fix: specify config file correctly

`overrides` field in config file  did not work in the original implementation

BREAKING CHANGE:

- specify config file via filepath instead of directory

README.md

@@ -82,13 +82,13 @@ If there is no option provided, it'll try to load [config file](https://prettier
 }
 ```
 
-If you'd like to specify where to find the config file, just put the search path (relative to `process.cwd()`) in the second argument, the following example shows how to use the config file from `<cwd>/configs/.prettierrc`:
+If you'd like to specify which config file to use, just put its path (relative to `process.cwd()`) in the second argument, the following example shows how to load the config file from `<cwd>/configs/.prettierrc`:
 
 ```json
 {
   "extends": ["tslint-plugin-prettier"],
   "rules": {
-    "prettier": [true, "configs"]
+    "prettier": [true, "configs/.prettierrc"]
   }
 }
 ```

src/prettierRule.ts

@@ -23,12 +23,19 @@ class Walker extends tslint.AbstractWalker<any[]> {
         options = ruleArgument1 as prettier.Options;
         break;
       case 'string': {
-        const filePath = path.resolve(process.cwd(), ruleArgument1 as string);
-        const resolvedConfig = prettier.resolveConfig.sync(filePath);
+        const configFilePath = path.resolve(
+          process.cwd(),
+          ruleArgument1 as string,
+        );
+
+        const resolvedConfig = prettier.resolveConfig.sync(
+          sourceFile.fileName,
+          { config: configFilePath },
+        );
 
         // istanbul ignore next
         if (resolvedConfig === null) {
-          throw new Error(`Config file not found: ${filePath}`);
+          throw new Error(`Config file not found: ${configFilePath}`);
         }
 
         options = resolvedConfig;

tests/prettier/specified-config/tslint.json

@@ -1,6 +1,6 @@
 {
   "rulesDirectory": ["../../../rules"],
   "rules": {
-    "prettier": [true, "./fixtures/no-semi"]
+    "prettier": [true, "./fixtures/no-semi/.prettierrc"]
   }
 }