How to make a rule that disables implicit truthy conversion from function to boolean

[ziriax]

We have a large typescript application, and sometimes we have code like

if (shouldFireNuclearMissiles)...

while we should have written

if (shouldFireNuclearMissiles())...

(pun intended).

So forgetting to evaluate a function results in a truthy value.

Is it possible to write a rule that forbids this kind of implicit function-to-boolean conversions?

Or does this require forking typescript?

Thanks,
Peter

[HamletDRC]

This would be quite a nice rule.

A couple things to consider:

• tslint analyzes one file at a time and does not look at imports or /// <ref imports. This means that if "shouldFireNuclearMissiles" is defined in some other file then tslint will consider it an 'any' type. This means that, for the most part, tslint will have no idea what type your function is
• tslint does not have a reliable type checker. Even if "shouldFireNuclearMissles" is a locally defined function, tslint will see it as an 'any' type. Again, this means the rule will not work that well.

We could make this rule, but honestly it would miss about 95% of the violations. That isn't much safety.

[ziriax]

Thanks for the fast reply!

I forked and modified the Typescript compiler for checking this. I was amazed how cleanly it was written, so it was very easy to hack, it took less than 2 hours!.

And indeed, we found some bugs in our large code base :-)

But I'm pretty sure the Typescript team will not want this kind of checks, as they deviate too much from Javascript?

Personally I hate automatic truthy and falsy conversions in large projects, the comfort they bring does not outweigh the dangers.

[joshbw]

I don’t think it would hurt to submit the idea on the TS project and see what they think. Personally I’d love to see this as part of a TSStrictMode option where the devs could tell the compiler to be much more pedantic about potential issues

From: Peter Verswyvelen [mailto:[email protected]]
Sent: Tuesday, April 19, 2016 6:42 AM
To: Microsoft/tslint-microsoft-contrib [email protected]
Subject: Re: [Microsoft/tslint-microsoft-contrib] How to make a rule that disables implicit truthy conversion from function to boolean (#112)

Thanks for the fast reply!

I forked and modified the Typescript compiler for checking this. I was amazed how cleanly it was written, so it was very easy to hack, it took less than 2 hours!.

And indeed, we found some bugs in our large code base :-)

But I'm pretty sure the Typescript team will not want this kind of checks, as they deviate too much from Javascript?

Personally I hate automatic truthy and falsy conversions in large projects, the comfort they bring does not outweigh the dangers.

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Reply to this email directly or view it on GitHubhttps://github.com//issues/112#issuecomment-211927477

[myitcv]

This is covered in palantir/tslint#253

[ziriax]

Great!

However, the feedback I got from @HamletDRC seems to indicate that in most cases this is useless since the node type will be infered to be any instead of boolean, for the reasons he described?

[reversi-fun]

@ziriax and @joshbw ,Hang in there.

Implementation of that new Tsllint rule not easy than hack of tsc-complier.

(a) TSLint use TSC-Complier with "compilerOptions.noResolve = true".
SO function'S type seems "Any" or "undefined" by TSLint-rules.
(b) TSC-Compiler read only one sourceFile at 1 TSLint-Roule, not read any other SourceFile sutch as function defined in.

for (a); I have been challenged to workaround, performance has become very bad.
Issues:[ScopedSymbolTrackingWalker.typeChecker returns undefinedhttps://github.com//issues/94]

for (b);TSLint-Contributors says that No-Good "search" for the many file, and tsconfig.json read in TSLint-task, to be compiles.

I hope that the better solution is created.
I'm Sorry for My broken English.

[HamletDRC]

I am closing this issue here because it will be part of TSLint when they start linting entire programs as a whole.