarchy = (composite: Composite<PreferenceTypes | Preference
     }
 
     default: {
-      // Note: this will fail at transpilation time, if all kinds
+      throw checkThatAllDiscriminablesAreExhausted(value);
-      // are not handled in switch/case.
-      const _exhaustiveCheck: never = value;
-
-      // Note: this code is unreachable, it is here to make ts not complain about
-      // _exhaustiveCheck not being used.
-      // See: https://www.typescriptlang.org/docs/handbook/2/narrowing.html#exhaustiveness-checking
-      throw new Error(
-        `Tried to create preference navigation, but foreign item was encountered: ${_exhaustiveCheck} ${composite.value}`,
-      );
     }
   }
 };
@@ -108,3 +100,4 @@ const hasContent = compositeHasDescendant<PreferenceTypes | PreferenceTabsRoot>(
 
 const emptyRender = <></>;
 
+

src/features/preferences/renderer/preferences.tsx

@@ -16,6 +16,7 @@ import { Map } from "../../../renderer/components/map/map";
 import { observer } from "mobx-react";
 import { PreferencesNavigation } from "./preference-navigation/preferences-navigation";
 import Gutter from "../../../renderer/components/gutter/gutter";
+import { checkThatAllDiscriminablesAreExhausted } from "../../../common/utils/composable-responsibilities/discriminable/discriminable";
 
 interface Dependencies {
   closePreferences: () => void;
@@ -94,16 +95,7 @@ const toPreferenceItemHierarchy = (composite: Composite<PreferenceTypes>) => {
     }
 
     default: {
-      // Note: this will fail at transpilation time, if all kinds
+      throw checkThatAllDiscriminablesAreExhausted(value);
-      // are not handled in switch/case.
-      const _exhaustiveCheck: never = value;
-
-      // Note: this code is unreachable, it is here to make ts not complain about
-      // _exhaustiveCheck not being used.
-      // See: https://www.typescriptlang.org/docs/handbook/2/narrowing.html#exhaustiveness-checking
-      throw new Error(
-        `Tried to create preferences, but foreign item was encountered: ${_exhaustiveCheck} ${value}`,
-      );
     }
   }
 };