Extracting lambda expression - without {} - to a new method creates valid java code

[Honza-cz]

resolves #6311

Fixes the issue linked to extracting parameterized lambda into a method. I tested manually all cases I have in mind. The fix itself is not nicest, but it works. I was unable to write meaningful automated tests for that class.

source code:

public class ExtractMethodDemo11 {
    
    public static void main(String[] args) {
        String unused = "unused";
        String first = "hello";
        String second = "world";

        System.out.println(
                java.util.Optional.ofNullable("-")
                        .map(t -> first + t + second)
                        .orElseThrow()
        );
    }
}

extracting first + t + second:

public class ExtractMethodDemo11 {
    
    public static void main(String[] args) {
        String unused = "unused";
        String first = "hello";
        String second = "world";

        System.out.println(java.util.Optional.ofNullable("-")
                        .map(t -> inner(first, t, second))
                        .orElseThrow()
        );
    }

    private static String inner(String first, String t, String second) {
        return first + t + second;
    }
}

extracting t -> first + t + second:

public class ExtractMethodDemo11 {
   
    public static void main(String[] args) {
        String unused = "unused";
        String first = "hello";
        String second = "world";

        System.out.println(java.util.Optional.ofNullable("-")
                        .map(inner(first, second))
                        .orElseThrow()
        );
    }

    private static Function<String, String> inner(String first, String second) {
        return t -> first + t + second;
    }
}

As I mentioned in bug, lambda with {} still cannot be extracted correctly to a method. The problem is with return type of the newly created method which is taken not from lambda, but from enclosing method. I was not able to resolve this issue yet.

[sdedic]

Question: if PHASE_INSIDE_SELECTION is active, then the node is already added in scan() line 106 ?

[Honza-cz]

Yes, scan method is called before visit* methods

[sdedic]

I'd use == here.

[Honza-cz]

ok

[sdedic]

hmmm ... what about nested lambdas ? Suppose a code like

Runnable r = () -> new Worker() { 
   public void n() {
     doSomething(variable);
   }
   public void someOverrideMethod() {
      someExecutor.execute(
// selection starts here
       () -> whateverMethodCall(variable);
// selection ends here
      );
   }
}.run();

The lambda flag becomes true on the outermost lambda, which is still unrelated to the selection

[Honza-cz]

I was checking this use case with nested lambda. It is true, that flag is set for whole lambda. On the other hand it seems to fix the issue. I realized a new occurrence of issue, tested on netbeans 19:

static void dummy(final String first) {
    String unused = "unused";
    String second = "world";

    Runnable r = () -> {
        Runnable g = () -> {
            final String m = first + second + m1;
            System.out.println("m" + m);
        };
    };
}

select first + second + m1 => extract => non compilable code:

static void dummy(final String first) {
    String unused = "unused";
    String second = "world";

    Runnable r = () -> {
        Runnable g = () -> {
            final String m = aaa();
            System.out.println("m" + m);
        };
    };
}

private static String aaa() {
    return first + second + m1;
}

with my version it create valid code:

static void dummy(final String first) {
    String unused = "unused";
    String second = "world";

    Runnable r = () -> {
        Runnable g = () -> {
            final String m = aaa(first, second);
            System.out.println("m" + m);
        };
    };
}

private static String aaa(final String first, String second) {
    return first + second + m1;
}

I was testing nested lambada and it works fine, just some a sample:

public static void main(String[] args) {
    String unused = "unused";
    String first = "hello";
    String second = "world";

    Function<String,Integer> f1 = t -> {
        Function<String,String> f2 = u -> {
            final String m = first + second + m1;
            System.out.println("m" + m);

            final Function<String, Integer> len = s -> (u + s + m + first + m1).length();
            System.out.println("len" + len.apply("hello"));

            return (u + m + first + m1);
        };

        return f2.apply(t).length();

    };

}

=> various extract to method:

public static void main(String[] args) {
    String unused = "unused";
    String first = "hello";
    String second = "world";

    Function<String, Integer> f1 = t -> {
        Function<String, String> f2 = u -> {
            final String m = z1(first, second);
            System.out.println("m" + m);

            Function<String, Integer> len = z3(u, m, first);
            System.out.println("len" + len.apply("hello"));

            return (u + m + first + m1);
        };

        return z4(f2, t);

    };

}

private static int z4(Function<String, String> f2, String t) {
    return f2.apply(t).length();
}

private static Function<String, Integer> z3(String u, final String m, String first) {
    final Function<String, Integer> len = s -> z2(u, s, m, first);
    return len;
}

private static int z2(String u, String s, final String m, String first) {
    return (u + s + m + first + m1).length();
}

private static String z1(String first, String second) {
    return first + second + m1;
}

What didn't work if I select whole statement with return return f2.apply(t).length(); but this is another issue which I was not able to fix yet (and announced it in the description above)

I admit that isLambda flag is a bit magic flag, but it works in case of lambda or non-lambda code. At least I was not able to find a use case, which could be broken by this flag.

Do you want me to dig deeper?

[mbien]

hi @Honza-cz
could you add a test case analog to:

netbeans/java/java.hints/test/unit/src/org/netbeans/modules/java/hints/introduce/IntroduceHintTest.java

Lines 1092 to 1124 in dc529e6

	public void testIntroduceMethod179258() throws Exception {
	performFixTest("package test;\n" +
	"public class Test {\n" +
	" public static void test() {\n" +
	" String test = null;\n" +
	" |test = \"foo\";\n" +
	" if (test == null) {\n" +
	" System.err.println(1);\n" +
	" } else {\n" +
	" System.err.println(2);\n" +
	" }|\n" +
	" }\n" +
	"}",
	("package test;\n" +
	"public class Test {\n" +
	" public static void test() {\n" +
	" String test = null;\n" +
	" name();\n" +
	" }\n" +
	" private static void name() {\n" +
	" String test;\n" +
	" test = \"foo\";\n" +
	" if (test == null) {\n" +
	" System.err.println(1);\n" +
	" } else {\n" +
	" System.err.println(2);\n" +
	" }\n" +
	" }\n" +
	"}")
	.replaceAll("[ \t\n]+", " "),
	new DialogDisplayerImpl3("name", EnumSet
	.of(Modifier.PRIVATE), true));
	}

| marks start/end of the selection which is supposed to be extracted.

regarding paperwork:

• please make sure the commit has your full name as author, you can check it by looking at the patch file of the PR: https://github.com/apache/netbeans/pull/6595.patch
• please squash everything to one commit and rebase it on latest master once ready to merge