Shouldn't be illegal to access field 'coder'

[agilob]

Hi

I'm updating openapi-generator to jdk11+. I updated handlebars from 4.2.1 to 4.3.0 and started getting this exception in jdk11 and 17

Caused by: com.github.jknack.handlebars.HandlebarsException: testdata-localhost.hbs:1:46: java.lang.IllegalStateException: Shouldn't be illegal to access field 'coder'
    testdata-localhost.hbs:1:46
	at com.github.jknack.handlebars.context.FieldValueResolver.invokeMember(FieldValueResolver.java:217)
	at com.github.jknack.handlebars.context.FieldValueResolver.invokeMember(FieldValueResolver.java:39)
	at com.github.jknack.handlebars.context.MemberValueResolver.resolve(MemberValueResolver.java:59)
	at com.github.jknack.handlebars.context.MemberValueResolver.propertySet(MemberValueResolver.java:194)
	at com.github.jknack.handlebars.Context$CompositeValueResolver.propertySet(Context.java:226)
	at com.github.jknack.handlebars.Context.propertySet(Context.java:569)
	at com.github.jknack.handlebars.Options.propertySet(Options.java:787)
	at com.github.jknack.handlebars.helper.EachHelper.apply(EachHelper.java:84)
	at com.github.jknack.handlebars.internal.Block.merge(Block.java:211)
	at com.github.jknack.handlebars.internal.BaseTemplate.apply(BaseTemplate.java:126)
	at com.github.jknack.handlebars.internal.TemplateList.merge(TemplateList.java:95)
	at com.github.jknack.handlebars.internal.BaseTemplate.apply(BaseTemplate.java:126)
	at com.github.jknack.handlebars.internal.BaseTemplate.apply(BaseTemplate.java:114)
	at com.github.jknack.handlebars.Options.apply(Options.java:538)
	at com.github.jknack.handlebars.helper.EachHelper.apply(EachHelper.java:99)
	at com.github.jknack.handlebars.internal.Block.merge(Block.java:211)
	at com.github.jknack.handlebars.internal.BaseTemplate.apply(BaseTemplate.java:126)
	at com.github.jknack.handlebars.internal.TemplateList.merge(TemplateList.java:95)
	at com.github.jknack.handlebars.internal.BaseTemplate.apply(BaseTemplate.java:126)
	at com.github.jknack.handlebars.internal.BaseTemplate.apply(BaseTemplate.java:114)
	at com.github.jknack.handlebars.internal.ForwardingTemplate.apply(ForwardingTemplate.java:100)
	at org.openapitools.codegen.templating.HandlebarsEngineAdapter.compileTemplate(HandlebarsEngineAdapter.java:92)
	at org.openapitools.codegen.TemplateManager.write(TemplateManager.java:163)
	at org.openapitools.codegen.DefaultGenerator.processTemplateToFile(DefaultGenerator.java:1042)
	at org.openapitools.codegen.DefaultGenerator.generateApis(DefaultGenerator.java:638)
	... 29 more
Caused by: java.lang.IllegalStateException: Shouldn't be illegal to access field 'coder'
	... 54 more
Caused by: java.lang.IllegalAccessException: class com.github.jknack.handlebars.context.FieldValueResolver$FieldMember cannot access a member of class java.lang.String (in module java.base) with modifiers "private final"
	at java.base/jdk.internal.reflect.Reflection.newIllegalAccessException(Reflection.java:361)
	at java.base/java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:591)
	at java.base/java.lang.reflect.Field.checkAccess(Field.java:1075)
	at java.base/java.lang.reflect.Field.get(Field.java:416)
	at com.github.jknack.handlebars.context.FieldValueResolver$FieldMember.get(FieldValueResolver.java:135)
	at com.github.jknack.handlebars.context.FieldValueResolver.invokeMember(FieldValueResolver.java:214)
	... 53 more

This is when running DefaultGeneratorTest.supportCustomTemplateEngine

[agentgt]

See #940

In this class: https://github.com/OpenAPITools/openapi-generator/blob/4d947a1c4579a73c7350ea55153d33ef76ba5d89/modules/openapi-generator/src/main/java/org/openapitools/codegen/templating/HandlebarsEngineAdapter.java

Change the FieldValueResolver to something like:

        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;
            }
        };

However the above has serious backward compatibility issues if you rely on public fields in the JDK which there should not be many other than array lengths.

[agilob]

Integrated in https://github.com/OpenAPITools/openapi-generator/pull/15553