Extensionless files only allowed when config type is set (#827)

* Only consider files without extension if the config type is explicitly specified

* Hides unused variable in test

* First check for config type then for file without extension

README.md

@@ -101,6 +101,7 @@ where a configuration file is expected.
 
 ```go
 viper.SetConfigName("config") // name of config file (without extension)
+viper.SetConfigType("yaml") // REQUIRED if the config file does not have the extension in the name
 viper.AddConfigPath("/etc/appname/")   // path to look for the config file in
 viper.AddConfigPath("$HOME/.appname")  // call multiple times to add many search paths
 viper.AddConfigPath(".")               // optionally look for config in the working directory
@@ -124,7 +125,7 @@ if err := viper.ReadInConfig(); err != nil {
 // Config file found and successfully parsed
 ```
 
-*NOTE:* You can also have a file without an extension and specify the format programmaticaly. For those configuration files that lie in the home of the user without any extension like `.bashrc`
+*NOTE [since 1.6]:* You can also have a file without an extension and specify the format programmaticaly. For those configuration files that lie in the home of the user without any extension like `.bashrc`
 
 ### Writing Config Files
 

viper.go

@@ -1976,8 +1976,10 @@ func (v *Viper) searchInPath(in string) (filename string) {
 		}
 	}
 
-	if b, _ := exists(v.fs, filepath.Join(in, v.configName)); b {
+	if v.configType != "" {
-		return filepath.Join(in, v.configName)
+		if b, _ := exists(v.fs, filepath.Join(in, v.configName)); b {
+			return filepath.Join(in, v.configName)
+		}
 	}
 
 	return ""

viper_test.go

@@ -307,11 +307,29 @@ func TestBasics(t *testing.T) {
 	assert.NoError(t, err)
 }
 
+func TestSearchInPath_WithoutConfigTypeSet(t *testing.T) {
+	filename := ".dotfilenoext"
+	path := "/tmp"
+	file := filepath.Join(path, filename)
+	SetConfigName(filename)
+	AddConfigPath(path)
+	_, createErr := v.fs.Create(file)
+	defer func() {
+		_ = v.fs.Remove(file)
+	}()
+	assert.NoError(t, createErr)
+	_, err := v.getConfigFile()
+	// unless config type is set, files without extension
+	// are not considered
+	assert.Error(t, err)
+}
+
 func TestSearchInPath(t *testing.T) {
 	filename := ".dotfilenoext"
 	path := "/tmp"
 	file := filepath.Join(path, filename)
 	SetConfigName(filename)
+	SetConfigType("yaml")
 	AddConfigPath(path)
 	_, createErr := v.fs.Create(file)
 	defer func() {