fix: log full key def (#5)

* fix: log the full key if not found

* fix: update tests

envconfig.go

@@ -194,11 +194,7 @@ func Process(prefix string, spec interface{}) error {
 		req := info.Tags.Get("required")
 		if value == "" {
 			if isTrue(req) {
-				key := info.Key
-				if info.Alt != "" {
-					key = info.Alt
-				}
-				return fmt.Errorf("required key %s missing value", key)
+				return fmt.Errorf("required key %s missing value", info.Key)
 			}
 			continue
 		}

envconfig_test.go

@@ -926,11 +926,47 @@ func TestErrorMessageForRequiredAltVar(t *testing.T) {
 		t.Error("no failure when missing required variable")
 	}
 
+	if !strings.Contains(err.Error(), " ENV_CONFIG_BAR ") {
+		t.Errorf("expected error message to contain ENV_CONFIG_BAR, got \"%v\"", err)
+	}
+}
+
+func TestErrorMessageForRequiredAltVarNoPrefix(t *testing.T) {
+	var s struct {
+		Foo string `envconfig:"BAR" required:"true"`
+	}
+
+	os.Clearenv()
+	err := Process("", &s)
+
+	if err == nil {
+		t.Error("no failure when missing required variable")
+	}
+
 	if !strings.Contains(err.Error(), " BAR ") {
 		t.Errorf("expected error message to contain BAR, got \"%v\"", err)
 	}
 }
 
+func TestErrorMessageForRequiredAltVarNestedStruct(t *testing.T) {
+	var s struct {
+		Foo struct {
+			Bar string `envconfig:"BAR" required:"true"`
+		} `envconfig:"FOO" required:"true"`
+	}
+
+	os.Clearenv()
+	err := Process("ENV_CONFIG", &s)
+
+	if err == nil {
+		t.Error("no failure when missing required variable")
+	}
+
+	if !strings.Contains(err.Error(), " ENV_CONFIG_FOO_BAR ") {
+		t.Errorf("expected error message to contain ENV_CONFIG_FOO_BAR, got \"%v\"", err)
+	}
+}
+
 func TestNonTaggedFields(t *testing.T) {
 	var s struct {
 		Foo string `envconfig:"FOO"`