What version of OpenRewrite are you using?

• rewrite-static-analysis: 2.34.1
• rewrite-core: 8.81.13
• rewrite-java: 8.81.13

What is the smallest, simplest way to reproduce the problem?

• Related to UseLambdaForFunctionalInterface produces invalid diamond-operator cast when converting anonymous class using diamond with new #892 (another case where UseLambdaForFunctionalInterface does not account for the declaration context before converting), but a different code path: UseLambdaForFunctionalInterface produces invalid diamond-operator cast when converting anonymous class using diamond with new #892 is about diamond operators in method-argument casts, this is about local variable assignments with var.

class Main {
  interface Action {
    String run(String input);
  }

  void execute() {
    final var action =
        new Action() {
          @Override
          public String run(String input) {
            return input.toUpperCase();
          }
        };
    action.run("hello");
  }
}

Run org.openrewrite.staticanalysis.UseLambdaForFunctionalInterface.

What did you expect to see?

Either no change, or the recipe should replace var with the explicit interface type (Action) when performing the conversion.

var can hold a functional interface only when the right-hand side provides an explicit target type, such as new Action() { ... }. A lambda expression is not a standalone expression and requires its target type to come from the declaration. With var, that target type is absent (JLS 14.4.1, 15.27.1).

What did you see instead?

The recipe converts the anonymous class to a lambda while keeping var:

void execute() {
    final var action =
            input -> input.toUpperCase();
    action.run("hello");
}

The rewritten code no longer compiles:

error: cannot infer type for local variable action
    final var action =
              ^

What is the full stack trace of any errors you encountered?

Downstream compilation fails with:

CampaignStoreImplTest.java:1472: error: cannot infer type for local variable campaignUpdate
    final var campaignUpdate =
              ^
CampaignStoreImplTest.java:1510: error: cannot infer type for local variable stateUpdate
    final var stateUpdate =
              ^
CampaignStoreImplTest.java:1512: error: cannot infer type for local variable livePeriodUpdate
    final var livePeriodUpdate =
              ^