Tslint: [no-conditional-assignment]

[felipeochoa]

Feature request

I'd like to request the feature discussed in the original implementation of the no-conditional-assignment rule.

The code I'm cleaning up has the following:

let varName: SomeType | null;
while (varName = maybeNullExpensiveCalculation()) {
  // Do stuff with varName, requiring that it not be null
}

It would be great to be able to just add another set of parens around the assignment, which I think is more or less standard, to avoid having to add a tslint annotation.

Another alternative here is to make it into a while (true) loop with a check and break at the top, but that's a little ugly:

while (true) {
  const varName = maybeNullExpensiveCalculation();
  if (varName === null) break;
  // Do stuff with varName, requiring that it not be null
}

[giladgray]

@felipeochoa there's always a third option: disable the rule for the line, making it clear that this assignment is intentional.

let varName: SomeType | null;
// tslint:disable-next-line:no-conditional-assignment
while (varName = maybeNullExpensiveCalculation()) {
  // Do stuff with varName, requiring that it not be null
}

[felipeochoa]

Oh yes. Forgot to mention that somehow!

[karfau]

Is your featuer request that the rule no-conditional-assignment should not show an error when writing the following code:

let varName: SomeType | null;
while ((varName = maybeNullExpensiveCalculation())) {
  // Do stuff with varName, requiring that it not be null
}

?

I would not like such exception since it is not obvious for me how this is different from the code you posted.

[felipeochoa]

The surrounding parentheses are a common convention to tell the linter that you're assigning on purpose

[JoshuaKGoldberg]

common convention

@felipeochoa can you provide references for that?

[felipeochoa]

GCC has the -Wparentheses option which behaves in this way. (See e.g., this comment)

ESLint defaults to this style (except-parens) for their no-cond-assign rule.

Python assignment expressions are usually required to be enclosed in parens for readability

Etc.

[JoshuaKGoldberg]

SGTM. Let's take in an option to allow this the way ESLint does.

[armpogart]

The same applies also fore RegExp assignment in conditionals, such as:
while ((match = someRegExp.exec("string")) { .... }
or
while ((match = someRegExp.exec("string") !== null) { .... }
I see clear condition here and don't think that it's right to mark as a potential problem.

[karfau]

I think both oft these examples are missing one closing paren.

And all the time I'm asking myself: the additional parents are not making a technical difference in the resulting value, right?
So if those are not a problem in your code base, why don't you just disable the rule (on the next-line, file or on the global level...)?
But I the question might be beyond the scope of this feature request.

[adidahiya]

Closing due to low priority and the deprecation roadmap #4534

[JoshuaKGoldberg]

🤖 Beep boop! 👉 TSLint is deprecated 👈 _(#4534)_ and you should switch to typescript-eslint! 🤖

🔒 This issue is being locked to prevent further unnecessary discussions. Thank you! 👋