Fix: avoid relying on an internal eslint function

.eslintrc.js

@@ -23,6 +23,7 @@ module.exports = {
     'eslint-plugin/report-message-format': ['error', '^[^a-z].*\\.$'],
     'array-bracket-spacing': 'off',
     'comma-dangle': 'off',
+    indent: 'off',
     'lines-around-directive': 'off',
     'space-before-function-paren': 'off'
   }

lib/rules/prettier.js

@@ -6,7 +6,6 @@
 
 const util = require('util');
 const prettier = require('prettier');
-const astUtils = require('eslint/lib/ast-utils');
 
 // ------------------------------------------------------------------------------
 // Rule Definition
@@ -16,6 +15,23 @@ module.exports = {
   create(context) {
     const sourceCode = context.getSourceCode();
 
+    /**
+     * Gets the location of a given index in the source code
+     * @param {number} index An index in the source code
+     * @returns {object} An object containing numberic `line` and `column` keys
+     */
+    function getLocation(index) {
+      // If sourceCode.getLocFromIndex is available from eslint, use it.
+      // Otherwise, use the private version from eslint/lib/ast-utils.
+
+      return sourceCode.getLocFromIndex
+        ? sourceCode.getLocFromIndex(index)
+        : require('eslint/lib/ast-utils').getLocationFromRangeIndex(
+            sourceCode,
+            index
+          );
+    }
+
     return {
       Program() {
         // This isn't really very performant (prettier needs to reparse the text).
@@ -40,8 +56,7 @@ module.exports = {
                 : sourceCode.text[firstBadIndex];
 
           context.report({
-            loc: astUtils.getLocationFromRangeIndex(
-              sourceCode,
+            loc: getLocation(
               firstBadIndex === -1 ? desiredText.length : firstBadIndex
             ),
             message: 'Follow `prettier` formatting (expected {{expectedChar}} but found {{foundChar}}).',