importas: detect duplicate alias or package in the configuration (gol…

…angci#3753)

pkg/golinters/importas.go

@@ -36,12 +36,26 @@ func NewImportAs(settings *config.ImportAsSettings) *goanalysis.Linter {
 			lintCtx.Log.Errorf("failed to parse configuration: %v", err)
 		}
 
+		uniqPackages := make(map[string]config.ImportAsAlias)
+		uniqAliases := make(map[string]config.ImportAsAlias)
 		for _, a := range settings.Alias {
 			if a.Pkg == "" {
 				lintCtx.Log.Errorf("invalid configuration, empty package: pkg=%s alias=%s", a.Pkg, a.Alias)
 				continue
 			}
 
+			if v, ok := uniqPackages[a.Pkg]; ok {
+				lintCtx.Log.Errorf("invalid configuration, multiple aliases for the same package: pkg=%s aliases=[%s,%s]", a.Pkg, a.Alias, v.Alias)
+			} else {
+				uniqPackages[a.Pkg] = a
+			}
+
+			if v, ok := uniqAliases[a.Alias]; ok {
+				lintCtx.Log.Errorf("invalid configuration, multiple packages with the same alias: pkg=%s packages=[%s,%s]", a.Alias, a.Pkg, v.Pkg)
+			} else {
+				uniqAliases[a.Alias] = a
+			}
+
 			err := analyzer.Flags.Set("alias", fmt.Sprintf("%s:%s", a.Pkg, a.Alias))
 			if err != nil {
 				lintCtx.Log.Errorf("failed to parse configuration: %v", err)