tools: add lint fixer for `require-buffer`

Adds `require-buffer` lint fixer.
If the buffer module is not required while `Buffer` is used, require the `buffer` module.
If the file has a `'use strict';` line, add the require after it on a separate line.
If the file does not have any (currently impossible with the `strict` rule) add it after the first comment (before the real code starts).

Fixes: https://github.com/nodejs/node/issues/16636
PR-URL: https://github.com/nodejs/node/pull/17144
Reviewed-By: Michaël Zasso <targos@protonmail.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/tools/eslint-rules/require-buffer.js b/tools/eslint-rules/require-buffer.js
index c9818cb758..c6040b43a1 100644
--- a/tools/eslint-rules/require-buffer.js
+++ b/tools/eslint-rules/require-buffer.js
@@ -1,10 +1,26 @@
 'use strict';
+const BUFFER_REQUIRE = 'const { Buffer } = require(\'buffer\');\n';
 
 module.exports = function(context) {
+
   function flagIt(reference) {
     const msg = 'Use const Buffer = require(\'buffer\').Buffer; ' +
                 'at the beginning of this file';
-    context.report(reference.identifier, msg);
+
+    context.report({
+      node: reference.identifier,
+      message: msg,
+      fix: (fixer) => {
+        const sourceCode = context.getSourceCode();
+
+        const useStrict = /'use strict';\n\n?/g;
+        const hasUseStrict = !!useStrict.exec(sourceCode.text);
+        const firstLOC = sourceCode.ast.range[0];
+        const rangeNeedle = hasUseStrict ? useStrict.lastIndex : firstLOC;
+
+        return fixer.insertTextBeforeRange([rangeNeedle], BUFFER_REQUIRE);
+      }
+    });
   }
 
   return {