A practitioner’s primer on deterministic software modernization

// Supply code snippet
// The consumer's identify
personal String identify = "Java";

// LST illustration
J.VariableDeclarations | "// The consumer's namenprivate String identify = "Java""
|---J.Modifier | "personal"
|---J.Identifier | "String"
---J.VariableDeclarations.NamedVariable | "identify = "Java""
    |---J.Identifier | "identify"
    ---J.Literal | ""Java""

Recipes work with many various file varieties together with XML or YAML to switch issues like Maven POMs or different configuration information. In addition they can create new information when wanted as a part of migrations. However recipes don’t even have to switch code in any respect. A strong characteristic and good thing about the wealthy knowledge from the LST is that they could simply collect knowledge and insights, analyzing code bases to generate knowledge tables for use for studies, metrics, or visualizations that assist groups perceive their code earlier than making adjustments.

Testing recipes: Deterministic and dependable

OpenRewrite’s deterministic nature makes recipes simple to check. Right here’s how easy it’s to visualise the adjustments a recipe ought to make, and to confirm it really works appropriately:

@Check
void migrateJUnitTest() {
    rewriteRun(
        // The recipe to check
        new MigrateToJUnit5(),
        
        // Earlier than: JUnit 4 code
        java("""
            import org.junit.Check;
            
            public class MyTest {
                @Check
                public void testSomething() {}
            }
            """),
            
        // After: Anticipated JUnit 5 outcome
        java("""
            import org.junit.jupiter.api.Check;
            
            public class MyTest {
                @Check
                public void testSomething() {}
            }
            """)
    );
}

This check framework validates that the recipe produces precisely the anticipated output—no extra, no much less. As a result of recipes are deterministic, the identical enter all the time produces the identical outcome, making them dependable and testable at scale.