[Bug] Issues with CtClass::compileAndReplaceSnippets compiling method call after comment

[lapplislazuli]

Hi there,

I came accross an weird issue.
I wanted to add an empty method to a class, as well as a simple method call in another method.

Expected Output

From:

class A {
    public int mult(int a, int b){
         return a * b;
    }
}

To:

class A {
    public int mult(int a, int b){
         // New Comment
         otherMethod();
         return a * b;
    }
   
   private void otherMethod(){

   }
}

Actual Output

after first compileAndReplaceSnippets:

class A {
    public int mult(int a, int b){
         // New Comment
         return a * b;
         return a * b;
    }
   
   private void otherMethod(){

   }
}

after second compileAndReplaceSnippets, it throws an error for unreachable code (which seems reasonable).

Code to reproduce

    @Tag("Regression")
    @Test
    void testSnippetReplacement_ReplaceMethodCallSnippetAfterComment_shouldNotThrowError(){
        String initialClass = "package some; class A { public int mult(int a, int b){return a * b;}";

        CtClass<?> containingClass = Launcher.parseClass(initialClass);
        String methodName = "vanishingMethodCall";

        var methodToAlter= containingClass.getMethodsByName("mult").get(0);

        // Build an empty method, return void
        CtMethod emptyMethod = containingClass.getFactory().createMethod();
        emptyMethod.setSimpleName(methodName);
        emptyMethod.setParent(containingClass);
        emptyMethod.setType(emptyMethod.getFactory().Type().VOID_PRIMITIVE);
        emptyMethod.addModifier(ModifierKind.PRIVATE);
        emptyMethod.setBody(emptyMethod.getFactory().createBlock());

        containingClass.addMethod(emptyMethod);

        containingClass.compileAndReplaceSnippets();

        methodToAlter.getBody().addStatement(0,
                containingClass.getFactory().createCodeSnippetStatement(methodName+"()"));

        methodToAlter.getBody().addStatement(0,containingClass.getFactory().createInlineComment("I seem to break the test"));

        // This creates the double return
        containingClass.compileAndReplaceSnippets();
        // This fails the test, as the second return does not compile
        containingClass.compileAndReplaceSnippets();

        return;
    }

Further Info / Considerations

This only occurs when there is a comment before the method. If you remove the line where the InlineComment is added, the test succeeds.

It also duplicates longer statements, such as if-blocks. it seems to duplicate any statement after the comment.

Other

I am using Spoon-Core 8.3.0, in a maven project. Spoon is only used as a library.

As a workaround, at the moment I'll try to not call the method with a snippet.

[lapplislazuli]

Short addendum:

This behaviour occurrs apparently on all comment types not only on inline comments.

Also I'd be happy if you could give me a small pointer how to properly build the method invocation :)

[MartinWitt]

´The error is inside SnippetCompilationHelper#compileAndReplaceSnippetsIn CtPath#evaluateOn returns an empty List and we use iterator.next(); on it [link]. Ignoring empty lists does not fix the problem.

spoon/src/main/java/spoon/support/compiler/SnippetCompilationHelper.java

Line 85 in 1de9318

elements2after.put(p, p.evaluateOn(f.getModel().getRootPackage()).iterator().next());