Rewrite Joiner.on(", ").join("a", "b") to `String.join(", ", "a", "…

…b")` (#389)

* Rewrite `Joiner.on(", ").join("a", "b")` to `String.join(", ", "a", "b")`

Adds a recipe to rewrite calls to Guava Joiner#join with String.join in compatible cases. A call can be re-written if the delimiter is a String, and the arguments are an array, a list or an iterable of items that can be cast to a CharSequence.

Addresses #318

* Use `JavaTemplate` instead

---------

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

src/main/java/org/openrewrite/java/migrate/guava/PreferJavaStringJoin.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2024 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.migrate.guava;
+
+import java.util.Collections;
+import java.util.Set;
+import org.openrewrite.ExecutionContext;
+import org.openrewrite.Preconditions;
+import org.openrewrite.Recipe;
+import org.openrewrite.TreeVisitor;
+import org.openrewrite.java.MethodMatcher;
+import org.openrewrite.java.search.UsesMethod;
+
+public class PreferJavaStringJoin extends Recipe {
+
+    static final MethodMatcher JOIN_METHOD_MATCHER = new MethodMatcher("com.google.common.base.Joiner join(..)");
+
+    @Override
+    public String getDisplayName() {
+        return "Prefer `String#join()` over Guava `Joiner#join()`";
+    }
+
+    @Override
+    public String getDescription() {
+        return "Replaces supported calls to `com.google.common.base.Joiner#join()` with `java.lang.String#join()`.";
+    }
+
+    @Override
+    public Set<String> getTags() {
+        return Collections.singleton("guava");
+    }
+
+    @Override
+    public TreeVisitor<?, ExecutionContext> getVisitor() {
+        return Preconditions.check(new UsesMethod<>(JOIN_METHOD_MATCHER), new PreferJavaStringJoinVisitor());
+    }
+}

src/main/java/org/openrewrite/java/migrate/guava/PreferJavaStringJoinVisitor.java

@@ -0,0 +1,107 @@
+/*
+ * Copyright 2024 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.migrate.guava;
+
+import org.openrewrite.ExecutionContext;
+import org.openrewrite.internal.lang.Nullable;
+import org.openrewrite.java.JavaIsoVisitor;
+import org.openrewrite.java.JavaTemplate;
+import org.openrewrite.java.MethodMatcher;
+import org.openrewrite.java.tree.Expression;
+import org.openrewrite.java.tree.J;
+import org.openrewrite.java.tree.JavaType;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.openrewrite.java.migrate.guava.PreferJavaStringJoin.JOIN_METHOD_MATCHER;
+import static org.openrewrite.java.tree.TypeUtils.isAssignableTo;
+import static org.openrewrite.java.tree.TypeUtils.isString;
+
+class PreferJavaStringJoinVisitor extends JavaIsoVisitor<ExecutionContext> {
+    private static final MethodMatcher ON_METHOD_MATCHER =
+        new MethodMatcher("com.google.common.base.Joiner on(String)");
+
+    @Override
+    public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, ExecutionContext ctx) {
+        J.MethodInvocation mi = super.visitMethodInvocation(method, ctx);
+
+        if (!JOIN_METHOD_MATCHER.matches(mi) || !(mi.getSelect() instanceof J.MethodInvocation) || !ON_METHOD_MATCHER.matches(mi.getSelect())) {
+            return mi;
+        }
+
+        boolean rewriteToJavaString = false;
+
+        List<Expression> arguments = mi.getArguments();
+        if (arguments.size() == 1) {
+            JavaType javaType = arguments.get(0).getType();
+
+            rewriteToJavaString = isCompatibleArray(javaType) || isCompatibleIterable(javaType);
+        } else if (arguments.size() >= 2) {
+            rewriteToJavaString = isCompatibleArguments(arguments);
+        }
+
+        if (rewriteToJavaString) {
+            J.MethodInvocation select = (J.MethodInvocation) mi.getSelect();
+            assert select != null;
+            List<Expression> newArgs = appendArguments(select.getArguments(), mi.getArguments());
+
+            maybeRemoveImport("com.google.common.base.Joiner");
+
+            J.MethodInvocation x = JavaTemplate.apply(
+                    "String.join(#{any(java.lang.CharSequence)}",
+                    getCursor(),
+                    mi.getCoordinates().replace(),
+                    select.getArguments().get(0)
+            );
+            return x.withArguments(newArgs);
+        }
+        return mi;
+    }
+
+    private boolean isCompatibleArguments(List<Expression> arguments) {
+        return arguments.stream().map(Expression::getType).allMatch(PreferJavaStringJoinVisitor::isCharSequence);
+    }
+
+    private boolean isCompatibleArray(@Nullable JavaType javaType) {
+        if (javaType instanceof JavaType.Array) {
+            return isCharSequence(((JavaType.Array) javaType).getElemType());
+        }
+        return false;
+    }
+
+    private boolean isCompatibleIterable(@Nullable JavaType javaType) {
+        if (isAssignableTo(Iterable.class.getName(), javaType) && javaType instanceof JavaType.Parameterized) {
+            List<JavaType> typeParameters = ((JavaType.Parameterized) javaType).getTypeParameters();
+            return typeParameters.size() == 1 && isCharSequence(typeParameters.get(0));
+        }
+        return false;
+    }
+
+    private static boolean isCharSequence(@Nullable JavaType javaType) {
+        return isString(javaType) || isAssignableTo(CharSequence.class.getName(), javaType);
+    }
+
+    private List<Expression> appendArguments(List<Expression> firstArgs, List<Expression> secondArgs) {
+        ArrayList<Expression> args = new ArrayList<>(firstArgs);
+        if (!secondArgs.isEmpty()) {
+            Expression e = secondArgs.remove(0);
+            args.add(e.withPrefix(e.getPrefix().withWhitespace(" ")));
+            args.addAll(secondArgs);
+        }
+        return args;
+    }
+}

src/test/java/org/openrewrite/java/migrate/guava/PreferJavaStringJoinTest.java

@@ -0,0 +1,204 @@
+/*
+ * Copyright 2024 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.migrate.guava;
+
+import org.junit.jupiter.api.Test;
+import org.openrewrite.java.JavaParser;
+import org.openrewrite.test.RecipeSpec;
+import org.openrewrite.test.RewriteTest;
+
+import static org.openrewrite.java.Assertions.java;
+
+class PreferJavaStringJoinTest implements RewriteTest {
+    @Override
+    public void defaults(RecipeSpec spec) {
+        spec
+          .recipe(new PreferJavaStringJoin())
+          .parser(JavaParser.fromJavaVersion().classpath("guava"));
+    }
+
+    @Test
+    void joinStrings() {
+        //language=java
+        rewriteRun(
+          java(
+            """
+              import com.google.common.base.Joiner;
+                            
+              class Test {
+                  String s = Joiner.on(", ").join("a", "b");
+              }
+              """,
+            """                            
+              class Test {
+                  String s = String.join(", ", "a", "b");
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void joinStringArray() {
+        //language=java
+        rewriteRun(
+          java(
+            """
+              import com.google.common.base.Joiner;
+                            
+              class Test {
+                  String s = Joiner.on(", ").join(new String[] {"a"});
+              }
+              """,
+            """                            
+              class Test {
+                  String s = String.join(", ", new String[] {"a"});
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void joinIterables() {
+        //language=java
+        rewriteRun(
+          java(
+            """
+              import com.google.common.base.Joiner;
+              import java.util.Set;
+                            
+              class Test {
+                  String s = Joiner.on(", ").join(Set.of("a"));
+              }
+              """,
+            """                            
+              import java.util.Set;
+
+              class Test {
+                  String s = String.join(", ", Set.of("a"));
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void joinMixedCharSequences() {
+        //language=java
+        rewriteRun(
+          java(
+            """
+              import com.google.common.base.Joiner;
+                            
+              class Test {
+                  String s = Joiner.on(", ").join("a", new StringBuilder("b"));
+              }
+              """,
+            """                    
+             class Test {
+                 String s = String.join(", ", "a", new StringBuilder("b"));
+             }
+              """
+          )
+        );
+    }
+
+    @Test
+    void joinEmptyIterables() {
+        //language=java
+        rewriteRun(
+          java(
+            """
+              import com.google.common.base.Joiner;
+              import java.util.HashSet;
+                            
+              class Test {
+                  String s = Joiner.on(", ").join(new HashSet<String>());
+              }
+              """,
+            """                            
+              import java.util.HashSet;
+
+              class Test {
+                  String s = String.join(", ", new HashSet<String>());
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void joinMethodOnSeparateLine() {
+        //language=java
+        rewriteRun(
+          java(
+            """
+              import com.google.common.base.Joiner;
+                            
+              class Test {
+                  String s = Joiner.on(", ")
+                                   .join("a", "b");
+              }
+              """,
+            """                            
+              class Test {
+                  String s = String.join(", ", "a", "b");
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void dontEditJoinersNotSupportedByString() {
+        //language=java
+        rewriteRun(
+          java(
+            """
+              import com.google.common.base.Joiner;
+              import java.util.Set;
+                            
+              class Test {
+                  String s1 = Joiner.on(", ").join("a", 1);
+                  String s2 = Joiner.on(", ").skipNulls().join("a", "b");
+                  String s3 = Joiner.on(", ").useForNull("null").join("a", "b");
+                  String s4 = Joiner.on(", ").join(Set.of("a").iterator());
+                  //String s5 = Joiner.on(',').join("a");
+              }
+              """
+          )
+        );
+    }
+
+    @Test
+    void dontEditJoinerInstanceCaller() {
+        //language=java
+        rewriteRun(
+          java(
+            """
+              import com.google.common.base.Joiner;
+                            
+              class Test {
+                  Joiner j = Joiner.on(", ");
+                  String s1 = j.join("a", "b");
+              }
+              """
+          )
+        );
+    }
+
+}