Adding type inference and makeT helper function

app/client/lib/localization.ts

@@ -80,11 +80,15 @@ export function tString(key: string, args?: any, instance = i18next): string {
   return instance.t(key, args);
 }
 
+// We will try to infer result from the arguments passed to `t` function.
+// For plain objects we expect string as a result. If any property doesn't look as a plain value
+// we assume that it might be a dom node and the result is DomContents.
+type InferResult<T> = T extends Record<string, string | number | boolean>|undefined|null ? string : DomContents;
 
 /**
  * Resolves the translation of the given key and substitutes. Supports dom elements interpolation.
  */
- export function t(key: string, args?: any, instance = i18next): DomContents {
+ export function t<T extends Record<string, any>>(key: string, args?: T|null, instance = i18next): InferResult<T> {
   if (!instance.exists(key, args || undefined)) {
     const error = new Error(`Missing translation for key: ${key} and language: ${i18next.language}`);
     reportError(error);
@@ -92,7 +96,7 @@ export function tString(key: string, args?: any, instance = i18next): string {
   // If there are any DomElements in args, handle it with missingInterpolationHandler.
   const domElements = !args ? [] : Object.entries(args).filter(([_, value]) => isLikeDomContents(value));
   if (!args || !domElements.length) {
-    return instance.t(key, args || undefined) as string;
+    return instance.t(key, args || undefined) as any;
   } else {
     // Make a copy of the arguments, and remove any dom elements from it. It will instruct
     // i18next library to use `missingInterpolationHandler` handler.
@@ -110,7 +114,7 @@ export function tString(key: string, args?: any, instance = i18next): string {
       const domElement = args[propName] ?? `{{${propName}}}`; // If the prop is not there, simulate default behavior.
       parts[i] = domElement;
     }
-    return parts;
+    return parts.filter(p => p !== '') as any; // Remove empty parts.
   }
 }
 
@@ -135,3 +139,12 @@ function isLikeDomContents(value: any): boolean {
     (Array.isArray(value) && isLikeDomContents(value[0])) || // DomComputed
     typeof value === 'function'; // DomMethod
 }
+
+/**
+ * Helper function to create scoped t function.
+ */
+export function makeT(scope: string) {
+  return function<T extends Record<string, any>>(key: string, args?: T|null, instance = i18next) {
+    return t(`${scope}.${key}`, args, instance);
+  }
+}

app/client/ui/AddNewButton.ts

@@ -1,9 +1,9 @@
 import {theme, vars} from 'app/client/ui2018/cssVars';
+import {makeT} from 'app/client/lib/localization';
 import {icon} from 'app/client/ui2018/icons';
 import {dom, DomElementArg, Observable, styled} from "grainjs";
-import {t} from 'app/client/lib/localization';
 
-const translate = (x: string, args?: any) => t(`AddNewButton.${x}`, args);
+const translate = makeT(`AddNewButton`);
 
 export function addNewButton(isOpen: Observable<boolean> | boolean = true, ...args: DomElementArg[]) {
   return cssAddNewButton(

app/client/ui/DocMenu.ts

@@ -29,12 +29,12 @@ import {Document, Workspace} from 'app/common/UserAPI';
 import {computed, Computed, dom, DomArg, DomContents, IDisposableOwner,
         makeTestId, observable, Observable} from 'grainjs';
 import {buildTemplateDocs} from 'app/client/ui/TemplateDocs';
-import {t} from 'app/client/lib/localization';
+import {makeT} from 'app/client/lib/localization';
 import {localStorageBoolObs} from 'app/client/lib/localStorageObs';
 import {bigBasicButton} from 'app/client/ui2018/buttons';
 import sortBy = require('lodash/sortBy');
 
-const translate = (x: string, args?: any) => t(`DocMenu.${x}`, args);
+const translate = makeT(`DocMenu`);
 
 const testId = makeTestId('test-dm-');
 

app/client/ui/HomeIntro.ts

@@ -1,4 +1,4 @@
-import {t} from 'app/client/lib/localization';
+import {makeT} from 'app/client/lib/localization';
 import {getLoginOrSignupUrl, urlState} from 'app/client/models/gristUrlState';
 import {HomeModel} from 'app/client/models/HomeModel';
 import {productPill} from 'app/client/ui/AppHeader';
@@ -14,7 +14,7 @@ import {FullUser} from 'app/common/LoginSessionAPI';
 import * as roles from 'app/common/roles';
 import {Computed, dom, DomContents, styled} from 'grainjs';
 
-const translate = (x: string, args?: any) => t(`HomeIntro.${x}`, args);
+const translate = makeT('HomeIntro');
 
 export function buildHomeIntro(homeModel: HomeModel): DomContents {
   const isViewer = homeModel.app.currentOrg?.access === roles.VIEWER;
@@ -103,7 +103,7 @@ function makePersonalIntro(homeModel: HomeModel, user: FullUser) {
     css.docListHeader(`Welcome to Grist, ${user.name}!`, testId('welcome-title')),
     cssIntroLine('Get started by creating your first Grist document.'),
     (shouldHideUiElement('helpCenter') ? null :
-      cssIntroLine(t('HomeIntro.VisitHelpCenter', { link: helpCenterLink() }),
+      cssIntroLine(translate('VisitHelpCenter', { link: helpCenterLink() }),
         testId('welcome-text'))
     ),
     makeCreateButtons(homeModel),
@@ -116,7 +116,7 @@ function makeAnonIntro(homeModel: HomeModel) {
     css.docListHeader(translate('Welcome'), testId('welcome-title')),
     cssIntroLine('Get started by exploring templates, or creating your first Grist document.'),
     cssIntroLine(signUp, ' to save your work. ',
-      (shouldHideUiElement('helpCenter') ? null : t('HomeIntro.VisitHelpCenter', { link: helpCenterLink() })),
+      (shouldHideUiElement('helpCenter') ? null : translate('VisitHelpCenter', { link: helpCenterLink() })),
       testId('welcome-text')),
     makeCreateButtons(homeModel),
   ];