Qute: fix handling of missing properties in strict mode

- fixes quarkusio#44674

independent-projects/qute/core/src/main/java/io/quarkus/qute/CompletedStage.java

@@ -61,7 +61,7 @@ public boolean isFailure() {
 
     public T get() {
         if (exception != null) {
-            // Throw an exception if completed exceptionally
+            // Always wrap the original exception if completed exceptionally
             throw new TemplateException(exception);
         }
         return result;
@@ -285,8 +285,12 @@ public CompletionStage<T> whenComplete(BiConsumer<? super T, ? super Throwable>
             Objects.requireNonNull(action).accept(result, exception);
         } catch (Throwable e) {
             if (exception == null) {
+                // "if this stage completed normally but the supplied action throws an exception,
+                // then the returned stage completes exceptionally with the supplied action's exception"
                 return new CompletedStage<>(null, e);
             }
+            // if this stage completed exceptionally and the supplied action throws an exception,
+            // then the returned stage completes exceptionally with this stage's exception
         }
         return this;
     }

independent-projects/qute/core/src/main/java/io/quarkus/qute/EvaluatorImpl.java

@@ -109,7 +109,7 @@ private CompletionStage<Object> resolveNamespace(EvalContext context, Resolution
                         // Continue to the next part of the expression
                         return resolveReference(false, r, parts, resolutionContext, expression, 1);
                     } else if (strictRendering) {
-                        throw propertyNotFound(r, expression);
+                        return CompletedStage.failure(propertyNotFound(r, expression));
                     }
                     return Results.notFound(context);
                 }
@@ -199,9 +199,9 @@ private CompletionStage<Object> resolve(EvalContextImpl evalContext, Iterator<Va
                     notFound = Results.NotFound.from(evalContext);
                 }
             }
-            // If in strict mode then just throw an exception
+            // If in strict mode then just fail
             if (strictRendering && isLastPart) {
-                throw propertyNotFound(notFound, expression);
+                return CompletedStage.failure(propertyNotFound(notFound, expression));
             }
             return CompletedStage.of(notFound);
         }

independent-projects/qute/core/src/test/java/io/quarkus/qute/LetTimeoutTest.java

@@ -0,0 +1,79 @@
+package io.quarkus.qute;
+
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests based on the description from
+ * <a href="https://github.com/quarkusio/quarkus/issues/44674">https://github.com/quarkusio/quarkus/issues/44674</a>.
+ */
+public class LetTimeoutTest {
+
+    Engine engine = Engine.builder().addDefaults().build();
+
+    private static final Map<String, Object> DATA = Map.of(
+            "a", Map.of("b", Map.of()));
+
+    @Test
+    void withDataFactoryMethod() {
+        TemplateInstance instance = engine.parse("""
+                {#let b = a.b}
+                    {c}
+                {/let}
+                """).data(DATA);
+
+        assertThatThrownBy(instance::render)
+                .isInstanceOf(TemplateException.class)
+                .hasRootCauseMessage("Rendering error: Key \"c\" not found in the map with keys [a] in expression {c}");
+    }
+
+    @Test
+    void withInstanceThenDataForEachEntry() {
+        TemplateInstance instance = engine.parse("""
+                {#let b=a.b}
+                    {c}
+                {/let}
+                """).instance();
+        for (var e : DATA.entrySet()) {
+            instance.data(e.getKey(), e.getValue());
+        }
+        assertThatThrownBy(instance::render)
+                .isInstanceOf(TemplateException.class)
+                .hasRootCauseMessage(
+                        "Rendering error: Key \"c\" not found in the template data map with keys [a] in expression {c}");
+    }
+
+    @Test
+    void withSet_withInstanceThenDataForEachEntry() {
+        TemplateInstance instance = engine.parse("""
+                {#set b = a.b}
+                    {c}
+                {/set}
+                """).instance();
+        for (var e : DATA.entrySet()) {
+            instance.data(e.getKey(), e.getValue());
+        }
+        assertThatThrownBy(instance::render)
+                .isInstanceOf(TemplateException.class)
+                .hasRootCauseMessage(
+                        "Rendering error: Key \"c\" not found in the template data map with keys [a] in expression {c}");
+    }
+
+    @Test
+    void withLetWithoutEndTagwithInstanceThenDataForEachEntry() {
+        TemplateInstance instance = engine.parse("""
+                {#let b = a.b}
+                    {c}
+                """).instance();
+        for (var e : DATA.entrySet()) {
+            instance.data(e.getKey(), e.getValue());
+        }
+        assertThatThrownBy(instance::render)
+                .isInstanceOf(TemplateException.class)
+                .hasRootCauseMessage(
+                        "Rendering error: Key \"c\" not found in the template data map with keys [a] in expression {c}");
+    }
+}