feat: 🎸 support prependData for almost every preprocessor

BREAKING CHANGE: 🧨 This is a general evolution of the specific `scss.data` property that
was used to prepend data to components written in scss.
`{preprocessorOptions}.prependData` is now the way to prepend some
string to any preprocessor.

Author: kaisermann

Diff for: README.md

@@ -26,13 +26,13 @@
   - [Standalone processors](#standalone-processors)
 - [Options](#options)
 - [Specifics and limitations](#specifics-and-limitations)
+  - [General](#general)
   - [`scss`/`sass`](#scsssass)
   - [`typescript`](#typescript)
   - [`pug`](#pug)
   - [`coffeescript`](#coffeescript)
 - [FAQ](#faq)
   - [My VS Code is displaying a lot of errors on my templates when I try to use `x`...](#my-vs-code-is-displaying-a-lot-of-errors-on-my-templates-when-i-try-to-use-x)
-  - [My `typescript` compilation is sloooooooow](#my-typescript-compilation-is-sloooooooow)
 
 <!-- /code_chunk_output -->
 
@@ -544,11 +544,33 @@ svelte.preprocess(input, sveltePreprocess(options));
 
 ## Specifics and limitations
 
+### General
+
+#### Prepending data
+
+For almost language, `svelte-preprocess` accepts a `prependData` property that allows to prepend any string content to your component's `style` or `script` sections.
+
+```js
+import preprocess from 'svelte-preprocess'
+
+expor default {
+  ...,
+  preprocess: preprocess({
+    scss: {
+      prependData: `@use theme`
+    },
+    javascript: {
+      prependData: `import { _ } from 'svelte-i18n'`
+    }
+  }),
+  ...
+}
+```
+
 ### `scss`/`sass`
 
 The SCSS/SASS processor accepts the default sass options alongside two other props:
 
-- `data: string` - a string prepended to every scss file processed.
 - `renderSync: boolean` - if `true`, use the sync render method which is faster for dart sass.
 - `implementation: object` - pass the module to use to compile sass, if unspecified, `svelte-preprocess` will first look for `node-sass` and then for `sass`.
 

Diff for: src/autoProcess.ts

@@ -1,5 +1,3 @@
-import stripIndent from 'strip-indent';
-
 import {
   PreprocessorGroup,
   Preprocessor,
@@ -11,9 +9,10 @@ import {
 } from './types';
 import { hasDepInstalled } from './modules/hasDepInstalled';
 import { concat } from './modules/concat';
-import { parseFile } from './modules/parseFile';
+import { getTagInfo } from './modules/tagInfo';
 import { addLanguageAlias, getLanguageFromAlias } from './modules/language';
 import { throwError } from './modules/errors';
+import { prepareContent } from './modules/prepareContent';
 
 type AutoPreprocessOptions = {
   markupTagName?: string;
@@ -61,9 +60,6 @@ export const runTransformer = async (
     return { code: content };
   }
 
-  // remove any unnecessary indentation (useful for coffee, pug and sugarss)
-  content = stripIndent(content);
-
   if (typeof options === 'function') {
     return options({ content, map, filename, attributes });
   }
@@ -149,26 +145,33 @@ export function autoPreprocess(
       alias,
       dependencies,
       attributes,
-    } = await parseFile(svelteFile);
+    } = await getTagInfo(svelteFile);
 
     if (lang == null || alias == null) {
       alias = defaultLanguages[type];
       lang = getLanguageFromAlias(alias);
     }
 
     if (preserve.includes(lang) || preserve.includes(alias)) {
-      return;
+      return { code: content };
     }
 
+    const transformerOptions = getTransformerOptions(lang, alias);
+
+    content = prepareContent({
+      options: transformerOptions,
+      content,
+    });
+
     if (lang === targetLanguage) {
       return { code: content, dependencies };
     }
 
-    const transformed = await runTransformer(
-      lang,
-      getTransformerOptions(lang, alias),
-      { content: stripIndent(content), filename, attributes },
-    );
+    const transformed = await runTransformer(lang, transformerOptions, {
+      content,
+      filename,
+      attributes,
+    });
 
     return {
       ...transformed,
@@ -235,8 +238,6 @@ export function autoPreprocess(
         filename,
       });
 
-      if (transformResult == null) return;
-
       let { code, map, dependencies, diagnostics } = transformResult;
 
       if (transformers.babel) {
@@ -262,8 +263,6 @@ export function autoPreprocess(
         filename,
       });
 
-      if (transformResult == null) return;
-
       let { code, map, dependencies } = transformResult;
 
       if (await hasDepInstalled('postcss')) {

Diff for: src/modules/prepareContent.ts

@@ -0,0 +1,21 @@
+import stripIndent from 'strip-indent';
+
+export function prepareContent({
+  options,
+  content,
+}: {
+  options: any;
+  content: string;
+}) {
+  if (typeof options !== 'object') {
+    return content;
+  }
+
+  content = stripIndent(content);
+
+  if (options?.prependData) {
+    content = `${options.prependData}\n${content}`;
+  }
+
+  return content;
+}

Diff for: src/modules/parseFile.ts renamed to src/modules/tagInfo.ts

@@ -4,10 +4,10 @@ import { resolve, dirname } from 'path';
 import { PreprocessorArgs } from '../types';
 import { getLanguage } from './language';
 
-export const resolveSrc = (importerFile: string, srcPath: string) =>
+const resolveSrc = (importerFile: string, srcPath: string) =>
   resolve(dirname(importerFile), srcPath);
 
-export const getSrcContent = (file: string): Promise<string> => {
+const getSrcContent = (file: string): Promise<string> => {
   return new Promise((resolve, reject) => {
     readFile(file, (error: Error, data: unknown) => {
       // istanbul ignore if
@@ -21,7 +21,7 @@ async function doesFileExist(file: string) {
   return new Promise((resolve) => access(file, 0, (err) => resolve(!err)));
 }
 
-export const parseFile = async ({
+export const getTagInfo = async ({
   attributes,
   filename,
   content,