[BUG] HandlebarsEngineAdapter.java failed to use custom FieldValueResolver causing IllegalAccessException for maps (#19634)

* Update HandlebarsEngineAdapter.java

The old MY_FIELD_VALUE_RESOLVER.INSTANCE is equivalent to FieldValueResolver.INSTANCE, which is assigned `new FieldValueResolver();` so our custom class was never used.

* Add test verifying partial template works; Extract accessAwareFieldValueResolver; Add test verifying priority fo values extracted from object

modules/openapi-generator/src/main/java/org/openapitools/codegen/templating/HandlebarsEngineAdapter.java

@@ -33,6 +33,7 @@ import com.github.jknack.handlebars.io.TemplateSource;
 import lombok.Setter;
 import org.openapitools.codegen.api.AbstractTemplatingEngineAdapter;
 import org.openapitools.codegen.api.TemplatingExecutor;
+import org.openapitools.codegen.templating.handlebars.AccessAwareFieldValueResolver;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -45,7 +46,7 @@ import java.util.Set;
 import java.util.stream.Collectors;
 
 public class HandlebarsEngineAdapter extends AbstractTemplatingEngineAdapter {
-     final Logger LOGGER = LoggerFactory.getLogger(HandlebarsEngineAdapter.class);
+    final Logger LOGGER = LoggerFactory.getLogger(HandlebarsEngineAdapter.class);
     private final String[] extensions = {"handlebars", "hbs"};
 
     // We use this as a simple lookup for valid file name extensions. This adapter will inspect .mustache (built-in) and infer the relevant handlebars filename
@@ -73,36 +74,13 @@ public class HandlebarsEngineAdapter extends AbstractTemplatingEngineAdapter {
             }
         };
 
-        // $ref: https://github.com/jknack/handlebars.java/issues/917
-        var MY_FIELD_VALUE_RESOLVER = new FieldValueResolver() {
-            @Override
-            protected Set<FieldWrapper> members(
-                    Class<?> clazz) {
-                var members = super.members(clazz);
-                return members.stream()
-                    .filter(fw -> isValidField(fw))
-                    .collect(Collectors.toSet());
-            }
-
-            boolean isValidField(
-                    FieldWrapper fw) {
-                if (fw instanceof AccessibleObject) {
-                    if (isUseSetAccessible(fw)) {
-                        return true;
-                    }
-                    return false;
-                }
-                return true;
-            }
-        };
-
         Context context = Context
                 .newBuilder(bundle)
                 .resolver(
                         MapValueResolver.INSTANCE,
                         JavaBeanValueResolver.INSTANCE,
-                        MY_FIELD_VALUE_RESOLVER.INSTANCE,
-                        MethodValueResolver.INSTANCE)
+                        MethodValueResolver.INSTANCE,
+                        AccessAwareFieldValueResolver.INSTANCE)
                 .build();
 
         Handlebars handlebars = new Handlebars(loader);

modules/openapi-generator/src/main/java/org/openapitools/codegen/templating/handlebars/AccessAwareFieldValueResolver.java

@@ -0,0 +1,28 @@
+package org.openapitools.codegen.templating.handlebars;
+
+import com.github.jknack.handlebars.context.FieldValueResolver;
+
+import java.lang.reflect.AccessibleObject;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+// $ref: https://github.com/jknack/handlebars.java/issues/917
+public class AccessAwareFieldValueResolver extends FieldValueResolver {
+
+    public static final AccessAwareFieldValueResolver INSTANCE = new AccessAwareFieldValueResolver();
+
+    @Override
+    protected Set<FieldValueResolver.FieldWrapper> members(Class<?> clazz) {
+        var members = super.members(clazz);
+        return members.stream()
+                .filter(this::isValidField)
+                .collect(Collectors.toSet());
+    }
+
+    boolean isValidField(FieldWrapper fw) {
+        if (fw instanceof AccessibleObject) {
+            return isUseSetAccessible(fw);
+        }
+        return true;
+    }
+}

modules/openapi-generator/src/test/java/org/openapitools/codegen/templating/HandlebarsEngineAdapterTest.java

@@ -1,9 +1,14 @@
 package org.openapitools.codegen.templating;
 
+import org.mockito.Mockito;
+import org.openapitools.codegen.api.TemplatingExecutor;
 import org.testng.annotations.DataProvider;
 import org.testng.annotations.Test;
 
-import static org.testng.Assert.*;
+import java.io.IOException;
+import java.util.Map;
+
+import static org.testng.Assert.assertEquals;
 
 public class HandlebarsEngineAdapterTest {
     @Test(dataProvider = "handlesFileExpectations")
@@ -33,4 +38,73 @@ public class HandlebarsEngineAdapterTest {
                 {"README.md", false, "Should not attempt to handle non-handlebars extensions (other than mustache)"}
         };
     }
+
+    @Test(description = "verify https://github.com/jknack/handlebars.java/issues/940#issue-1111612043 is fixed")
+    public void testHandlePartialTemplate() throws IOException {
+        // Given
+        HandlebarsEngineAdapter adapter = new HandlebarsEngineAdapter();
+        TemplatingExecutor executorMock = Mockito.mock(TemplatingExecutor.class);
+        Mockito.when(executorMock.getFullTemplateContents("outerTemplate.hbs")).thenReturn("Contents: {{>innerTemplate}}");
+        Mockito.when(executorMock.getFullTemplateContents("innerTemplate.hbs")).thenReturn("'Specific contents'");
+
+        // When
+        String generatedFile = adapter.compileTemplate(executorMock, Map.of(), "outerTemplate.hbs");
+
+        // Then
+        assertEquals(generatedFile, "Contents: 'Specific contents'");
+    }
+
+    @Test(description = "should prioritize public getters over breaking encapsulation")
+    public void testResolverPriority() throws IOException {
+        // Given
+        HandlebarsEngineAdapter adapter = new HandlebarsEngineAdapter();
+        TemplatingExecutor executorMock = Mockito.mock(TemplatingExecutor.class);
+        Mockito.when(executorMock.getFullTemplateContents("outerTemplate.hbs")).thenReturn(
+                "Contents: {{#propertyObj}}\n" +
+                        "  public getter: {{valueMethodAndBean}}\n" + 
+                        "  public method: {{valueAndMethod}}\n" + 
+                        "  private property: {{valueOnly}}{{/propertyObj}}");
+
+        Map<String, Object> bundle = Map.of("propertyObj", new PropertyObject());
+
+        // When
+        String generatedFile = adapter.compileTemplate(executorMock, bundle, "outerTemplate.hbs");
+
+        // Then
+        assertEquals(generatedFile, "Contents: \n" +
+                "  public getter: get_raw_data1_formatted\n" +
+                "  public method: raw_data2_formatted\n" +
+                "  private property: raw_data3");
+    }
+
+    static class PropertyObject {
+        /**
+         * getter-exposed
+         */
+        private final String valueMethodAndBean = "raw_data1";
+
+        public String valueMethodAndBean() {
+            return valueMethodAndBean + "_formatted";
+        }
+
+        public String getValueMethodAndBean() {
+            return "get_" + valueMethodAndBean();
+        }
+
+        /**
+         * method-exposed
+         */
+        private final String valueAndMethod = "raw_data2";
+
+        public String valueAndMethod() {
+            return valueAndMethod + "_formatted";
+        }
+
+        /**
+         * private
+         * note: ideally we long-term move towards respecting encapsulation where possible
+         */
+        @SuppressWarnings({"unused", "java:S1068"}) // this private value is still read by our HandleBars engine
+        private final String valueOnly = "raw_data3";
+    }
 }

modules/openapi-generator/src/test/java/org/openapitools/codegen/templating/handlebars/StringHelpersTest.java

@@ -21,7 +21,7 @@ public class StringHelpersTest {
         Context context = Context
                 .newBuilder(data)
                 .resolver(
-                        FieldValueResolver.INSTANCE)
+                        AccessAwareFieldValueResolver.INSTANCE)
                 .build();
 
         Template tmpl = handlebars.compileInline(template);