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Retain necessary null checks in EqualsAvoidsNull #761

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Merged
merged 5 commits into from
Oct 24, 2025
Merged

Retain necessary null checks in EqualsAvoidsNull #761

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08e1ab8
Retain necessary null checks in EqualsAvoidsNull
timtebeek Oct 24, 2025
939c413
Only remove redundant null checks
timtebeek Oct 24, 2025
82dab8d
Drop `doAfterVisit`
timtebeek Oct 24, 2025
4c67409
Clarify that annotations do not factor in
timtebeek Oct 24, 2025
5f6bbc3
Add unlikely but missing condition
timtebeek Oct 24, 2025
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94 changes: 41 additions & 53 deletions src/main/java/org/openrewrite/staticanalysis/EqualsAvoidsNull.java
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Original file line number Diff line number Diff line change
Expand Up @@ -80,25 +80,45 @@ public TreeVisitor<?, ExecutionContext> getVisitor() {
new JavaVisitor<ExecutionContext>() {
@Override
public J visitMethodInvocation(J.MethodInvocation method, ExecutionContext ctx) {
J.MethodInvocation m = (J.MethodInvocation) super.visitMethodInvocation(method, ctx);
J.MethodInvocation mi = (J.MethodInvocation) super.visitMethodInvocation(method, ctx);

if (!isStringComparisonMethod(m)) {
return m;
if (mi.getSelect() instanceof J.Literal || !isStringComparisonMethod(mi) || !hasCompatibleArgument(mi)) {
return mi;
}

// Always check for redundant null checks, even if we won't swap arguments
maybeHandleParentBinary(m, getCursor().getParentTreeCursor().getValue());
Expression firstArgument = mi.getArguments().get(0);
return firstArgument.getType() == JavaType.Primitive.Null ?
literalsFirstInComparisonsNull(mi, firstArgument) :
literalsFirstInComparisons(mi, firstArgument);
}

if (!hasCompatibleArgument(m) || m.getSelect() instanceof J.Literal) {
return m;
@Override
public J visitBinary(J.Binary binary, ExecutionContext ctx) {
// First swap order of method invocation select and argument
J.Binary b = (J.Binary) super.visitBinary(binary, ctx);

// Independent of changes above, clear out unnecessary null comparisons
if (b.getLeft() instanceof J.Binary &&
b.getOperator() == J.Binary.Type.And &&
isStringComparisonMethod(b.getRight())) {
Expression nullCheckedLeft = nullCheckedArgument((J.Binary) b.getLeft());
if (nullCheckedLeft != null && areEqual(nullCheckedLeft, ((J.MethodInvocation) b.getRight()).getArguments().get(0))) {
return b.getRight().withPrefix(b.getPrefix());
}
}
return b;
}

Expression firstArgument = m.getArguments().get(0);

return firstArgument.getType() == JavaType.Primitive.Null ?
literalsFirstInComparisonsNull(m, firstArgument) :
literalsFirstInComparisons(m, firstArgument);

private @Nullable Expression nullCheckedArgument(J.Binary binary) {
if (binary.getOperator() == J.Binary.Type.NotEqual) {
if (isLiteralValue(binary.getLeft(), null)) {
return binary.getRight();
}
if (isLiteralValue(binary.getRight(), null)) {
return binary.getLeft();
}
}
return null;
}

private boolean hasCompatibleArgument(J.MethodInvocation m) {
Expand All @@ -119,47 +139,15 @@ private boolean hasCompatibleArgument(J.MethodInvocation m) {
return false;
}

private boolean isStringComparisonMethod(J.MethodInvocation methodInvocation) {
return EQUALS_STRING.matches(methodInvocation) ||
(EQUALS_OBJECT.matches(methodInvocation) && TypeUtils.isString(methodInvocation.getArguments().get(0).getType())) ||
EQUALS_IGNORE_CASE.matches(methodInvocation) ||
CONTENT_EQUALS.matches(methodInvocation);
}

private void maybeHandleParentBinary(J.MethodInvocation m, final Tree parent) {
if (parent instanceof J.Binary) {
if (((J.Binary) parent).getOperator() == J.Binary.Type.And &&
((J.Binary) parent).getLeft() instanceof J.Binary) {
J.Binary potentialNullCheck = (J.Binary) ((J.Binary) parent).getLeft();
boolean nullCheckMatchesSelect =
(isLiteralValue(potentialNullCheck.getLeft(), null) && areEqual(potentialNullCheck.getRight(), m.getSelect())) ||
(isLiteralValue(potentialNullCheck.getRight(), null) && areEqual(potentialNullCheck.getLeft(), m.getSelect()));
boolean nullCheckMatchesArgument =
(isLiteralValue(potentialNullCheck.getLeft(), null) && areEqual(potentialNullCheck.getRight(), m.getArguments().get(0))) ||
(isLiteralValue(potentialNullCheck.getRight(), null) && areEqual(potentialNullCheck.getLeft(), m.getArguments().get(0)));
if (nullCheckMatchesSelect || nullCheckMatchesArgument) {
doAfterVisit(new JavaVisitor<ExecutionContext>() {

private final J.Binary scope = (J.Binary) parent;
private boolean done;

@Override
public @Nullable J visit(@Nullable Tree tree, ExecutionContext ctx) {
return done ? (J) tree : super.visit(tree, ctx);
}

@Override
public J visitBinary(J.Binary binary, ExecutionContext ctx) {
if (scope.isScope(binary)) {
done = true;
return binary.getRight().withPrefix(binary.getPrefix());
}
return super.visitBinary(binary, ctx);
}
});
}
}
private boolean isStringComparisonMethod(J j) {
if (j instanceof J.MethodInvocation) {
J.MethodInvocation mi = (J.MethodInvocation) j;
return EQUALS_STRING.matches(mi) ||
(EQUALS_OBJECT.matches(mi) && TypeUtils.isString(mi.getArguments().get(0).getType())) ||
EQUALS_IGNORE_CASE.matches(mi) ||
CONTENT_EQUALS.matches(mi);
}
return false;
}

private J.Binary literalsFirstInComparisonsNull(J.MethodInvocation m, Expression firstArgument) {
Expand Down
51 changes: 39 additions & 12 deletions src/test/java/org/openrewrite/staticanalysis/EqualsAvoidsNullTest.java
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -87,23 +87,50 @@ void removeUnnecessaryNullCheck() {
java(
"""
public class A {
{
String s = null, t = null;
if(s != null && s.equals("test")) {}
if(null != s && s.equals("test")) {}
if(t != null && "test".equals(t)) {}
if(null != t && "test".equals(t)) {}
void check(String s, String t) {
if (s != null && s.equals("test")) {}
if (null != s && s.equals("test")) {}
if (t != null && "test".equals(t)) {}
if (null != t && "test".equals(t)) {}
}
}
""",
"""
public class A {
{
String s = null, t = null;
if("test".equals(s)) {}
if("test".equals(s)) {}
if("test".equals(t)) {}
if("test".equals(t)) {}
void check(String s, String t) {
if ("test".equals(s)) {}
if ("test".equals(s)) {}
if ("test".equals(t)) {}
if ("test".equals(t)) {}
}
}
"""
)
);
}

@Test
void retainNecessaryNullCheck() {
rewriteRun(
//language=java
java(
"""
class A {
void check(String expected, String actual){
if (expected != null && expected.equals(actual)) {}
if (actual != null && actual.equals(expected)) {}
if (expected != null && actual.equals(expected)) {}
if (actual != null && expected.equals(actual)) {}
}
}
""",
"""
class A {
void check(String expected, String actual){
if (expected != null && expected.equals(actual)) {}
if (actual != null && actual.equals(expected)) {}
if (actual.equals(expected)) {}
if (expected.equals(actual)) {}
}
}
"""
Expand Down