feat: Support inferring config from eslint-plugin-prettier

If the eslint rule `prettier/prettier` is configured with an object we use those options for config inference and stop there.

src/__tests__/utils.js

@@ -146,6 +146,15 @@ const getPrettierOptionsFromESLintRulesTests = [
     },
     options: { arrowParens: "avoid" }
   },
+  {
+    rules: {
+      "prettier/prettier": [2, { singleQuote: false }],
+      quotes: [2, "single"]
+    },
+    options: {
+      singleQuote: false
+    }
+  },
 
   // If an ESLint rule is disabled fall back to prettier defaults.
   { rules: { "max-len": [0, { code: 120 }] }, options: {} },

src/utils.js

@@ -6,6 +6,10 @@ import getLogger from "loglevel-colored-level-prefix";
 const logger = getLogger({ prefix: "prettier-eslint" });
 const RULE_DISABLED = {};
 const RULE_NOT_CONFIGURED = "RULE_NOT_CONFIGURED";
+const ruleValueExists = prettierRuleValue =>
+  prettierRuleValue !== RULE_NOT_CONFIGURED &&
+  prettierRuleValue !== RULE_DISABLED &&
+  typeof prettierRuleValue !== "undefined";
 const OPTION_GETTERS = {
   printWidth: {
     ruleValue: rules => getRuleValue(rules, "max-len", "code"),
@@ -131,6 +135,12 @@ function getPrettierOptionsFromESLintRules(
 ) {
   const { rules } = eslintConfig;
 
+  const prettierPluginOptions = getRuleValue(rules, "prettier/prettier", []);
+
+  if (ruleValueExists(prettierPluginOptions)) {
+    prettierOptions = { ...prettierPluginOptions, ...prettierOptions };
+  }
+
   return Object.keys(OPTION_GETTERS).reduce(
     (options, key) =>
       configureOptions(
@@ -364,11 +374,7 @@ function isAlways(val) {
 }
 
 function makePrettierOption(prettierRuleName, prettierRuleValue, fallbacks) {
-  if (
-    prettierRuleValue !== RULE_NOT_CONFIGURED &&
-    prettierRuleValue !== RULE_DISABLED &&
-    typeof prettierRuleValue !== "undefined"
-  ) {
+  if (ruleValueExists(prettierRuleValue)) {
     return prettierRuleValue;
   }