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Add BugPattern to rewrite assertThat(...).isEqualTo(null) to assertThat(...).isNull() #133

Merged
merged 10 commits into from
Jun 29, 2022
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package tech.picnic.errorprone.bugpatterns;

import static com.google.errorprone.BugPattern.LinkType.NONE;
import static com.google.errorprone.BugPattern.SeverityLevel.SUGGESTION;
import static com.google.errorprone.BugPattern.StandardTags.SIMPLIFICATION;
import static com.google.errorprone.matchers.Matchers.allOf;
import static com.google.errorprone.matchers.Matchers.argument;
import static com.google.errorprone.matchers.Matchers.argumentCount;
import static com.google.errorprone.matchers.Matchers.instanceMethod;
import static com.google.errorprone.matchers.Matchers.nullLiteral;

import com.google.auto.service.AutoService;
import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker;
import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
import com.google.errorprone.fixes.SuggestedFix;
import com.google.errorprone.fixes.SuggestedFixes;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.matchers.Matcher;
import com.sun.source.tree.MethodInvocationTree;

/**
* A {@link BugChecker} which flags AssertJ {@code isEqualTo(null)} checks for simplification.
*
* <p>This bug checker cannot be replaced with a simple Refaster template, as the Refaster approach
* would require that all overloads of {@link org.assertj.core.api.Assert#isEqualTo(Object)} (such
* as {@link org.assertj.core.api.AbstractStringAssert#isEqualTo(String)}) are explicitly
* enumerated. This bug checker generically matches all such current and future overloads.
*/
@AutoService(BugChecker.class)
@BugPattern(
name = "AssertJIsNull",
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summary = "Prefer `.isNull()` over `.isEqualTo(null)`",
linkType = NONE,
severity = SUGGESTION,
tags = SIMPLIFICATION)
public final class AssertJIsNullCheck extends BugChecker implements MethodInvocationTreeMatcher {
private static final long serialVersionUID = 1L;
private static final Matcher<MethodInvocationTree> ASSERT_IS_EQUAL_TO_NULL =
allOf(
instanceMethod().onDescendantOf("org.assertj.core.api.Assert").named("isEqualTo"),
argumentCount(1),
argument(0, nullLiteral()));

@Override
public Description matchMethodInvocation(MethodInvocationTree tree, VisitorState state) {
if (!ASSERT_IS_EQUAL_TO_NULL.matches(tree, state)) {
return Description.NO_MATCH;
}

SuggestedFix.Builder fix =
SuggestedFix.builder().merge(SuggestedFixes.renameMethodInvocation(tree, "isNull", state));
tree.getArguments().forEach(arg -> fix.merge(SuggestedFix.delete(arg)));

return describeMatch(tree, fix.build());
}
}
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package tech.picnic.errorprone.bugpatterns;

import static com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode.TEXT_MATCH;

import com.google.errorprone.BugCheckerRefactoringTestHelper;
import com.google.errorprone.CompilationTestHelper;
import org.junit.jupiter.api.Test;

final class AssertJIsNullCheckTest {
private final CompilationTestHelper compilationTestHelper =
CompilationTestHelper.newInstance(AssertJIsNullCheck.class, getClass());
private final BugCheckerRefactoringTestHelper refactoringTestHelper =
BugCheckerRefactoringTestHelper.newInstance(AssertJIsNullCheck.class, getClass());

@Test
void identification() {
compilationTestHelper
.addSourceLines(
"A.java",
"import static org.assertj.core.api.Assertions.assertThat;",
"",
"class A {",
" void m() {",
" assertThat(1).isEqualTo(1);",
" // BUG: Diagnostic contains:",
" assertThat(1).isEqualTo(null);",
" // BUG: Diagnostic contains:",
" assertThat(\"foo\").isEqualTo(null);",
" isEqualTo(null);",
" }",
"",
" private boolean isEqualTo(Object value) {",
" return value.equals(\"bar\");",
" }",
"}")
.doTest();
}

@Test
void replacement() {
refactoringTestHelper
.addInputLines(
"A.java",
"import static org.assertj.core.api.Assertions.assertThat;",
"",
"class A {",
" void m() {",
" assertThat(1).isEqualTo(null);",
" assertThat(\"foo\").isEqualTo(null);",
" }",
"}")
.addOutputLines(
"A.java",
"import static org.assertj.core.api.Assertions.assertThat;",
"",
"class A {",
" void m() {",
" assertThat(1).isNull();",
" assertThat(\"foo\").isNull();",
" }",
"}")
.doTest(TEXT_MATCH);
}
}