Improved TypeScript 3.7 Support

[arabold]

I was running into an issue using TypeScript 3.7 with optional chaining and React Fragments using empty tags (<>...</>). In order to get both working properly the TypeScript preprocessor needs some minimal changes:

diff --git a/node_modules/i18n-tag-schema/dist/lib/preprocessors/typescript.js b/node_modules/i18n-tag-schema/dist/lib/preprocessors/typescript.js
index 0e5cd94..60923e3 100644
--- a/node_modules/i18n-tag-schema/dist/lib/preprocessors/typescript.js
+++ b/node_modules/i18n-tag-schema/dist/lib/preprocessors/typescript.js
@@ -15,8 +15,8 @@ exports.default = function (contents, filePath) {
   if (!ts) throw new Error('cannot find typescript compiler. check if \'typescript\' node module is installed.');
   var processed = ts.transpileModule(contents, {
     compilerOptions: {
-      target: ts.ScriptTarget.Latest,
-      jsx: path.extname(filePath) !== '.ts' ? ts.JsxEmit.Preserve : ts.JsxEmit.None
+      target: ts.ScriptTarget.ES2020,
+      jsx: path.extname(filePath) !== '.ts' ? ts.JsxEmit.React : ts.JsxEmit.None
     }
   });
   if (processed && processed.outputText) {

By setting ES2020 we force transpiling optional chaining syntax (such as foo?.bar and foo ?? bar). ts.JsxEmit.React is needed for proper fragment support.

[skolmer]

Thank you for your contribution!

I don't want to enable ES2020 for the default preprocessor because it is still a draft. But you could release your preprocessor as an npm package with more sophisticated features and configurations.
https://github.com/skolmer/i18n-tag-schema#-preprocessors
I could add a link to your npm package to the readme of this repository.

The preprocessor that comes out of the box is really just a basic implementation for starters and to show what's possible with this library.