[java] Fix #5097 - problem with unchecked conversion

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

@@ -717,6 +717,12 @@ public final class TypeOps {
                 // no unchecked warning.
                 return allArgsAreUnboundedWildcards(sargs) ? Convertibility.UNCHECKED_NO_WARNING
                                                            : Convertibility.UNCHECKED_WARNING;
+            } else if (sargs.isEmpty()) {
+                // C<T1...TN> <: |C|
+                // JLS 4.10.2
+                // unchecked conversion converts a raw type to a generic type
+                // subtyping converts a generic type to its raw type
+                return Convertibility.SUBTYPING;
             }
 
             if (targs.size() != sargs.size()) {

pmd-java/src/test/kotlin/net/sourceforge/pmd/lang/java/types/SubtypingTest.kt

@@ -13,14 +13,14 @@ import io.kotest.property.Exhaustive
 import io.kotest.property.checkAll
 import io.kotest.property.exhaustive.ints
 import io.kotest.property.forAll
-import net.sourceforge.pmd.lang.test.ast.shouldBeA
 import net.sourceforge.pmd.lang.java.ast.ParserTestCtx
 import net.sourceforge.pmd.lang.java.symbols.internal.UnresolvedClassStore
 import net.sourceforge.pmd.lang.java.symbols.internal.asm.createUnresolvedAsmSymbol
-import net.sourceforge.pmd.lang.java.types.TypeConversion.*
-import net.sourceforge.pmd.lang.java.types.TypeOps.Convertibility.*
+import net.sourceforge.pmd.lang.java.types.TypeConversion.capture
+import net.sourceforge.pmd.lang.java.types.TypeOps.Convertibility.UNCHECKED_NO_WARNING
 import net.sourceforge.pmd.lang.java.types.testdata.ComparableList
 import net.sourceforge.pmd.lang.java.types.testdata.SomeEnum
+import net.sourceforge.pmd.lang.test.ast.shouldBeA
 import kotlin.test.assertTrue
 
 /**
@@ -187,6 +187,9 @@ class SubtypingTest : FunSpec({
                 Class shouldBeUncheckedSubtypeOf `Class{String}`
 
                 ts.STRING shouldBeSubtypeOf `Comparable{Wildcard}`
+
+                val unresolvedT = ts.createUnresolvedAsmSymbol("foo")
+                unresolvedT[`?`] shouldBeSubtypeOf ts.rawType(unresolvedT)
             }
 
             test("Test wildcard subtyping") {

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

@@ -702,4 +702,39 @@ class C {
             buildItem.methodType.symbol shouldBe buildItemDecl
         }
     }
+
+    parserTest("Unresolved type should also allow unchecked conversion") {
+        // The problem here is that ConstraintViolation<?> is not convertible to ConstraintViolation,
+        // because ConstraintViolation is not on the classpath.
+
+        val (acu, _) = parser.parseWithTypeInferenceSpy(
+            """
+            import java.util.Set;
+            class Foo {
+                private void foo(ConstraintViolation constraintViolation) {
+                    constraintViolation.toString();
+                }
+
+                public void foos(Set<ConstraintViolation<?>> constraintViolations) {
+                    constraintViolations.forEach(this::foo);
+                }
+
+            }
+                """
+        )
+
+//        val (foreach) = acu.methodCalls().toList()
+        val constraintViolationT = acu.descendants(ASTClassType::class.java)
+            .filter { it.simpleName == "ConstraintViolation" }
+            .firstOrThrow().typeMirror.symbol as JClassSymbol
+        val (fooDecl) = acu.methodDeclarations().toList { it.symbol }
+        val (mref) = acu.descendants(ASTMethodReference::class.java).toList()
+
+        acu.withTypeDsl {
+            mref.referencedMethod.symbol shouldBe fooDecl
+
+            mref shouldHaveType java.util.function.Consumer::class[constraintViolationT[`?`]]
+
+        }
+    }
 })

pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/bestpractices/xml/UnusedPrivateMethod.xml

@@ -2218,4 +2218,36 @@ public class ObtainViaTest {
             }
             ]]></code>
     </test-code>
+    <test-code>
+        <description>#5097 UnusedPrivateMethod with unresolved target for method reference</description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[package com.mytest;
+
+        import jakarta.validation.ConstraintViolation; //imported from jakarta.validation:jakarta.validation-api:3.0.2
+        import java.util.List;
+        import java.util.Set;
+
+        public class UnusedPrivateMethodFalsePositive {
+            //this does not trigger UnusedPrivateMethod
+            private void doWork(List obj) {
+                obj.toString();
+            }
+
+            public void execute(Set<List<?>> listOfLists) {
+                listOfLists.forEach(this::doWork);
+            }
+
+            //BUT this does???
+            //UnusedPrivateMethod -  this as a false positive - but what is different?
+            private void addValidationError(ConstraintViolation constraintViolation) {
+                constraintViolation.toString();
+            }
+
+            public void addValidationErrors(Set<ConstraintViolation<?>> constraintViolations) {
+                constraintViolations.forEach(this::addValidationError);
+            }
+
+        }
+            ]]></code>
+    </test-code>
 </test-data>