Fix IndexOutOfBoundsException with lambda that has wrong shape

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

@@ -110,6 +110,13 @@ public final class ASTLambdaExpression extends AbstractJavaExpr implements Funct
     }
 
 
+    /**
+     * Returns the number of formal parameters of this lambda.
+     */
+    public int getArity() {
+        return getParameters().size();
+    }
+
     @Override
     protected <P, R> R acceptVisitor(JavaVisitor<? super P, ? extends R> visitor, P data) {
         return visitor.visit(this, data);

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

@@ -41,6 +41,12 @@ public final class ASTLambdaParameter extends AbstractJavaTypeNode
         return visitor.visit(this, data);
     }
 
+    /**
+     * Returns the lambda that owns this parameter.
+     */
+    public ASTLambdaExpression getOwner() {
+        return (ASTLambdaExpression) getParent().getParent();
+    }
 
     /**
      * Returns the declarator ID of this formal parameter.

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/ast/LazyTypeResolver.java

@@ -565,6 +565,9 @@ public final class LazyTypeResolver extends JavaVisitorBase<TypingContext, @NonN
 
         JMethodSig m = lambda.getFunctionalMethod(); // this forces resolution of the lambda
         if (!isUnresolved(m)) {
+            if (m.getArity() != node.getOwner().getArity()) {
+                return ts.ERROR;
+            }
             return m.getFormalParameters().get(node.getIndexInParent());
         }
         return ts.UNKNOWN;

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

@@ -629,4 +629,28 @@ class C {
         }
     }
 
+    parserTest("Lambda with wrong form") {
+
+        val (acu, _) = parser.parseWithTypeInferenceSpy("""
+                interface Lambda {
+                    void call();
+                }
+                class Foo {
+                    {
+                        Lambda l = () -> {}; // ok
+                        Lambda l = x -> {};  // wrong form!
+                    }
+                }
+        """)
+
+        val (ok, wrong) = acu.descendants(ASTLambdaExpression::class.java).toList()
+        val t_Lambda = acu.typeDeclarations.firstOrThrow().typeMirror
+
+        acu.withTypeDsl {
+            ok shouldHaveType t_Lambda
+            wrong shouldHaveType t_Lambda
+            wrong.parameters[0] shouldHaveType ts.ERROR
+        }
+    }
+
 })

pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/errorprone/xml/ReturnEmptyCollectionRatherThanNull.xml

@@ -191,7 +191,7 @@ import java.util.concurrent.*;
 import java.nio.file.Path;
 
 public class Foo {
-    private Map<Path, List<String>> joinFutures(Map<String, List<Future<String>>> map) {
+    private Map<String, List<String>> joinFutures(Map<String, List<Future<String>>> map) {
         Map<String, List<String>> joined = new HashMap<>();
 
         for (String p : map.keySet()) {
@@ -214,7 +214,7 @@ public class Foo {
         }
 
         // checking basic lambdas and anonymous classes as well
-        Callable<Object> c = a -> { return null; }; // <----- false positive here
+        Callable<Object> c = () -> { return null; }; // <----- false positive here
         Callable<Object> c2 = new Callable<Object>() {
             public Object call() {
                 return null; // <----- false positive here