Recipe to transform uses of Collections.unmodifiableXX to Immutable Static Factory Methods

[yeikel]

I believe that this belongs here (otherwise please let me know under what module this should be reported)

it would be nice to add a rule to the Java 8 -> Java 11 migration to apply the following transformation :

Before :

Set<String> s = Collections.unmodifiableSet(new HashSet<>(Arrays.asList("A", "B")));

After

Set<String> s = Set.of("A", "B")

Additional resources :

See : https://docs.oracle.com/en/java/javase/11/core/creating-immutable-lists-sets-and-maps.html#GUID-930A5334-9413-4E87-A1D7-6FF4E9E421B2

[yeikel]

Another similar transformation :

final List<String> elements = Collections.unmodifiableList(Arrays.asList("A","B"));
final List<String> elements = List.of("A","B"));

[yeikel]

Another example :

Map<String,String> elements = new HashMap<>();
elements.put("hello","world");
Map<String, String> s = Collections.unmodifiableMap(elements);

Map<String, String> s = Map.of("hello", "world");

[tkvangorder]

@yeikel This is a very good suggestion.

[traceyyoshima]

@yeikel I added the base recipes for the examples you provided in this commit.

I decided not to handle situations like:

Before

List<String> stringList = Arrays.asList("a", "b", "c");
stringList = Collections.unmodifiableList(stringList);

After

List<String> stringList = List.of("a", "b", "c");

Because it would require removing a statement and there could be relevant code in between lines 1 and 2, a multi-variable declaration, etc.

Dataflow analysis is in development and we'll be able to handle the transformation safely once it's finished.

Thanks again for the suggestion!

[yeikel]

@yeikel I added the base recipes for the examples you provided in this commit.

I decided not to handle situations like:

Before

List<String> stringList = Arrays.asList("a", "b", "c");
stringList = Collections.unmodifiableList(stringList);

After

List<String> stringList = List.of("a", "b", "c");

Because it would require removing a statement and there could be relevant code in between lines 1 and 2, a multi-variable declaration, etc.

Dataflow analysis is in development and we'll be able to handle the transformation safely once it's finished.

Thanks again for the suggestion!

Thar makes sense. Thank you for explaining!

[yeikel]

@traceyyoshima

While testing my changes for #80

I found that the following condition is not covered by your implementation (basically any custom type)

@Issue("https://github.com/openrewrite/rewrite-migrate-java/issues/67")
@Test
    fun unmodifiableSetTyped() = assertChanged(
        before = """
            import java.util.*;
            import java.time.LocalDate;

            class Test {
                Set<Integer> s = Collections.unmodifiableSet(new HashSet<>(Arrays.asList(LocalDate.of(2010,1,1),LocalDate.now())));
            }
        """,
        after = """
            import java.util.Set;
            import java.time.chrono.ChronoLocalDate;

            class Test {
                Set<LocalDate> s = Set.of(LocalDate.of(2010,1,1),LocalDate.now());
            }
        """
    )

I tried fixing it myself, but I am not sure how the MethodMatcher should look like in this case

[traceyyoshima]

@yeikel thanks for letting me know. I'll take a look first thing on Monday :)

[yeikel]

@traceyyoshima Did you get a chance to take a look at this? I noticed it was released today without the fix :(

[traceyyoshima]

Hi @yeikel!

Apologies, not yet. I'm working on a few things related to the release and haven't had time yet.

But I know what the issue is:

• The method arguments in the template need to be updated from #{} to #{any()} to allow types.
• The test needs to be updated from Set<Integer> to Set<LocalDate>.

[traceyyoshima]

@yeikel just pushed the update. Thanks again!

[yeikel]

@yeikel just pushed the update. Thanks again!

Thank you!