fix(core): VariableRenderer should expose alternativeRender

core/src/main/java/io/kestra/core/runners/VariableRenderer.java

@@ -99,10 +99,16 @@ public String renderOnce(String inline, Map<String, Object> variables) throws Il
             Writer writer = new JsonWriter(new StringWriter());
             compiledTemplate.evaluate(writer, variables);
             result = writer.toString();
-        } catch (IOException e) {
-            throw new IllegalVariableEvaluationException(e);
-        } catch (PebbleException e) {
-            throw properPebbleException(e);
+        } catch (IOException | PebbleException e) {
+            String alternativeRender = this.alternativeRender(e, inline, variables);
+            if (alternativeRender == null) {
+                if (e instanceof PebbleException) {
+                    throw properPebbleException((PebbleException) e);
+                }
+                throw new IllegalVariableEvaluationException(e);
+            } else {
+                result = alternativeRender;
+            }
         }
 
         // post-process raw tags
@@ -111,6 +117,18 @@ public String renderOnce(String inline, Map<String, Object> variables) throws Il
         return result;
     }
 
+    /**
+     * This method can be used in fallback for rendering an input string.
+     *
+     * @param e         The exception that was throw by the default variable renderer.
+     * @param inline    The expression to be rendered.
+     * @param variables The context variables.
+     * @return          The rendered string.
+     */
+    protected String alternativeRender(Exception e, String inline, Map<String, Object> variables) throws IllegalVariableEvaluationException {
+        return null;
+    }
+
     private static String putBackRawTags(Map<String, String> replacers, String result) {
         for (var entry : replacers.entrySet()) {
             result = result.replace(entry.getKey(), entry.getValue());

core/src/test/java/io/kestra/core/runners/VariableRendererTest.java

@@ -0,0 +1,43 @@
+package io.kestra.core.runners;
+
+import io.kestra.core.exceptions.IllegalVariableEvaluationException;
+import io.micronaut.context.ApplicationContext;
+import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
+import jakarta.inject.Inject;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Map;
+
+@MicronautTest
+class VariableRendererTest {
+
+    @Inject
+    ApplicationContext applicationContext;
+
+    @Inject
+    VariableRenderer.VariableConfiguration variableConfiguration;
+
+    @Test
+    void shouldRenderUsingAlternativeRendering() throws IllegalVariableEvaluationException {
+        TestVariableRenderer renderer = new TestVariableRenderer(applicationContext, variableConfiguration);
+        String render = renderer.render("{{ dummy }}", Map.of());
+        Assertions.assertEquals("result", render);
+    }
+
+
+    public static class TestVariableRenderer extends VariableRenderer {
+
+        public TestVariableRenderer(ApplicationContext applicationContext,
+                                    VariableConfiguration variableConfiguration) {
+            super(applicationContext, variableConfiguration);
+        }
+
+        @Override
+        protected String alternativeRender(Exception e, String inline, Map<String, Object> variables) throws IllegalVariableEvaluationException {
+            return "result";
+        }
+    }
+
+
+}