Enforce source name uniqueness in config

config.go

@@ -96,13 +96,20 @@ func (c *Config) parse() (*runtimeAssets, error) {
 
 	// Validate the sources (Parse is called later at runtime).
 	// Sources that fail the check are removed from the
-	// SourceSpecs array.
+	// SourceSpecs array. We also check that sources have unique
+	// names.
+	tmp := make(map[string]struct{}{})
 	var srcs []*SourceSpec
 	for _, spec := range c.SourceSpecs {
 		if err := spec.Check(handlerMap); err != nil {
 			merr.Add(fmt.Errorf("source %s: %v", spec.Name, err))
 			continue
 		}
+		if _, ok := tmp[spec.Name]; ok {
+			merr.Add(fmt.Errorf("duplicated source %s", spec.Name))
+			continue
+		}
+		tmp[spec.Name] = struct{}{}
 		srcs = append(srcs, spec)
 	}
 	c.SourceSpecs = srcs