feat: 🎸 add "transpileOnly" option to skip type check

Issues: #54

Author: kaisermann

Diff for: README.md

@@ -377,6 +377,12 @@ const options = {
     compilerOptions: {
       module: 'es2015',
     },
+
+    /**
+     * Type checking can be skipped by setting 'transpileOnly: true'.
+     * This speeds up your build process.
+     */
+    transpileOnly: true,
   },
 
   /** Use a custom preprocess method by passing a function. */
@@ -422,3 +428,25 @@ ul
 ![image](https://user-images.githubusercontent.com/2388078/63219174-8d4d8b00-c129-11e9-9fb0-56260a125155.png)
 
 If you have configured `svelte-preprocess` to use some kind of preprocessor and `svelte-vscode` is displaying errors like it's ignoring your preprocess configuration, that's happening because `svelte-vscode` needs to know how to preprocess your components. `svelte-vscode` works by having a svelte compiler running on the background and you can configure it by [creating a `svelte.config.js`](#with-svelte-vs-code) file on your project's root. Please check this document [With Svelte VS Code](#with-svelte-vs-code) section.
+
+### My `typescript` compilation is sloooooooow
+
+If you have a medium-to-big project, the typescript processor might start to get slow. If you already have an IDE type checking your code, you can speed up the transpilation process by setting `transpileOnly` to `true`:
+
+```js
+const preprocess = require('svelte-preprocess')
+...
+{
+  ...svelteOptions,
+  preprocess: preprocess({
+    typescript: {
+      // skips type checking
+      transpileOnly: true,
+      compilerOptions: {
+        ...
+      },
+    },
+  })
+}
+...
+```

Diff for: src/transformers/typescript.js

@@ -195,10 +195,23 @@ module.exports = ({ content, filename, options }) => {
     allowNonTsExtensions: true,
   }
 
-  const { code, map, diagnostics } = compileFileFromMemory(compilerOptions, {
-    filename,
-    content,
-  })
+  let code, map, diagnostics
+  if (options.transpileOnly || compilerOptions.transpileOnly) {
+    ;({
+      outputText: code,
+      sourceMapText: map,
+      diagnostics,
+    } = ts.transpileModule(content, {
+      fileName: filename,
+      compilerOptions: compilerOptions,
+      reportDiagnostics: options.reportDiagnostics !== false,
+    }))
+  } else {
+    ;({ code, map, diagnostics } = compileFileFromMemory(compilerOptions, {
+      filename,
+      content,
+    }))
+  }
 
   if (diagnostics.length > 0) {
     // could this be handled elsewhere?

Diff for: test/transformers/typescript.test.js

@@ -69,6 +69,19 @@ describe('transformer - typescript', () => {
       })
       return expect(preprocess(template, opts)).rejects.toThrow('TS6046')
     })
+
+    it('should not type check if "transpileOnly: true"', async () => {
+      const opts = getAutoPreprocess({
+        typescript: {
+          transpileOnly: true,
+          compilerOptions: {
+            module: 'ESNext',
+          },
+        },
+      })
+      const { code } = await preprocess(template, opts)
+      return expect(code).toContain(getFixtureContent('script.js'))
+    })
   })
 
   describe('code errors', () => {