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JSpecify generics checks for conditional expressions (#739)
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For a conditional expression _e_, the type parameter nullability annotations of the true-subpart and false-subpart should match the annotations required by _e_'s context.  E.g., if _e_ is the right-hand side of an assignment, the annotations should match those for the type parameters for the assignment's left-hand side:
```java
// this is fine
A<@nullable String> t = condition? new A<@nullable String> : new A<@nullable String>();
// this is bad
A<@nullable String> t2 = condition? new A<String> : new A<String>();
// this is also bad
A<@nullable String>  t1 = condition ? new A<String>(): new A<@nullable String>()
```
Other contexts include returns, parameter passing, and being nested inside another conditional expression.  In our experience, it seems that `javac` captures the type parameter nullability required by _e_'s context in the type of _e_ itself.  So, our handling of conditional expressions simply checks that the types of both the true and false sub-expressions of _e_ are assignable to (i.e., a subtype of) the type of _e_, using the same machinery for checking assignments from #715.
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@NikitaAware
NikitaAware authored Mar 9, 2023
1 parent f743be3 commit d83b7d0
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63 changes: 63 additions & 0 deletions nullaway/src/main/java/com/uber/nullaway/GenericsChecks.java
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@
import com.sun.source.tree.AnnotatedTypeTree;
import com.sun.source.tree.AnnotationTree;
import com.sun.source.tree.AssignmentTree;
import com.sun.source.tree.ConditionalExpressionTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.NewClassTree;
import com.sun.source.tree.ParameterizedTypeTree;
Expand Down Expand Up @@ -150,6 +151,23 @@ private static void reportInvalidReturnTypeError(
errorMessage, analysis.buildDescription(tree), state, null));
}

private static void reportMismatchedTypeForTernaryOperator(
Tree tree, Type expressionType, Type subPartType, VisitorState state, NullAway analysis) {
ErrorBuilder errorBuilder = analysis.getErrorBuilder();
ErrorMessage errorMessage =
new ErrorMessage(
ErrorMessage.MessageTypes.ASSIGN_GENERIC_NULLABLE,
String.format(
"Conditional expression must have type "
+ expressionType
+ " but the sub-expression has type "
+ subPartType
+ ", which has mismatched nullability of type parameters"));
state.reportMatch(
errorBuilder.createErrorDescription(
errorMessage, analysis.buildDescription(tree), state, null));
}

/**
* This method returns the type of the given tree, including any type use annotations.
*
Expand Down Expand Up @@ -366,4 +384,49 @@ private Type.ClassType typeWithPreservedAnnotations(ParameterizedTypeTree tree)
type.getEnclosingType(), com.sun.tools.javac.util.List.from(newTypeArgs), type.tsym);
return finalType;
}

/**
* For a conditional expression <em>c</em>, check whether the type parameter nullability for each
* sub-expression of <em>c</em> matches the type parameter nullability of <em>c</em> itself.
*
* <p>Note that the type parameter nullability for <em>c</em> is computed by javac and reflects
* what is required of the surrounding context (an assignment, parameter pass, etc.). It is
* possible that both sub-expressions of <em>c</em> will have identical type parameter
* nullability, but will still not match the type parameter nullability of <em>c</em> itself, due
* to requirements from the surrounding context. In such a case, our error messages may be
* somewhat confusing; we may want to improve this in the future.
*
* @param tree A conditional expression tree to check
*/
public void checkTypeParameterNullnessForConditionalExpression(ConditionalExpressionTree tree) {
if (!config.isJSpecifyMode()) {
return;
}

Tree truePartTree = tree.getTrueExpression();
Tree falsePartTree = tree.getFalseExpression();

Type condExprType = getTreeType(tree);
Type truePartType = getTreeType(truePartTree);
Type falsePartType = getTreeType(falsePartTree);
// The condExpr type should be the least-upper bound of the true and false part types. To check
// the nullability annotations, we check that the true and false parts are assignable to the
// type of the whole expression
if (condExprType instanceof Type.ClassType) {
if (truePartType instanceof Type.ClassType) {
if (!compareNullabilityAnnotations(
(Type.ClassType) condExprType, (Type.ClassType) truePartType)) {
reportMismatchedTypeForTernaryOperator(
truePartTree, condExprType, truePartType, state, analysis);
}
}
if (falsePartType instanceof Type.ClassType) {
if (!compareNullabilityAnnotations(
(Type.ClassType) condExprType, (Type.ClassType) falsePartType)) {
reportMismatchedTypeForTernaryOperator(
falsePartTree, condExprType, falsePartType, state, analysis);
}
}
}
}
}
2 changes: 2 additions & 0 deletions nullaway/src/main/java/com/uber/nullaway/NullAway.java
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Expand Up @@ -1493,6 +1493,8 @@ public Description matchUnary(UnaryTree tree, VisitorState state) {
public Description matchConditionalExpression(
ConditionalExpressionTree tree, VisitorState state) {
if (withinAnnotatedCode(state)) {
new GenericsChecks(state, config, this)
.checkTypeParameterNullnessForConditionalExpression(tree);
doUnboxingCheck(state, tree.getCondition());
}
return Description.NO_MATCH;
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105 changes: 105 additions & 0 deletions nullaway/src/test/java/com/uber/nullaway/NullAwayJSpecifyGenericsTests.java
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Expand Up @@ -557,6 +557,111 @@ public void genericFunctionReturnTypeMultipleReturnStatementsIfElseBlock() {
.doTest();
}

@Test
public void genericsChecksForTernaryOperator() {
makeHelper()
.addSourceLines(
"Test.java",
"package com.uber;",
"import org.jspecify.annotations.Nullable;",
"class Test {",
"static class A<T extends @Nullable Object> { }",
" static A<String> testPositive(A<String> a, boolean t) {",
" // BUG: Diagnostic contains: Conditional expression must have type",
" A<@Nullable String> t1 = t ? new A<String>() : new A<@Nullable String>();",
" // BUG: Diagnostic contains: Conditional expression must have type",
" return t ? new A<@Nullable String>() : new A<@Nullable String>();",
" }",
" static void testPositiveTernaryMethodArgument(boolean t) {",
" // BUG: Diagnostic contains: Conditional expression must have type",
" A<String> a = testPositive(t ? new A<String>() : new A<@Nullable String>(), t);",
" }",
" static A<@Nullable String> testNegative(boolean t) {",
" A<@Nullable String> t1 = t ? new A<@Nullable String>() : new A<@Nullable String>();",
" return t ? new A<@Nullable String>() : new A<@Nullable String>();",
" }",
"}")
.doTest();
}

@Test
public void ternaryOperatorComplexSubtyping() {
makeHelper()
.addSourceLines(
"Test.java",
"package com.uber;",
"import org.jspecify.annotations.Nullable;",
"class Test {",
" static class A<T extends @Nullable Object> {}",
" static class B<T extends @Nullable Object> extends A<T> {}",
" static class C<T extends @Nullable Object> extends A<T> {}",
" static void testPositive(boolean t) {",
" // BUG: Diagnostic contains: Conditional expression must have type",
" A<@Nullable String> t1 = t ? new B<@Nullable String>() : new C<String>();",
" // BUG: Diagnostic contains: Conditional expression must have type",
" A<@Nullable String> t2 = t ? new C<String>() : new B<@Nullable String>();",
" // BUG: Diagnostic contains:Conditional expression must have type",
" A<@Nullable String> t3 = t ? new B<String>() : new C<@Nullable String>();",
" // BUG: Diagnostic contains: Conditional expression must have type",
" A<String> t4 = t ? new B<@Nullable String>() : new C<@Nullable String>();",
" }",
" static void testNegative(boolean t) {",
" A<@Nullable String> t1 = t ? new B<@Nullable String>() : new C<@Nullable String>();",
" A<@Nullable String> t2 = t ? new C<@Nullable String>() : new B<@Nullable String>();",
" A<String> t3 = t ? new C<String>() : new B<String>();",
" }",
"}")
.doTest();
}

@Test
public void nestedTernary() {
makeHelper()
.addSourceLines(
"Test.java",
"package com.uber;",
"import org.jspecify.annotations.Nullable;",
"class Test {",
" static class A<T extends @Nullable Object> {}",
" static class B<T extends @Nullable Object> extends A<T> {}",
" static class C<T extends @Nullable Object> extends A<T> {}",
" static void testPositive(boolean t) {",
" A<@Nullable String> t1 = t ? new C<@Nullable String>() :",
" // BUG: Diagnostic contains: Conditional expression must have type",
" (t ? new B<@Nullable String>() : new A<String>());",
" }",
" static void testNegative(boolean t) {",
" A<@Nullable String> t1 = t ? new C<@Nullable String>() :",
" (t ? new B<@Nullable String>() : new A<@Nullable String>());",
" }",
"}")
.doTest();
}

@Test
public void ternaryMismatchedAssignmentContext() {
makeHelper()
.addSourceLines(
"Test.java",
"package com.uber;",
"import org.jspecify.annotations.Nullable;",
"class Test {",
"static class A<T extends @Nullable Object> { }",
" static void testPositive(boolean t) {",
" // we get two errors here, one for each sub-expression; perhaps ideally we would report",
" // just one error (that the ternary operator has type A<String> but the assignment LHS",
" // has type A<@Nullable String>), but implementing that check in general is",
" // a bit tricky",
" A<@Nullable String> t1 = t",
" // BUG: Diagnostic contains: Conditional expression must have type",
" ? new A<String>()",
" // BUG: Diagnostic contains: Conditional expression must have type",
" : new A<String>();",
" }",
"}")
.doTest();
}

private CompilationTestHelper makeHelper() {
return makeTestHelperWithArgs(
Arrays.asList(
Expand Down

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