[java] Fix #5190 - NPE in type inference caused by null type (#5192)

Merge pull request #5192 from oowekyala:issue5190-npe-infer

.all-contributorsrc

@@ -7754,6 +7754,15 @@
       "contributions": [
         "bug"
       ]
+    },
+    {
+      "login": "vedantchokshi",
+      "name": "Vedant Chokshi",
+      "avatar_url": "https://avatars.githubusercontent.com/u/22137048?v=4",
+      "profile": "https://github.com/vedantchokshi",
+      "contributions": [
+        "bug"
+      ]
     }
   ],
   "contributorsPerLine": 7,

docs/pages/release_notes.md

@@ -20,6 +20,8 @@ This is a {{ site.pmd.release_type }} release.
     (ApexCRUDViolation, CognitiveComplexity, OperationWithLimitsInLoop)
   * [#5163](https://github.com/pmd/pmd/issues/5163): \[apex] Parser error when using toLabel in SOSL query
   * [#5182](https://github.com/pmd/pmd/issues/5182): \[apex] Parser error when using GROUPING in a SOQL query
+* java
+  * [#5190](https://github.com/pmd/pmd/issues/5190): \[java] NPE in type inference
 
 ### 🚨 API Changes
 

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeSystem.java

@@ -798,6 +798,11 @@ public final class TypeSystem {
             return null;
         }
 
+        @Override
+        public @Nullable JTypeMirror getAsSuper(@NonNull JClassSymbol symbol) {
+            throw new UnsupportedOperationException("Null type cannot call asSuper, will return null always");
+        }
+
         @Override
         public <T, P> T acceptVisitor(JTypeVisitor<T, P> visitor, P p) {
             return visitor.visitNullType(this, p);

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/Infer.java

@@ -816,7 +816,7 @@ public final class Infer {
 
     private boolean commonSuperWithDiffParameterization(JTypeMirror t, JTypeMirror s) {
         JTypeMirror lubResult = ts.lub(listOf(t, s));
-        if (lubResult.isBottom() || lubResult.isTop()) {
+        if (lubResult.isBottom() || lubResult.isTop() || t.isBottom() || s.isBottom()) {
             return false;
         }
         for (JTypeMirror sup : asList(lubResult)) {
@@ -824,6 +824,8 @@ public final class Infer {
                 JClassSymbol sym = ((JClassType) sup).getSymbol();
                 JTypeMirror asSuperOfT = t.getAsSuper(sym);
                 JTypeMirror asSuperOfS = s.getAsSuper(sym);
+                assert asSuperOfS != null : "s <: sup, because sup is part of the LUB of s";
+                assert asSuperOfT != null : "t <: sup, because sup is part of the LUB of t";
                 if (!asSuperOfS.equals(asSuperOfT)) {
                     return true;
                 }

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/InferenceVar.java

@@ -97,7 +97,6 @@ public final class InferenceVar implements SubstVar {
      * Adds a new bound on this variable.
      */
     public void addBound(BoundKind kind, JTypeMirror type) {
-        this.hasNonTrivialBound = true;
         addBound(kind, type, false);
     }
 
@@ -115,9 +114,15 @@ public final class InferenceVar implements SubstVar {
             // may occur because of transitive propagation
             // alpha <: alpha is always true and not interesting
             return;
+        } else if (kind == BoundKind.LOWER && type.isBottom()) {
+            // null <: alpha is not interesting and may cause errors because of lub.
+            return;
         }
 
         if (boundSet.bounds.computeIfAbsent(kind, k -> new LinkedHashSet<>()).add(type)) {
+            if (!isPrimaryBound) {
+                this.hasNonTrivialBound = true;
+            }
             ctx.onBoundAdded(this, kind, type, isPrimaryBound);
         }
     }

pmd-java/src/test/java/net/sourceforge/pmd/lang/java/types/internal/infer/InferenceCtxUnitTests.java

@@ -74,6 +74,22 @@ class InferenceCtxUnitTests extends BaseTypeInferenceUnitTest {
         verify(log).boundAdded(ctx, v2, BoundKind.UPPER, listOfV1, false);
     }
 
+
+    @Test
+    void testNullTypeCannotBeLowerBound() {
+        TypeInferenceLogger log = spy(TypeInferenceLogger.noop());
+        InferenceContext ctx = emptyCtx(log);
+
+        InferenceVar v1 = newIvar(ctx);
+
+        addSubtypeConstraint(ctx, ts.NULL_TYPE, v1);
+
+
+        assertThat(v1, hasBoundsExactly(upper(ts.OBJECT)));
+
+        verify(log, never()).boundAdded(ctx, v1, BoundKind.LOWER, ts.NULL_TYPE, false);
+    }
+
     @Test
     void testEqBoundWithGenerics() {
         TypeInferenceLogger log = spy(TypeInferenceLogger.noop());

pmd-java/src/test/kotlin/net/sourceforge/pmd/lang/java/types/internal/infer/TypeInferenceTest.kt

@@ -454,4 +454,48 @@ public class BadIntersection {
             info.methodType.formalParameters[0] shouldBe optOutEnum
         }
     }
+    parserTest("#5190 NPE in type inf") {
+        val (acu, spy) = parser.parseWithTypeInferenceSpy(
+            """
+    import java.util.Iterator;
+    interface Optional<V> {
+        static <T> Optional<T> ofNullable(T t) {}
+    }
+    interface Map<K,V> {}
+    interface List<V> extends Iterable<V> {}
+    interface AttributeValue{}
+    
+class Main {
+
+        private Optional<Map<String, AttributeValue>> loadForKey(final String key) {
+            return Optional.ofNullable(
+                getOnlyElement(queryForKey(key), null)
+            );
+        }
+
+        private List<Map<String, AttributeValue>> queryForKey(final String key) {
+            return null;
+        }
+
+        public static <T> T getOnlyElement(final Iterable<? extends T> iterable, final T defaultValue) {
+            return getOnlyElement(iterable.iterator(), defaultValue);
+        }
+
+        public static <T> T getOnlyElement(final Iterator<? extends T> iterator, final T defaultValue) {
+            return null;
+        }
+
+    }
+            """.trimIndent()
+        )
+
+        val (_, _, _) = acu.declaredTypeSignatures()
+        val (ofNullable) = acu.methodDeclarations().toList { it.genericSignature }
+
+        spy.shouldBeOk {
+            val info = acu.firstMethodCall().overloadSelectionInfo
+            info::isFailed shouldBe false
+            info.methodType shouldBeSomeInstantiationOf ofNullable
+        }
+    }
 })