Cleanup, find new failing test case

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/ast/PolyResolution.java

@@ -278,9 +278,6 @@ final class PolyResolution {
             || e instanceof InvocationNode;
     }
 
-    // Some symbol is not resolved
-    // go backwards from the context to get it.
-
     /**
      * Fallback for some standalone expressions, that may use some context
      * to set their type. This must not trigger any type inference process
@@ -288,6 +285,9 @@ final class PolyResolution {
      * context, that context must not be called.
      */
     JTypeMirror getContextTypeForStandaloneFallback(ASTExpression e) {
+        // Some symbol is not resolved
+        // go backwards from the context to get it.
+
         // The case mentioned by the doc is removed. We could be smarter
         // with how we retry failed invocation resolution, see history
         // of this comment
@@ -556,7 +556,7 @@ final class PolyResolution {
             // means the "node" is a "stop recursion because no context" result in contextOf
             return false;
         } else if (isPreJava8()) {
-            // in java < 8, context doesn't go flow through ternaries
+            // in java < 8, context doesn't flow through ternaries
             return false;
         } else if (!internalUse
             && node instanceof ASTConditionalExpression

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/codestyle/UseDiamondOperatorRule.java

@@ -4,7 +4,6 @@
 
 package net.sourceforge.pmd.lang.java.rule.codestyle;
 
-import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
 
@@ -125,8 +124,7 @@ public class UseDiamondOperatorRule extends AbstractJavaRulechainRule {
         // this may not mutate the AST
         JavaExprMirrors factory = JavaExprMirrors.forObservation(infer);
         CtorInvocationMirror baseMirror = (CtorInvocationMirror) factory.getTopLevelInvocationMirror(ctorCall);
-        JTypeMirror newType = ctorCall.getTypeNode().getTypeMirror();
-        return new SpyInvocMirror(baseMirror, (JClassType) newType);
+        return new SpyInvocMirror(baseMirror);
     }
 
 
@@ -169,24 +167,17 @@ public class UseDiamondOperatorRule extends AbstractJavaRulechainRule {
     private static final class SpyInvocMirror implements CtorInvocationMirror {
 
         private final CtorInvocationMirror base;
-        private final JClassType modifiedNewType;
 
-        SpyInvocMirror(CtorInvocationMirror base, JClassType baseNewType) {
+        SpyInvocMirror(CtorInvocationMirror base) {
             this.base = base;
-            // see doc of CtorInvocationMirror#getNewType
-            this.modifiedNewType = baseNewType.getGenericTypeDeclaration();
         }
 
         // overridden methods
 
-        @Override
-        public void setInferredType(JTypeMirror mirror) {
-            // do nothing, we shouldn't affect the AST from here
-        }
-
         @Override
         public @NonNull JTypeMirror getNewType() {
-            return modifiedNewType;
+            // see doc of CtorInvocationMirror#getNewType
+            return ((JClassType) base.getNewType()).getGenericTypeDeclaration();
         }
 
         @Override
@@ -194,17 +185,22 @@ public class UseDiamondOperatorRule extends AbstractJavaRulechainRule {
             return true; // pretend it is
         }
 
+        // delegated methods
+
         @Override
         public List<JTypeMirror> getExplicitTypeArguments() {
-            return Collections.emptyList(); // pretend they're not there
+            return base.getExplicitTypeArguments();
         }
 
         @Override
         public JavaNode getExplicitTargLoc(int i) {
-            throw new IndexOutOfBoundsException();
+            return base.getExplicitTargLoc(i);
         }
 
-        // delegated methods
+        @Override
+        public void setInferredType(JTypeMirror mirror) {
+            base.setInferredType(mirror);
+        }
 
         @Override
         public void setCtDecl(MethodCtDecl methodType) {

pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/codestyle/xml/UseDiamondOperator.xml

@@ -292,9 +292,6 @@ public class UseDiamondOperatorFalseNegative {
         <description>Java 7 invocation context</description>
         <expected-problems>0</expected-problems>
         <code><![CDATA[
-import java.util.List;
-import java.util.ArrayList;
-
 public class Generic<T> {
     <E> Generic<E> method(Generic<E> e) { return e; }
     public Generic<T> test() {
@@ -308,14 +305,26 @@ public class Generic<T> {
         <description>Java 8+ invocation context</description>
         <expected-problems>1</expected-problems>
         <code><![CDATA[
-import java.util.List;
-import java.util.ArrayList;
-
 public class Generic<T> {
     <E> Generic<E> method(Generic<E> e) { return e; }
     public Generic<T> test() {
         return method(new Generic<T>());
     }
+}
+        ]]></code>
+    </test-code>
+    <test-code>
+        <description>Java 8+ invocation context, no target</description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[
+public class Generic<T> {
+    <E> Generic<E> method(Generic<E> e) { return e; }
+    public Generic<T> test() {
+        // todo need to create spy,
+        //  ask someone (PolyResolution?) to create enclosing mirrors,
+        //  then hand that to Infer, then unwrap
+        var m = method(new Generic<T>());
+    }
 }
         ]]></code>
     </test-code>
@@ -327,8 +336,6 @@ public class Generic<T> {
         </expected-messages>
         <code><![CDATA[
 package p;
-import java.util.List;
-import java.util.ArrayList;
 
 public class Generic<T> {
     <E> Generic<E> method(Generic<E> e) { return e; }
@@ -347,8 +354,6 @@ public class Generic<T> {
         </expected-messages>
         <code><![CDATA[
 package p;
-import java.util.List;
-import java.util.ArrayList;
 
 public class Generic<T> {
     static class Inner<K> {}