Make CollectorMutability an error

The ten Collectors.toList() calls are now Stream.toList(), as CLAUDE.md
asks of new code, and StringWrapper's Collectors.toMap is
toUnmodifiableMap. Nothing changed any of these collections after they
were built, and none holds a null, so only their mutability differs:
the lists go to command lines, records and assertions, and the map is
only read. The previous commit's test round-trips the IntelliJ
settings' classpath, the one list that goes through a serializer.

Author: abashev

build.gradle

@@ -83,6 +83,7 @@ subprojects {
     // Java toolchains, javac and test settings; Error Prone. Both in buildSrc/src/main/groovy.
     apply plugin: 'open-java-format.java-conventions'
     apply plugin: 'open-java-format.error-prone-conventions'
+    apply plugin: 'open-java-format.forbidden-apis-conventions'
 
     dependencies {
         // Gives a version to the JUnit artifacts that useJUnitJupiter() adds without one.

buildSrc/build.gradle

@@ -13,5 +13,6 @@ repositories {
 dependencies {
     implementation 'net.ltgt.gradle:gradle-errorprone-plugin:5.1.1'
     implementation 'net.ltgt.gradle:gradle-nullaway-plugin:3.3.0'
+    implementation 'de.thetaphi:forbiddenapis:3.11'
     implementation 'org.jreleaser:org.jreleaser.gradle.plugin:1.26.0'
 }

buildSrc/src/main/groovy/open-java-format.error-prone-conventions.gradle

@@ -26,6 +26,7 @@ tasks.withType(JavaCompile).configureEach {
             handleTestAssertionLibraries = true
         }
         error('CanonicalAnnotationSyntax')
+        error('CollectorMutability')
         error('DirectReturn')
         error('FormatStringConcatenation')
         error('JUnitClassModifiers')

buildSrc/src/main/groovy/open-java-format.forbidden-apis-conventions.gradle

@@ -0,0 +1,14 @@
+// Bans Guava's immutable collections in favour of java.util ones; the list is config/forbidden-apis.
+plugins {
+    id 'java'
+    id 'de.thetaphi.forbiddenapis'
+}
+
+forbiddenApis {
+    signaturesFiles = files(rootProject.file('config/forbidden-apis/guava-immutables.txt'))
+    ignoreFailures = true
+}
+
+tasks.withType(de.thetaphi.forbiddenapis.gradle.CheckForbiddenApis).configureEach {
+    ignoreFailures = true
+}

config/forbidden-apis/guava-immutables.txt

@@ -0,0 +1,4 @@
+@defaultMessage Use java.util collections: List.of, List.copyOf, Map.of, Stream.toList()
+com.google.common.collect.ImmutableList
+com.google.common.collect.ImmutableMap
+com.google.common.collect.ImmutableSet

gradle-open-java-format/src/test/java/com/palantir/javaformat/gradle/FormatDiffTest.java

@@ -34,7 +34,6 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.concurrent.TimeUnit;
-import java.util.stream.Collectors;
 import java.util.stream.Stream;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
@@ -58,7 +57,7 @@ void parsing_git_diff_output_works() throws IOException {
 
         List<String> strings = FormatDiff.parseGitDiffOutput(example1)
                 .map(FormatDiff.SingleFileDiff::toString)
-                .collect(Collectors.toList());
+                .toList();
         assertThat(strings)
                 .containsExactly(
                         "SingleFileDiff{path=build.gradle, lineRanges=[[24..25), [29..30)]}",
@@ -121,7 +120,7 @@ private static List<Path> getClasspath() throws IOException {
                 .omitEmptyStrings()
                 .splitToStream(Files.readString(CLASSPATH_FILE.toPath()))
                 .map(Path::of)
-                .collect(Collectors.toList());
+                .toList();
     }
 
     private static Path javaBinPath() {

open-java-format-idea-plugin/src/main/java/com/palantir/javaformat/intellij/FormatterProvider.java

@@ -36,7 +36,6 @@
 import java.util.NoSuchElementException;
 import java.util.Optional;
 import java.util.function.Supplier;
-import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import static java.util.Optional.ofNullable;
@@ -92,7 +91,7 @@ private static Optional<FormatterService> createFormatter(FormatterCacheKey cach
     }
 
     private static List<Path> getProvidedImplementationUrls(List<URI> implementationClasspath) {
-        return implementationClasspath.stream().map(Path::of).collect(Collectors.toList());
+        return implementationClasspath.stream().map(Path::of).toList();
     }
 
     private static List<Path> getBundledImplementationUrls() {
@@ -127,7 +126,7 @@ private static List<Path> getImplementationUrls(
 
     private static List<Path> listDirAsUrlsUnchecked(Path dir) {
         try (Stream<Path> list = Files.list(dir)) {
-            return list.collect(Collectors.toList());
+            return list.toList();
         } catch (IOException e) {
             throw new UncheckedIOException("Couldn't list dir: " + dir, e);
         }

open-java-format-idea-plugin/src/main/java/com/palantir/javaformat/intellij/PalantirJavaFormatSettings.java

@@ -32,7 +32,6 @@
 import java.util.List;
 import java.util.Optional;
 import java.util.jar.JarFile;
-import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import static java.util.Optional.ofNullable;
@@ -158,13 +157,13 @@ static class StoredSettings {
 
         public void setImplementationClassPath(@Nullable List<String> value) {
             implementationClassPath = Optional.ofNullable(value)
-                    .map(strings -> strings.stream().map(URI::create).collect(Collectors.toList()));
+                    .map(strings -> strings.stream().map(URI::create).toList());
         }
 
         @Nullable
         public List<String> getImplementationClassPath() {
             return implementationClassPath
-                    .map(paths -> paths.stream().map(URI::toString).collect(Collectors.toList()))
+                    .map(paths -> paths.stream().map(URI::toString).toList())
                     .orElse(null);
         }
 

open-java-format-jdk-bootstrap/src/main/java/com/palantir/javaformat/bootstrap/BootstrappingFormatterService.java

@@ -84,7 +84,7 @@ private ImmutableList<Replacement> getFormatReplacementsInternal(String input, C
                 jvmArgsForVersion(jdkMajorVersion),
                 implementationClassPath,
                 /* outputReplacements= */ true,
-                ranges.stream().map(RangeUtils::toStringRange).collect(Collectors.toList()));
+                ranges.stream().map(RangeUtils::toStringRange).toList());
 
         Optional<String> output =
                 FormatterCommandRunner.runWithStdin(command.toArgs(), input, Optional.ofNullable(jdkPath.getParent()));

open-java-format-jdk-bootstrap/src/main/java/com/palantir/javaformat/bootstrap/NativeImageFormatterService.java

@@ -31,7 +31,6 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Optional;
-import java.util.stream.Collectors;
 
 public class NativeImageFormatterService implements FormatterService {
     private static final ObjectMapper MAPPER =
@@ -49,7 +48,7 @@ public ImmutableList<Replacement> getFormatReplacements(String input, Collection
             FormatterNativeImageArgs command = new FormatterNativeImageArgs(
                     nativeImagePath,
                     /* outputReplacements= */ true,
-                    ranges.stream().map(RangeUtils::toStringRange).collect(Collectors.toList()));
+                    ranges.stream().map(RangeUtils::toStringRange).toList());
 
             output = FormatterCommandRunner.runWithStdin(
                     command.toArgs(), input, Optional.ofNullable(nativeImagePath.getParent()));