KTIJ-19680 'Replace with a for loop' and backward conversion could work for 'forEachIndexed'

[t-kameyama]

https://youtrack.jetbrains.com/issue/KTIJ-19680 https://youtrack.jetbrains.com/issue/KTIJ-19679

[comitative]

Thank you for your contribution!

It seems that the current implementation is not yet fully correct and needs some more work as well as additional unit tests. Here are some examples there the intention provides wrong results.

1. If the for loop has no braces, the loop body is lost after the conversion to forEachIndexed.

for ((index, element) in withIndex()) println("$index : $element")

results in

forEachIndexed { index, element ->
}

2. If the forEachIndexed call is an expression body of a function, the quick fix currently produces the syntactically incorrect result.

fun List<Int>.foo() = forEachIndexed { index, element -> println("$index : $element") }

is replaced by

fun List<Int>.foo() = for ((index, element) in withIndex()) {
    println("$index : $element")
}

The same problem occurs with the forEach call.

I think that the simplest solution is to check if the forEach/'forEachIndexed` call is an expression body, and do not generate the "Replace with a 'for' loop" action for expression bodies.

Another option would be to implicitly convert the expression body to a block body (by reusing an existing quick fix) and then to convert the function call to a for loop, but I think it would be more difficult to implement and may be less clear to users.

3. You did a good job to convert continue to return@forEachIndexed and vice versa, but the break statement is not supported.

For example, let's look at this sample.

fun test() {
    for ((index, element) in listOf(1, 2, 3).withIndex()) {
        println("$index: $element")
        if (index == 1) break
    }
}

An incorrect code is generated during the conversion, as the break statement is not allowed outside the for loop.

fun test() {
    listOf(1, 2, 3).forEachIndexed { index, element ->
        println("$index: $element")
        if (index == 1) break
    }
}

[t-kameyama]

Fixed, please take another look.

1. If the for loop has no braces, the loop body is lost after the conversion to forEachIndexed.

7d580831829c3f57d7c3b1e017cb13ec458ee0ff

2. If the forEachIndexed call is an expression body of a function, the quick fix currently produces the syntactically incorrect result.

b162a37aed8171cd68bc9313513a94c972be39bc

3. You did a good job to convert continue to return@forEachIndexed and vice versa, but the break statement is not supported.

0364a925946b6ce6794e1793439b293271e012db

[t-kameyama]

I'll resolve conflicts.

[t-kameyama]

I'll resolve conflicts.

Done

[t-kameyama]

Created a new PR for KTIJ-19679.

[t-kameyama]

Created a new PR for KTIJ-19680.