MM-6839: search relative to executable (#8853)

* MM-6839: searching for paths relative to executable

In addition to searching relative to the current working directory, also
search relative to the location of the binary. This helps locate config
and i18n files when invoking an absolute path to the mattermost binary.

* MM-6839: find mattermost/ binary using utils.FindFile

utils/config_test.go

@@ -46,20 +46,172 @@ func TestTimezoneConfig(t *testing.T) {
 }
 
 func TestFindConfigFile(t *testing.T) {
-	dir, err := ioutil.TempDir("", "")
-	require.NoError(t, err)
-	defer os.RemoveAll(dir)
+	t.Run("config.json in current working directory, not inside config/", func(t *testing.T) {
+		// Force a unique working directory
+		cwd, err := ioutil.TempDir("", "")
+		require.NoError(t, err)
+		defer os.RemoveAll(cwd)
 
-	path := filepath.Join(dir, "config.json")
-	require.NoError(t, ioutil.WriteFile(path, []byte("{}"), 0600))
+		prevDir, err := os.Getwd()
+		require.NoError(t, err)
+		defer os.Chdir(prevDir)
+		os.Chdir(cwd)
 
-	assert.Equal(t, path, FindConfigFile(path))
+		configJson, err := filepath.Abs("config.json")
+		require.NoError(t, err)
+		require.NoError(t, ioutil.WriteFile(configJson, []byte("{}"), 0600))
 
-	prevDir, err := os.Getwd()
-	require.NoError(t, err)
-	defer os.Chdir(prevDir)
-	os.Chdir(dir)
-	assert.Equal(t, path, FindConfigFile(path))
+		// Relative paths end up getting symlinks fully resolved.
+		configJsonResolved, err := filepath.EvalSymlinks(configJson)
+		require.NoError(t, err)
+
+		assert.Equal(t, configJsonResolved, FindConfigFile("config.json"))
+	})
+
+	t.Run("config/config.json from various paths", func(t *testing.T) {
+		// Create the following directory structure:
+		// tmpDir1/
+		//   config/
+		//     config.json
+		//   tmpDir2/
+		//     tmpDir3/
+		//       tmpDir4/
+		//         tmpDir5/
+		tmpDir1, err := ioutil.TempDir("", "")
+		require.NoError(t, err)
+		defer os.RemoveAll(tmpDir1)
+
+		err = os.Mkdir(filepath.Join(tmpDir1, "config"), 0700)
+		require.NoError(t, err)
+
+		tmpDir2, err := ioutil.TempDir(tmpDir1, "")
+		require.NoError(t, err)
+
+		tmpDir3, err := ioutil.TempDir(tmpDir2, "")
+		require.NoError(t, err)
+
+		tmpDir4, err := ioutil.TempDir(tmpDir3, "")
+		require.NoError(t, err)
+
+		tmpDir5, err := ioutil.TempDir(tmpDir4, "")
+		require.NoError(t, err)
+
+		configJson := filepath.Join(tmpDir1, "config", "config.json")
+		require.NoError(t, ioutil.WriteFile(configJson, []byte("{}"), 0600))
+
+		// Relative paths end up getting symlinks fully resolved, so use this below as necessary.
+		configJsonResolved, err := filepath.EvalSymlinks(configJson)
+		require.NoError(t, err)
+
+		testCases := []struct {
+			Description string
+			Cwd         *string
+			FileName    string
+			Expected    string
+		}{
+			{
+				"absolute path to config.json",
+				nil,
+				configJson,
+				configJson,
+			},
+			{
+				"absolute path to config.json from directory containing config.json",
+				&tmpDir1,
+				configJson,
+				configJson,
+			},
+			{
+				"relative path to config.json from directory containing config.json",
+				&tmpDir1,
+				"config.json",
+				configJsonResolved,
+			},
+			{
+				"subdirectory of directory containing config.json",
+				&tmpDir2,
+				"config.json",
+				configJsonResolved,
+			},
+			{
+				"twice-nested subdirectory of directory containing config.json",
+				&tmpDir3,
+				"config.json",
+				configJsonResolved,
+			},
+			{
+				"thrice-nested subdirectory of directory containing config.json",
+				&tmpDir4,
+				"config.json",
+				configJsonResolved,
+			},
+			{
+				"can't find from four nesting levels deep",
+				&tmpDir5,
+				"config.json",
+				"",
+			},
+		}
+
+		for _, testCase := range testCases {
+			t.Run(testCase.Description, func(t *testing.T) {
+				if testCase.Cwd != nil {
+					prevDir, err := os.Getwd()
+					require.NoError(t, err)
+					defer os.Chdir(prevDir)
+					os.Chdir(*testCase.Cwd)
+				}
+
+				assert.Equal(t, testCase.Expected, FindConfigFile(testCase.FileName))
+			})
+		}
+	})
+
+	t.Run("config/config.json relative to executable", func(t *testing.T) {
+		osExecutable, err := os.Executable()
+		require.NoError(t, err)
+		osExecutableDir := filepath.Dir(osExecutable)
+
+		// Force a working directory different than the executable.
+		cwd, err := ioutil.TempDir("", "")
+		require.NoError(t, err)
+		defer os.RemoveAll(cwd)
+
+		prevDir, err := os.Getwd()
+		require.NoError(t, err)
+		defer os.Chdir(prevDir)
+		os.Chdir(cwd)
+
+		testCases := []struct {
+			Description  string
+			RelativePath string
+		}{
+			{
+				"config/config.json",
+				".",
+			},
+			{
+				"../config/config.json",
+				"../",
+			},
+		}
+
+		for _, testCase := range testCases {
+			t.Run(testCase.Description, func(t *testing.T) {
+				// Install the config in config/config.json relative to the executable
+				configJson := filepath.Join(osExecutableDir, testCase.RelativePath, "config", "config.json")
+				require.NoError(t, os.Mkdir(filepath.Dir(configJson), 0700))
+				require.NoError(t, ioutil.WriteFile(configJson, []byte("{}"), 0600))
+				defer os.RemoveAll(filepath.Dir(configJson))
+
+				// Relative paths end up getting symlinks fully resolved.
+				configJsonResolved, err := filepath.EvalSymlinks(configJson)
+				require.NoError(t, err)
+
+				assert.Equal(t, configJsonResolved, FindConfigFile("config.json"))
+			})
+		}
+	})
 }
 
 func TestConfigFromEnviroVars(t *testing.T) {