Repository: spf13/viper (go)

Issue:
Exchangeable Logger
Hi,

I want to use viper with a custom logger. Viper contains currently logs to `log.Fatal`, `log.Printf`, `jww.INFO.Println`, `jww.ERROR.Println`.

Both `log` and `jww` (jwalterweatherman) allow custom output streams but using them gets a bit hacky with my system wide log format, log level and special log files for different components.

If you're interessested I would create a pull request for a more exchangeable logging approach.

That could probably look like this:
``` go
// Logger collects log messages.
var Logger interface {
    Infof(string, ...interface{})
    Errorf(string, ...interface{})
    Fatalf(string, ...interface{})

    Info(...interface{})
    Error(...interface{})
    Fatal(...interface{})
} = logrus.New()

func DoX(){
    logger.Info("Done X")
}
```

Kind Regards

GeneriK

Pull request description:
Add new logger interface
Closes #680 
Closes #682

Patch:
diff --git a/logger.go b/logger.go
new file mode 100644
index 0000000..0115067
--- /dev/null
+++ b/logger.go
@@ -0,0 +1,77 @@
+package viper
+
+import (
+	"fmt"
+
+	jww "github.com/spf13/jwalterweatherman"
+)
+
+// Logger is a unified interface for various logging use cases and practices, including:
+// 		- leveled logging
+// 		- structured logging
+type Logger interface {
+	// Trace logs a Trace event.
+	//
+	// Even more fine-grained information than Debug events.
+	// Loggers not supporting this level should fall back to Debug.
+	Trace(msg string, keyvals ...interface{})
+
+	// Debug logs a Debug event.
+	//
+	// A verbose series of information events.
+	// They are useful when debugging the system.
+	Debug(msg string, keyvals ...interface{})
+
+	// Info logs an Info event.
+	//
+	// General information about what's happening inside the system.
+	Info(msg string, keyvals ...interface{})
+
+	// Warn logs a Warn(ing) event.
+	//
+	// Non-critical events that should be looked at.
+	Warn(msg string, keyvals ...interface{})
+
+	// Error logs an Error event.
+	//
+	// Critical events that require immediate attention.
+	// Loggers commonly provide Fatal and Panic levels above Error level,
+	// but exiting and panicing is out of scope for a logging library.
+	Error(msg string, keyvals ...interface{})
+}
+
+type jwwLogger struct{}
+
+func (jwwLogger) Trace(msg string, keyvals ...interface{}) {
+	jww.TRACE.Printf(jwwLogMessage(msg, keyvals...))
+}
+
+func (jwwLogger) Debug(msg string, keyvals ...interface{}) {
+	jww.DEBUG.Printf(jwwLogMessage(msg, keyvals...))
+}
+
+func (jwwLogger) Info(msg string, keyvals ...interface{}) {
+	jww.INFO.Printf(jwwLogMessage(msg, keyvals...))
+}
+
+func (jwwLogger) Warn(msg string, keyvals ...interface{}) {
+	jww.WARN.Printf(jwwLogMessage(msg, keyvals...))
+}
+
+func (jwwLogger) Error(msg string, keyvals ...interface{}) {
+	jww.ERROR.Printf(jwwLogMessage(msg, keyvals...))
+}
+
+func jwwLogMessage(msg string, keyvals ...interface{}) string {
+	out := msg
+
+	if len(keyvals) > 0 && len(keyvals)%2 == 1 {
+		keyvals = append(keyvals, nil)
+	}
+
+	for i := 0; i <= len(keyvals)-2; i += 2 {
+		out = fmt.Sprintf("%s %v=%v", out, keyvals[i], keyvals[i+1])
+	}
+
+	return out
+}
diff --git a/util.go b/util.go
index 742f997..ee7a86d 100644
--- a/util.go
+++ b/util.go
@@ -19,7 +19,6 @@ import (
 	"unicode"
 
 	"github.com/spf13/cast"
-	jww "github.com/spf13/jwalterweatherman"
 )
 
 // ConfigParseError denotes failing to parse configuration file.
@@ -87,8 +86,8 @@ func insensitiviseMap(m map[string]interface{}) {
 	}
 }
 
-func absPathify(inPath string) string {
-	jww.INFO.Println("Trying to resolve absolute path to", inPath)
+func absPathify(logger Logger, inPath string) string {
+	logger.Info("trying to resolve absolute path", "path", inPath)
 
 	if inPath == "$HOME" || strings.HasPrefix(inPath, "$HOME"+string(os.PathSeparator)) {
 		inPath = userHomeDir() + inPath[5:]
@@ -105,8 +104,8 @@ func absPathify(inPath string) string {
 		return filepath.Clean(p)
 	}
 
-	jww.ERROR.Println("Couldn't discover absolute path")
-	jww.ERROR.Println(err)
+	logger.Error(fmt.Errorf("could not discover absolute path: %w", err).Error())
+
 	return ""
 }
 
diff --git a/viper.go b/viper.go
index 0b27c19..4a99358 100644
--- a/viper.go
+++ b/viper.go
@@ -39,7 +39,6 @@ import (
 	"github.com/mitchellh/mapstructure"
 	"github.com/spf13/afero"
 	"github.com/spf13/cast"
-	jww "github.com/spf13/jwalterweatherman"
 	"github.com/spf13/pflag"
 	"github.com/subosito/gotenv"
 	"gopkg.in/ini.v1"
@@ -260,6 +259,8 @@ type Viper struct {
 	properties *properties.Properties
 
 	onConfigChange func(fsnotify.Event)
+
+	logger Logger
 }
 
 // New returns an initialized Viper instance.
@@ -277,6 +278,7 @@ func New() *Viper {
 	v.env = make(map[string][]string)
 	v.aliases = make(map[string]string)
 	v.typeByDefValue = false
+	v.logger = jwwLogger{}
 
 	return v
 }
@@ -517,8 +519,9 @@ func AddConfigPath(in string) { v.AddConfigPath(in) }
 
 func (v *Viper) AddConfigPath(in string) {
 	if in != "" {
-		absin := absPathify(in)
-		jww.INFO.Println("adding", absin, "to paths to search")
+		absin := absPathify(v.logger, in)
+
+		v.logger.Info("adding path to search paths", "path", absin)
 		if !stringInSlice(absin, v.configPaths) {
 			v.configPaths = append(v.configPaths, absin)
 		}
@@ -542,7 +545,8 @@ func (v *Viper) AddRemoteProvider(provider, endpoint, path string) error {
 		return UnsupportedRemoteProviderError(provider)
 	}
 	if provider != "" && endpoint != "" {
-		jww.INFO.Printf("adding %s:%s to remote provider list", provider, endpoint)
+		v.logger.Info("adding remote provider", "provider", provider, "endpoint", endpoint)
+
 		rp := &defaultRemoteProvider{
 			endpoint: endpoint,
 			provider: provider,
@@ -574,7 +578,8 @@ func (v *Viper) AddSecureRemoteProvider(provider, endpoint, path, secretkeyring
 		return UnsupportedRemoteProviderError(provider)
 	}
 	if provider != "" && endpoint != "" {
-		jww.INFO.Printf("adding %s:%s to remote provider list", provider, endpoint)
+		v.logger.Info("adding remote provider", "provider", provider, "endpoint", endpoint)
+
 		rp := &defaultRemoteProvider{
 			endpoint:      endpoint,
 			provider:      provider,
@@ -1390,14 +1395,15 @@ func (v *Viper) registerAlias(alias string, key string) {
 			v.aliases[alias] = key
 		}
 	} else {
-		jww.WARN.Println("Creating circular reference alias", alias, key, v.realKey(key))
+		v.logger.Warn("creating circular reference alias", "alias", alias, "key", key, "real_key", v.realKey(key))
 	}
 }
 
 func (v *Viper) realKey(key string) string {
 	newkey, exists := v.aliases[key]
 	if exists {
-		jww.DEBUG.Println("Alias", key, "to", newkey)
+		v.logger.Debug("key is an alias", "alias", key, "to", newkey)
+
 		return v.realKey(newkey)
 	}
 	return key
@@ -1458,7 +1464,7 @@ func (v *Viper) Set(key string, value interface{}) {
 func ReadInConfig() error { return v.ReadInConfig() }
 
 func (v *Viper) ReadInConfig() error {
-	jww.INFO.Println("Attempting to read in config file")
+	v.logger.Info("attempting to read in config file")
 	filename, err := v.getConfigFile()
 	if err != nil {
 		return err
@@ -1468,7 +1474,7 @@ func (v *Viper) ReadInConfig() error {
 		return UnsupportedConfigError(v.getConfigType())
 	}
 
-	jww.DEBUG.Println("Reading file: ", filename)
+	v.logger.Debug("reading file", "file", filename)
 	file, err := afero.ReadFile(v.fs, filename)
 	if err != nil {
 		return err
@@ -1489,7 +1495,7 @@ func (v *Viper) ReadInConfig() error {
 func MergeInConfig() error { return v.MergeInConfig() }
 
 func (v *Viper) MergeInConfig() error {
-	jww.INFO.Println("Attempting to merge in config file")
+	v.logger.Info("attempting to merge in config file")
 	filename, err := v.getConfigFile()
 	if err != nil {
 		return err
@@ -1580,7 +1586,8 @@ func (v *Viper) SafeWriteConfigAs(filename string) error {
 }
 
 func (v *Viper) writeConfig(filename string, force bool) error {
-	jww.INFO.Println("Attempting to write configuration to file.")
+	v.logger.Info("attempting to write configuration to file")
+
 	var configType string
 
 	ext := filepath.Ext(filename)
@@ -1796,7 +1803,7 @@ func mergeMaps(
 	for sk, sv := range src {
 		tk := keyExists(sk, tgt)
 		if tk == "" {
-			jww.TRACE.Printf("tk=\"\", tgt[%s]=%v", sk, sv)
+			v.logger.Trace("", "tk", "\"\"", fmt.Sprintf("tgt[%s]", sk), sv)
 			tgt[sk] = sv
 			if itgt != nil {
 				itgt[sk] = sv
@@ -1806,7 +1813,7 @@ func mergeMaps(
 
 		tv, ok := tgt[tk]
 		if !ok {
-			jww.TRACE.Printf("tgt[%s] != ok, tgt[%s]=%v", tk, sk, sv)
+			v.logger.Trace("", fmt.Sprintf("ok[%s]", tk), false, fmt.Sprintf("tgt[%s]", sk), sv)
 			tgt[sk] = sv
 			if itgt != nil {
 				itgt[sk] = sv
@@ -1817,27 +1824,38 @@ func mergeMaps(
 		svType := reflect.TypeOf(sv)
 		tvType := reflect.TypeOf(tv)
 		if tvType != nil && svType != tvType { // Allow for the target to be nil
-			jww.ERROR.Printf(
-				"svType != tvType; key=%s, st=%v, tt=%v, sv=%v, tv=%v",
-				sk, svType, tvType, sv, tv)
+			v.logger.Error(
+				"svType != tvType",
+				"key", sk,
+				"st", svType,
+				"tt", tvType,
+				"sv", sv,
+				"tv", tv,
+			)
 			continue
 		}
 
-		jww.TRACE.Printf("processing key=%s, st=%v, tt=%v, sv=%v, tv=%v",
-			sk, svType, tvType, sv, tv)
+		v.logger.Trace(
+			"processing",
+			"key", sk,
+			"st", svType,
+			"tt", tvType,
+			"sv", sv,
+			"tv", tv,
+		)
 
 		switch ttv := tv.(type) {
 		case map[interface{}]interface{}:
-			jww.TRACE.Printf("merging maps (must convert)")
+			v.logger.Trace("merging maps (must convert)")
 			tsv := sv.(map[interface{}]interface{})
 			ssv := castToMapStringInterface(tsv)
 			stv := castToMapStringInterface(ttv)
 			mergeMaps(ssv, stv, ttv)
 		case map[string]interface{}:
-			jww.TRACE.Printf("merging maps")
+			v.logger.Trace("merging maps")
 			mergeMaps(sv.(map[string]interface{}), ttv, nil)
 		default:
-			jww.TRACE.Printf("setting value")
+			v.logger.Trace("setting value")
 			tgt[tk] = sv
 			if itgt != nil {
 				itgt[tk] = sv
@@ -1872,7 +1890,7 @@ func (v *Viper) getKeyValueConfig() error {
 	for _, rp := range v.remoteProviders {
 		val, err := v.getRemoteConfig(rp)
 		if err != nil {
-			jww.ERROR.Printf("get remote config: %s", err)
+			v.logger.Error(fmt.Errorf("get remote config: %w", err).Error())
 
 			continue
 		}
diff --git a/viper_go1_15.go b/viper_go1_15.go
index a679af5..19a771c 100644
--- a/viper_go1_15.go
+++ b/viper_go1_15.go
@@ -9,13 +9,12 @@ import (
 	"path/filepath"
 
 	"github.com/spf13/afero"
-	jww "github.com/spf13/jwalterweatherman"
 )
 
 // Search all configPaths for any config file.
 // Returns the first path that exists (and is a config file).
 func (v *Viper) findConfigFile() (string, error) {
-	jww.INFO.Println("Searching for config in ", v.configPaths)
+	v.logger.Info("searching for config in paths", "paths", v.configPaths)
 
 	for _, cp := range v.configPaths {
 		file := v.searchInPath(cp)
@@ -27,11 +26,11 @@ func (v *Viper) findConfigFile() (string, error) {
 }
 
 func (v *Viper) searchInPath(in string) (filename string) {
-	jww.DEBUG.Println("Searching for config in ", in)
+	v.logger.Debug("searching for config in path", "path", in)
 	for _, ext := range SupportedExts {
-		jww.DEBUG.Println("Checking for", filepath.Join(in, v.configName+"."+ext))
+		v.logger.Debug("checking if file exists", "file", filepath.Join(in, v.configName+"."+ext))
 		if b, _ := exists(v.fs, filepath.Join(in, v.configName+"."+ext)); b {
-			jww.DEBUG.Println("Found: ", filepath.Join(in, v.configName+"."+ext))
+			v.logger.Debug("found file", "file", filepath.Join(in, v.configName+"."+ext))
 			return filepath.Join(in, v.configName+"."+ext)
 		}
 	}


Test patch:
diff --git a/util_test.go b/util_test.go
index b294b49..cb4e620 100644
--- a/util_test.go
+++ b/util_test.go
@@ -87,7 +87,7 @@ func TestAbsPathify(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		got := absPathify(test.input)
+		got := absPathify(jwwLogger{}, test.input)
 		if got != test.output {
 			t.Errorf("Got %v\nexpected\n%q", got, test.output)
 		}