Move Junit 5 assertThrows to last statement in lamdba (#590)

* Initial stab at recipe to move assertThrows to last statement in lamdba

* Silence the review bot by applying recommended changes

* Handle the non-assignment case already

* Add a note on another case to check

* Handle case where variable is declared with assertThrows

* Add test case for assertThrows with error message

* Update tests to account for removal of unnecessary curly braces. Also add warning of possible compilation error in description.

* Update warning in description

---------

Co-authored-by: Tim te Beek <[email protected]>

Author: shivanisky

src/main/java/org/openrewrite/java/testing/junit5/AssertThrowsOnLastStatement.java

@@ -0,0 +1,146 @@
+/*
+ * Copyright 2021 the original author or authors.
+ * <p>
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * <p>
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.openrewrite.java.testing.junit5;
+
+import org.openrewrite.ExecutionContext;
+import org.openrewrite.Preconditions;
+import org.openrewrite.Recipe;
+import org.openrewrite.TreeVisitor;
+import org.openrewrite.internal.ListUtils;
+import org.openrewrite.java.JavaIsoVisitor;
+import org.openrewrite.java.MethodMatcher;
+import org.openrewrite.java.search.UsesMethod;
+import org.openrewrite.java.tree.Expression;
+import org.openrewrite.java.tree.J;
+import org.openrewrite.java.tree.Statement;
+import org.openrewrite.staticanalysis.LambdaBlockToExpression;
+
+import java.util.Collections;
+import java.util.List;
+
+import static java.util.Collections.singletonList;
+
+
+public class AssertThrowsOnLastStatement extends Recipe {
+
+    @Override
+    public String getDisplayName() {
+        return "Applies Junit 5 assertThrows on last statement in lamdba block only";
+    }
+
+    @Override
+    public String getDescription() {
+        return "Applies Junit 5 assertThrows on last statement in lambda block only, in extremely rare cases may cause " +
+                "compilation errors if lambda uses non final variables.";
+    }
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor() {
+        MethodMatcher assertThrowsMatcher = new MethodMatcher(
+                "org.junit.jupiter.api.Assertions assertThrows(java.lang.Class, org.junit.jupiter.api.function.Executable, ..)");
+        return Preconditions.check(new UsesMethod<>(assertThrowsMatcher), new JavaIsoVisitor<ExecutionContext>() {
+            @Override
+            public J.MethodDeclaration visitMethodDeclaration(J.MethodDeclaration methodDecl, ExecutionContext ctx) {
+                J.MethodDeclaration m = super.visitMethodDeclaration(methodDecl, ctx);
+
+                m = m.withBody(m.getBody().withStatements(ListUtils.flatMap(m.getBody().getStatements(), methodStatement -> {
+                    J statementToCheck = methodStatement;
+                    final J.VariableDeclarations assertThrowsWithVarDec;
+                    final J.VariableDeclarations.NamedVariable assertThrowsVar;
+
+                    if (methodStatement instanceof J.VariableDeclarations) {
+                        assertThrowsWithVarDec = (J.VariableDeclarations) methodStatement;
+                        List<J.VariableDeclarations.NamedVariable> assertThrowsNamedVars = assertThrowsWithVarDec.getVariables();
+                        if (assertThrowsNamedVars.size() != 1) {
+                            return methodStatement;
+                        }
+
+                        // has variable declaration for assertThrows eg Throwable ex = assertThrows(....)
+                        assertThrowsVar = assertThrowsNamedVars.get(0);
+                        statementToCheck = assertThrowsVar.getInitializer();
+                    } else {
+                        assertThrowsWithVarDec = null;
+                        assertThrowsVar = null;
+                    }
+
+                    if (!(statementToCheck instanceof J.MethodInvocation)) {
+                        return methodStatement;
+                    }
+
+                    J.MethodInvocation methodInvocation = (J.MethodInvocation) statementToCheck;
+                    if (!assertThrowsMatcher.matches(methodInvocation)) {
+                        return methodStatement;
+                    }
+
+                    List<Expression> arguments = methodInvocation.getArguments();
+                    if (arguments.size() <= 1) {
+                        return methodStatement;
+                    }
+
+                    Expression arg = arguments.get(1);
+                    if (!(arg instanceof J.Lambda)) {
+                        return methodStatement;
+                    }
+
+                    J.Lambda lambda = (J.Lambda) arg;
+                    if (!(lambda.getBody() instanceof J.Block)) {
+                        return methodStatement;
+                    }
+
+                    J.Block body = (J.Block) lambda.getBody();
+                    if (body == null) {
+                        return methodStatement;
+                    }
+
+                    List<Statement> lambdaStatements = body.getStatements();
+                    if (lambdaStatements.size() <= 1) {
+                        return methodStatement;
+                    }
+
+                    // TODO Check to see if last line in lambda does not use a non-final variable
+
+                    // move all the statements from the body into before the method invocation, except last one
+                    return ListUtils.map(lambdaStatements, (idx, lambdaStatement) -> {
+                        if (idx < lambdaStatements.size() - 1) {
+                            return lambdaStatement.withPrefix(methodStatement.getPrefix().withComments(Collections.emptyList()));
+                        }
+
+                        J.MethodInvocation newAssertThrows = methodInvocation.withArguments(
+                                ListUtils.map(arguments, (argIdx, argument) -> {
+                                    if (argIdx == 1) {
+                                        // Only retain the last statement in the lambda block
+                                        return lambda.withBody(body.withStatements(singletonList(lambdaStatement)));
+                                    }
+                                    return argument;
+                                })
+                        );
+
+                        if (assertThrowsWithVarDec == null) {
+                            return newAssertThrows;
+                        }
+
+                        J.VariableDeclarations.NamedVariable newAssertThrowsVar = assertThrowsVar.withInitializer(newAssertThrows);
+                        return assertThrowsWithVarDec.withVariables(singletonList(newAssertThrowsVar));
+                    });
+
+                })));
+
+                doAfterVisit(new LambdaBlockToExpression().getVisitor());
+                return m;
+            }
+        });
+    }
+}