Fix findup when file found in subdirectory

src/configuration.ts

@@ -148,7 +148,7 @@ function findup(filename: string, directory: string): string | undefined {
     while (true) { // tslint:disable-line strict-boolean-expressions
         const res = findFile(directory);
         if (res !== undefined) {
-            return res;
+            return path.join(directory, res);
         }
 
         const parent = path.dirname(directory);

test/configurationTests.ts

@@ -21,6 +21,7 @@ import * as path from "path";
 import {
     convertRuleOptions,
     extendConfigurationFile,
+    findConfigurationPath,
     IConfigurationFile,
     loadConfigurationFromPath,
     parseConfigFile,
@@ -194,6 +195,23 @@ describe("Configuration", () => {
         });
     });
 
+    describe("findConfigurationPath", () => {
+        it("finds the closest tslint.json", () => {
+            assert.strictEqual(
+                findConfigurationPath(null, "./test/files/config-findup/contains-config"),
+                path.resolve("test/files/config-findup/contains-config/tslint.json"),
+            );
+            assert.strictEqual(
+                findConfigurationPath(null, "./test/files/config-findup/no-config"),
+                path.resolve("./test/files/config-findup/tslint.json"),
+            );
+            assert.strictEqual(
+                findConfigurationPath(null, "./test/files/config-findup"),
+                path.resolve("./test/files/config-findup/tslint.json"),
+            );
+        });
+    });
+
     describe("loadConfigurationFromPath", () => {
         it("extends with relative path", () => {
             const config = loadConfigurationFromPath("./test/config/tslint-extends-relative.json");

test/files/config-findup/contains-config/tslint.json

@@ -0,0 +1 @@
+{}

test/files/config-findup/tslint.json

@@ -0,0 +1 @@
+{}