From 42a499d7ac2c02fe711ff1d29d45aa57cbff8edb Mon Sep 17 00:00:00 2001
From: Albert Vaca <albertvaka@gmail.com>
Date: Tue, 26 Mar 2019 15:14:00 +0100
Subject: [PATCH] Warn when a yaml file has duplicated keys

Try using `UnmarshalStrict`, if it fails, print the errors as a warning and try again with plain `Unmarshal`.

Errors look this way:
```
2019/03/26 15:11:33 warning reading config file: yaml: unmarshal errors:
  line 6: key "api_key" already set in map
```
---
 viper.go | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/viper.go b/viper.go
index c8044e1..b098dc8 100644
--- a/viper.go
+++ b/viper.go
@@ -1462,8 +1462,12 @@ func (v *Viper) unmarshalReader(in io.Reader, c map[string]interface{}) error {
 
 	switch strings.ToLower(v.getConfigType()) {
 	case "yaml", "yml":
-		if err := yaml.Unmarshal(buf.Bytes(), &c); err != nil {
-			return ConfigParseError{err}
+		// Try UnmarshalStrict first, so we can warn about duplicated keys
+		if strictErr := yaml.UnmarshalStrict(buf.Bytes(), &c); strictErr != nil {
+			if err := yaml.Unmarshal(buf.Bytes(), &c); err != nil {
+				return ConfigParseError{err}
+			}
+			log.Printf("warning reading config file: %v\n", strictErr)
 		}
 
 	case "json":