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CatarinaGamboaclaude
CatarinaGamboa
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claude
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Model null comparisons as unknown booleans instead of true
Treating `x == null` / `x != null` as the constant `true` made the negated condition `false`, so else branches of `||` conditions were considered dead, `&&` else branches gained a false fact, and ternaries and boolean locals took a fixed value. A null comparison now becomes a fresh unconstrained boolean variable; other operands keep their facts. Adds ErrorNullLiterals (negative test) and extends CorrectNullLiterals. Refs #301 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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3 files changed

Lines changed: 63 additions & 3 deletions

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‎liquidjava-example/src/main/java/testSuite/CorrectNullLiterals.java‎

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@@ -38,4 +38,17 @@ public static void main(String[] args) throws IOException {
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int y = x + 1;
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}
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}
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// facts next to a null comparison are kept
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static void conjunction(String s, int y) {
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if (s == null && y > 0) {
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@Refinement("_ > 0")
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int z = y;
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}
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}
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static void ternary(Object o) {
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@Refinement("_ == -1 || _ == 1")
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int x = (o == null) ? -1 : 1;
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}
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}

‎liquidjava-example/src/main/java/testSuite/ErrorNullLiterals.java‎

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@@ -0,0 +1,47 @@
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package testSuite;
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import liquidjava.specification.Refinement;
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@SuppressWarnings("unused")
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public class ErrorNullLiterals {
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// comparisons with null are unknown booleans, so no branch may be considered unreachable
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static void elseBranch(String name) {
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if (name == null) {
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System.out.println("none");
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} else {
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@Refinement("_ > 0")
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int x = -1; // Expect: Refinement Error
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}
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}
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static void elseBranchOfDisjunction(String name, int y) {
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if (name == null || y > 0) {
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System.out.println("some");
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} else {
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@Refinement("_ > 0")
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int x = -1; // Expect: Refinement Error
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}
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}
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static void elseBranchOfConjunction(String name, int y) {
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if (name != null && y > 0) {
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System.out.println("some");
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} else {
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@Refinement("_ <= 0")
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int z = y; // Expect: Refinement Error
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}
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}
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static void ternary(Object o) {
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@Refinement("_ < 0")
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int x = (o == null) ? -1 : 1; // Expect: Refinement Error
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}
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static void booleanValue(Object o) {
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boolean isNull = o == null;
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@Refinement("_ == true")
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boolean b = isNull; // Expect: Refinement Error
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}
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}

‎liquidjava-verifier/src/main/java/liquidjava/processor/refinement_checker/general_checkers/OperationsChecker.java‎

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@@ -80,7 +80,7 @@ public <T> void getBinaryOpRefinements(CtBinaryOperator<T> operator) throws LJEr
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oper = getOperationRefinements(operator, parentVar, operator);
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} else if (hasNullOperand(operator)) {
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oper = new Predicate(); // comparisons with null are not supported yet, carry no information
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oper = createFreshValue(operator, new Predicate()); // null comparisons are not supported yet: unknown value
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} else {
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Predicate varLeft = getOperationRefinements(operator, left);
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Predicate varRight = getOperationRefinements(operator, right);
@@ -225,8 +225,8 @@ private Predicate getOperationRefinements(CtBinaryOperator<?> operator, CtVariab
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rtc.getContext().addVarToContext(elemName, elemVar.getType(), e, elemVar);
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return Predicate.createVar(returnName);
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} else if (element instanceof CtBinaryOperator<?> binop) {
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if (hasNullOperand(binop))
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return new Predicate();
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if (hasNullOperand(binop)) // null comparisons are not supported yet: unknown boolean value
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return createFreshValue(binop, new Predicate());
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Predicate right = getOperationRefinements(operator, parentVar, binop.getRightHandOperand());
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Predicate left = getOperationRefinements(operator, parentVar, binop.getLeftHandOperand());
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return Predicate.createOperation(left, getOperatorFromKind(binop.getKind()), right);

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