fix(types): type translation variable keys

Signed-off-by: Grigorii K. Shartsev <me@shgk.me>

lib/translation.ts

@@ -31,8 +31,17 @@ interface TranslationVariableReplacementObject<T> {
  escape: boolean
 }
 
+/**
+ * Extracts variables from a translation key
+ * @notExported
+ */
+type ExtractedVariables<T extends string> =
+ T extends `${string}{${infer Variable}}${infer Rest}`
+ ? Variable | ExtractedVariables<Rest>
+ : never
+
 /** @notExported */
-type TranslationVariables = Record<string, string | number | TranslationVariableReplacementObject<string | number>>
+type TranslationVariables<K extends string> = Record<ExtractedVariables<K>, string | number | TranslationVariableReplacementObject<string | number>>
 
 /**
  * Translate a string
@@ -47,10 +56,10 @@ type TranslationVariables = Record<string, string | number | TranslationVariable
  *
  * @return {string}
  */
-export function translate(
+export function translate<T extends string>(
  app: string,
- text: string,
- vars?: TranslationVariables,
+ text: T,
+ vars?: TranslationVariables<T>,
  number?: number,
  options?: TranslationOptions,
 ): string {
@@ -71,7 +80,7 @@ export function translate(
  // TODO: cache this function to avoid inline recreation
  // of the same function over and over again in case
  // translate() is used in a loop
- const _build = (text: string, vars?: TranslationVariables, number?: number) => {
+ const _build = (text: string, vars?: TranslationVariables<T>, number?: number) => {
  return text.replace(/%n/g, '' + number).replace(/{([^{}]*)}/g, (match, key) => {
  if (vars === undefined || !(key in vars)) {
  return optEscape(match)
@@ -119,12 +128,12 @@ export function translate(
  * @param {object} vars of placeholder key to value
  * @param {object} options options object
  */
-export function translatePlural(
+export function translatePlural<T extends string, K extends string, >(
  app: string,
- textSingular: string,
- textPlural: string,
+ textSingular: T,
+ textPlural: K,
  number: number,
- vars?: Record<string, string | number>,
+ vars?: TranslationVariables<T> & TranslationVariables<K>,
  options?: TranslationOptions,
 ): string {
  const identifier = '_' + textSingular + '_::_' + textPlural + '_'
@@ -139,10 +148,11 @@ export function translatePlural(
  }
  }
 
+ // vars type is casted to allow extra keys without runtime filtering (they are harmless), and without allowing wrong keys in translate
  if (number === 1) {
- return translate(app, textSingular, vars, number, options)
+ return translate(app, textSingular, vars as TranslationVariables<T>, number, options)
  } else {
- return translate(app, textPlural, vars, number, options)
+ return translate(app, textPlural, vars as TranslationVariables<K>, number, options)
  }
 }