From 3adf8b452028059d3612fe697378ce4af0c94449 Mon Sep 17 00:00:00 2001
From: andig <andi@evcc.io>
Date: Mon, 22 Dec 2025 13:55:52 +0100
Subject: [PATCH] Templates: error on missing required values (#25932)

---
 tests/vehicle-error.evcc.yaml   |  1 +
 util/templates/template.go      |  8 ++++++++
 util/templates/template_test.go | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/tests/vehicle-error.evcc.yaml b/tests/vehicle-error.evcc.yaml
index bcce474b8..d1f06a05f 100755
--- a/tests/vehicle-error.evcc.yaml
+++ b/tests/vehicle-error.evcc.yaml
@@ -50,5 +50,6 @@ vehicles:
     type: template
     template: tesla # not optimal, since real communication with tesla server is happening
     title: Broken Tesla
+    clientId: test_client_id
     accessToken: A
     refreshToken: B
diff --git a/util/templates/template.go b/util/templates/template.go
index 10464e44e..bd0f37ee9 100644
--- a/util/templates/template.go
+++ b/util/templates/template.go
@@ -7,6 +7,7 @@ import (
 	"slices"
 	"strconv"
 	"strings"
+	"testing"
 	"text/template"
 
 	"github.com/Masterminds/sprig/v3"
@@ -354,6 +355,13 @@ func (t *Template) RenderResult(renderMode int, other map[string]any) ([]byte, m
 				if val != nil {
 					s = p.yamlQuote(fmt.Sprintf("%v", val))
 				}
+
+				// validate required fields from yaml
+				if s == "" && p.IsRequired() && (renderMode == RenderModeUnitTest ||
+					renderMode == RenderModeInstance && !testing.Testing()) {
+					return nil, nil, fmt.Errorf("missing required `%s`", p.Name)
+				}
+
 				res[out] = s
 			}
 		}
diff --git a/util/templates/template_test.go b/util/templates/template_test.go
index 9432523d0..b54e33573 100644
--- a/util/templates/template_test.go
+++ b/util/templates/template_test.go
@@ -32,3 +32,36 @@ func TestPresets(t *testing.T) {
 		{Name: "last"},
 	}, tmpl.Params)
 }
+
+func TestRequired(t *testing.T) {
+	tmpl := &Template{
+		TemplateDefinition: TemplateDefinition{
+			Params: []Param{
+				{
+					Name:     "param",
+					Required: true,
+				},
+			},
+		},
+	}
+
+	_, _, err := tmpl.RenderResult(RenderModeUnitTest, map[string]any{
+		"Param": "foo",
+	})
+	require.NoError(t, err)
+
+	_, _, err = tmpl.RenderResult(RenderModeUnitTest, map[string]any{
+		"Param": "",
+	})
+	require.Error(t, err)
+
+	_, _, err = tmpl.RenderResult(RenderModeUnitTest, map[string]any{
+		"Param": nil,
+	})
+	require.Error(t, err)
+
+	_, _, err = tmpl.RenderResult(RenderModeDocs, map[string]any{
+		"Param": nil,
+	})
+	require.NoError(t, err)
+}