Summary:
One limitation of Eradicate is that certain nullability patterns are not expressible using simply the `Nullable` annotation.
One such pattern is using the knowledge that a function returns null when passed null, but returns an object otherwise.
The annotation `PropagatesNullable` is a variant of `Nullable` applied to parameters when their value propagates to the return value.
A method annotated
```
B m(PropagatesNullable A x) { return x == null ? x : B(x); }
```
indicates that `m` returns null if `x` is null, or an object of class `B` if the argument is not null.
Examples with multiple parameters are in the test cases.
This diff builds some infrastructure for annotation transformers: the example above represents the identity function on nullability annotations.
Reviewed By: jvillard
Differential Revision: D4705938
fbshipit-source-id: 9f6194e
master
Cristiano Calcagno
8 years ago
committed by
Facebook Github Bot
parent
69fe80346c
commit
434cfbfb15
@ -0,0 +1,23 @@
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/*
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* Copyright (c) 2017 - present Facebook, Inc.
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* All rights reserved.
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*
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* This source code is licensed under the BSD style license found in the
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* LICENSE file in the root directory of this source tree. An additional grant
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* of patent rights can be found in the PATENTS file in the same directory.
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*/
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package com.facebook.infer.annotation;
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import java.lang.annotation.ElementType;
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import java.lang.annotation.Retention;
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import java.lang.annotation.RetentionPolicy;
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import java.lang.annotation.Target;
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/**
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* Annotation to indicate that when the parameter is null, the result is also null.
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*/
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@Retention(RetentionPolicy.CLASS)
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@Target({ElementType.PARAMETER})
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public @interface PropagatesNullable {
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}
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@ -0,0 +1,129 @@
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/*
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* Copyright (c) 2013 - present Facebook, Inc.
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* All rights reserved.
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*
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* This source code is licensed under the BSD style license found in the
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* LICENSE file in the root directory of this source tree. An additional grant
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* of patent rights can be found in the PATENTS file in the same directory.
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*/
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package codetoanalyze.java.eradicate;
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import android.text.TextUtils;
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import javax.annotation.Nullable;
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import com.facebook.infer.annotation.Assertions;
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import com.facebook.infer.annotation.FalseOnNull;
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import com.facebook.infer.annotation.PropagatesNullable;
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import com.facebook.infer.annotation.TrueOnNull;
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public class CustomAnnotations {
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static class MyTextUtils {
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@TrueOnNull
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static boolean isEmpty(@Nullable java.lang.CharSequence s) {
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return s == null || s.equals("");
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}
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@FalseOnNull
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static boolean isNotEmpty(@Nullable java.lang.CharSequence s) {
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return s != null && s.length() > 0;
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}
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}
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class TestTextUtilsIsEmpty {
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void textUtilsNotIsEmpty(@Nullable CharSequence s) {
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if (!TextUtils.isEmpty(s)) {
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s.toString(); // OK
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}
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}
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void textUtilsIsEmpty(@Nullable CharSequence s) {
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if (TextUtils.isEmpty(s)) {
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s.toString(); // BAD
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}
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}
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void myTextUtilsNotIsEmpty(@Nullable CharSequence s) {
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if (!MyTextUtils.isEmpty(s)) {
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s.toString(); // OK
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}
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}
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void myTextUtilsIsEmpty(@Nullable CharSequence s) {
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if (MyTextUtils.isEmpty(s)) {
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s.toString(); // BAD
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}
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}
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void myTextUtilsIsNotEmpty(@Nullable CharSequence s) {
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if (MyTextUtils.isNotEmpty(s)) {
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s.toString(); // OK
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}
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}
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void myTextUtilsNotIsNotEmpty(@Nullable CharSequence s) {
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if (!MyTextUtils.isNotEmpty(s)) {
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s.toString(); // BAD
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}
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}
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}
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// Tests for the annotation @PropagatesNullable
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class TestPropagatesNullable {
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// one parameter: means return null iff s is null
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String m(@PropagatesNullable String s) {
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return s;
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}
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void mBad() {
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m(null).length(); // bad: m returns null
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}
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void mGood() {
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m("").length();
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}
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// limitation: we currently cannot check the body, and just trust the annotation
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String cannotCheckBody(@PropagatesNullable String s) {
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return null; // nothing is reported here
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}
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void illustrateFalseNegativeAsCannotCheckBody() {
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cannotCheckBody("").length(); // this is an NPE but is not found
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}
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// second parameter: means return null iff s2 is null
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String m2(@Nullable String s1, @PropagatesNullable String s2) {
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return s2;
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}
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void m2Bad() {
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m2(null, null).length(); // bad: m2 returns null
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}
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void m2Good() {
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m2(null, "").length();
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}
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// two parameters: means return null iff either s1 or s2 is null
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String m12(@PropagatesNullable String s1, @PropagatesNullable String s2) {
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return s1 == null ? s1 : s2;
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}
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void m12Bad1() {
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m12(null, "").length(); // bad: m12 returns null
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}
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void m12Bad2() {
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m12("", null).length(); // bad: m12 returns null
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}
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void m12Good() {
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m12("", "").length();
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}
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}
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}
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