BindingToUnqualifiedCommonType
This code declares a binding for a common value type without a Qualifier annotation.

Category
Severity
WARNING
Maturity

The problem

Guice bindings are keyed by a pair of (optional Annotation, Type).

In most cirumstances, one doesn’t need the annotation, as there’s really just one active implementation:

bind(CoffeeMaker.class).to(RealCoffeeMaker.class);
...
@Inject Office(CoffeeMaker coffeeMaker) {}

However, in other circumstances, you want to bind a simple value (an integer, String, double, etc.). You should use a Qualifier annotation to allow you to get the right Integer back:

bindConstant().annotatedWith(HttpPort.class).to(80);
...
@Inject MyWebServer(@HttpPort Integer httpPort) {}

NOTE: Make sure that your annotation has the @Qualifier meta-annotation on it, otherwise injection systems can’t see them. Guice users can optionally use @BindingAnnotation, but Guice also understands @Qualifier.

This works great, but if your integer binding doesn’t include a Qualifier, it just means that you can ask Guice for “the Integer”, and it will give you a value back:

bind(Integer.class).toInstance(80);
...
@Inject MyWebServer(Integer httpsPort) {}

To avoid confusion in these circumstances, please use a Qualifier annotation when binding simple value types.

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("BindingToUnqualifiedCommonType") to the enclosing element.


Positive examples

BindingToUnqualifiedCommonTypePositiveCases.java

/*
* Copyright 2016 Google Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/


package com.google.errorprone.bugpatterns.inject.guice.testdata;

import com.google.inject.AbstractModule;
import com.google.inject.Provides;

/** Tests for {@code BindingToUnqualifiedCommonType} */
public class BindingToUnqualifiedCommonTypePositiveCases {

/** Regular module */
class Module1 extends AbstractModule {
@Override
protected void configure() {
// BUG: Diagnostic contains: BindingToUnqualifiedCommonType
bind(Integer.class).toInstance(2);

// BUG: Diagnostic contains: BindingToUnqualifiedCommonType
bind(String.class).toInstance("Hello");

// BUG: Diagnostic contains: BindingToUnqualifiedCommonType
bind(Double.class).toProvider(() -> 42.0);

// BUG: Diagnostic contains: BindingToUnqualifiedCommonType
binder().bind(Long.class).toInstance(42L);
}

@Provides
// BUG: Diagnostic contains: BindingToUnqualifiedCommonType
int providesFoo() {
return 42;
}

@Provides
// BUG: Diagnostic contains: BindingToUnqualifiedCommonType
Integer provideBoxedFoo() {
return 42;
}

@Provides
// BUG: Diagnostic contains: BindingToUnqualifiedCommonType
String providesGreeting() {
return "hi";
}
}
}

Negative examples

BindingToUnqualifiedCommonTypeNegativeCases.java

/*
* Copyright 2016 Google Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/


package com.google.errorprone.bugpatterns.inject.guice.testdata;

import com.google.common.collect.ImmutableList;
import com.google.inject.AbstractModule;
import com.google.inject.Binder;
import com.google.inject.BindingAnnotation;
import com.google.inject.Module;
import com.google.inject.Provides;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.List;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/** Tests for {@code BindingToUnqualifiedCommonType} */
public class BindingToUnqualifiedCommonTypeNegativeCases {

// All of the tagged instances would normally be flagged, but aren't because it's in a JUnit4
// class
@RunWith(JUnit4.class)
static class MyTestClass {
/** Regular module */
class Module1 extends AbstractModule {
@Override
protected void configure() {
bind(Integer.class).toInstance(2);
bind(String.class).toInstance("Hello");
bind(Double.class).toProvider(() -> 42.0);
binder().bind(Long.class).toInstance(42L);
}

@Provides
int providesFoo() {
return 42;
}

@Provides
Integer provideBoxedFoo() {
return 42;
}

@Provides
String providesGreeting() {
return "hi";
}
}
}

/** Regular module */
class Module1 extends AbstractModule {
@Override
protected void configure() {
// Bindings to unannotated complex instances
bind(A.class).toInstance(new A());

// Binding to literals, but with a binding annotation
bind(Integer.class).annotatedWith(MyBindingAnnotation.class).toInstance(42);
}

@Provides
List<Integer> providesFoo() {
return ImmutableList.of(42);
}
}

/** implements the Module interface directly */
class Module2 implements Module {
@Override
public void configure(Binder binder) {}

@Provides
@MyBindingAnnotation
int providesFoo() {
return 42;
}
}

class A {}

@BindingAnnotation
@Retention(RetentionPolicy.RUNTIME)
@interface MyBindingAnnotation {}
}