Fix JavaTemplate replacements passing a J.NewArray into a vararg J.MethodInvocation (#6572)

* JavaTemplate vararg replacement should not contain excess braces

* Expand `J.NewArray` passed directly into `J.MethodInvocation`

* Adopt `ListUtils` for expansion

Author: timtebeek

rewrite-java-test/src/test/java/org/openrewrite/java/JavaTemplateSubstitutionsTest.java

@@ -551,4 +551,51 @@ public J visitMethodInvocation(J.MethodInvocation method, ExecutionContext ctx)
             return m;
         }
     }
+
+    @Test
+    void changeVarargsToList() {
+        rewriteRun(
+          // Mimics what a Refaster template would generate for varargs
+          spec -> spec.recipe(toRecipe(() -> new JavaVisitor<>() {
+              @Override
+              public J visitMethodInvocation(J.MethodInvocation elem, ExecutionContext ctx) {
+                  JavaTemplate.Matcher matcher;
+                  JavaTemplate before = JavaTemplate.builder("java.util.stream.Stream.of(#{value:anyArray(T)}).toList()")
+                    .bindType("java.util.List<T>")
+                    .genericTypes("T").build();
+                  if ((matcher = before.matcher(getCursor())).find()) {
+                      maybeRemoveImport("java.util.stream.Stream");
+                      return JavaTemplate.builder("java.util.Arrays.asList(#{value:anyArray(T)})")
+                        .bindType("java.util.List<T>")
+                        .genericTypes("T")
+                        .build()
+                        .apply(getCursor(), elem.getCoordinates().replace(), matcher.parameter(0));
+                  }
+                  return super.visitMethodInvocation(elem, ctx);
+              }
+          })),
+          //language=java
+          java(
+            """
+              import java.util.List;
+              import java.util.stream.Stream;
+              
+              class Example {
+                  List<String> test() {
+                      return Stream.of("a", "b", "c").toList();
+                  }
+              }
+              """,
+            """
+              import java.util.List;
+              
+              class Example {
+                  List<String> test() {
+                      return java.util.Arrays.asList("a", "b", "c");
+                  }
+              }
+              """
+          )
+        );
+    }
 }

rewrite-java/src/main/java/org/openrewrite/java/internal/template/Substitutions.java

@@ -298,7 +298,22 @@ public J visitMethodInvocation(J.MethodInvocation method, Integer integer) {
                 } else if (param != null) {
                     return param;
                 }
-                return super.visitMethodInvocation(method, integer);
+
+                J.MethodInvocation m = (J.MethodInvocation) super.visitMethodInvocation(method, integer);
+                return maybeExpandVarargsNewArray(m);
+            }
+
+            private J.MethodInvocation maybeExpandVarargsNewArray(J.MethodInvocation method) {
+                return method.withArguments(ListUtils.flatMap(method.getArguments(), arg -> {
+                    if (arg instanceof J.NewArray) {
+                        J.NewArray newArray = (J.NewArray) arg;
+                        // Varargs-captured arrays have no type expression and no dimensions
+                        if (newArray.getTypeExpression() == null && newArray.getDimensions().isEmpty()) {
+                            return ListUtils.mapFirst(newArray.getInitializer(), e -> e.withPrefix(newArray.getPrefix()));
+                        }
+                    }
+                    return arg;
+                }));
             }
 
             @Override