config: return error when toml.DecodeFile failed. (#51828) (#52577)

close #51399

config/BUILD.bazel

@@ -37,7 +37,7 @@ go_test(
     data = glob(["**"]),
     embed = [":config"],
     flaky = True,
-    shard_count = 23,
+    shard_count = 24,
     deps = [
         "//testkit/testsetup",
         "//util/logutil",

config/config.go

@@ -1237,13 +1237,16 @@ func (c *Config) RemovedVariableCheck(confFile string) error {
 // Load loads config options from a toml file.
 func (c *Config) Load(confFile string) error {
 	metaData, err := toml.DecodeFile(confFile, c)
+	if err != nil {
+		return err
+	}
 	if c.TokenLimit == 0 {
 		c.TokenLimit = 1000
 	}
 	// If any items in confFile file are not mapped into the Config struct, issue
 	// an error and stop the server from starting.
 	undecoded := metaData.Undecoded()
-	if len(undecoded) > 0 && err == nil {
+	if len(undecoded) > 0 {
 		var undecodedItems []string
 		for _, item := range undecoded {
 			undecodedItems = append(undecodedItems, item.String())

config/config_test.go

@@ -1329,3 +1329,25 @@ func TestAutoScalerConfig(t *testing.T) {
 		conf.UseAutoScaler = false
 	})
 }
+
+func TestInvalidConfigWithDeprecatedConfig(t *testing.T) {
+	tmpDir := t.TempDir()
+	configFile := filepath.Join(tmpDir, "config.toml")
+
+	f, err := os.Create(configFile)
+	require.NoError(t, err)
+
+	_, err = f.WriteString(`
+[log]
+slow-threshold = 1000
+[performance]
+enforce-mpp = 1
+	`)
+	require.NoError(t, err)
+	require.NoError(t, f.Sync())
+
+	var conf Config
+	err = conf.Load(configFile)
+	require.Error(t, err)
+	require.Equal(t, err.Error(), "toml: line 5 (last key \"performance.enforce-mpp\"): incompatible types: TOML value has type int64; destination has type boolean")
+}