The description at Running Rewrite without build tool plugins suggests that OpenRewrite can be run on any Java project without requiring that project being a Maven or Gradle project. However, I could not manage to get the described class RunRewriteManually to compile properly.
When building "as is" I get
.../src/main/java/com/wamas/core/rewrite/Rewrite.java:49: error: incompatible types: Stream<SourceFile> cannot be converted to List<CompilationUnit>
List<J.CompilationUnit> cus = javaParser.parse(sourcePaths, projectDir, ctx);
^
.../src/main/java/com/wamas/core/rewrite/Rewrite.java:53: error: incompatible types: List<CompilationUnit> cannot be converted to LargeSourceSet
List<Result> results = recipe.run(cus, ctx).getResults();
^
Adding .collect(Collectors.toList() to the first statement doesn't improve it because the types don't match:
/src/main/java/com/wamas/core/rewrite/Rewrite.java:50: error: incompatible types: inference variable T has incompatible bounds
List<J.CompilationUnit> cus = javaParser.parse(sourcePaths, projectDir, ctx).collect(Collectors.toList());
^
equality constraints: CompilationUnit
lower bounds: SourceFile
where T is a type-variable:
T extends Object declared in method <T>toList()
This second case is more a Java than an OpenRewrite problem, but I just don't get the error cause.