Tslint: no-unused-variable: shouldn't warn about all params in some cases

[chrismbarr]

Bug Report

• TSLint version: 3.11.0
• TypeScript version: 1.8.10
• Running TSLint via: gulp-tslint via Visual Studio 2015
  

  TypeScript code being linted

this.$scope.$on("$myEvent", (event: angular.IAngularEvent, customerNumber: string) => {
    this.getCustomerInfo(customerNumber);
});

with tslint.json configuration:

"no-unused-variable": [ true, "check-parameters" ],

Actual behavior

The event parameter is reported as unused, which _is technically correct_... but it has to be there so I can access the 2nd parameter, which I need.

Right now I'm needing to put comments like // tslint:disable-next-line:no-unused-variable all over the place.

Expected behavior

Since I only need to use the 2nd parameter, it seems dumb to warn me about the first parameter not being used since this is how the framework I'm using works.

[jkillian]

You can use the "ignore-pattern" option in this case to specify a regex that corresponds to variables that are intentionally unused. For example,

"no-unused-variable": [true, {"ignore-pattern": "^_"}]

would ignore all variables that start with an underscore and not report errors when they are unused.

Going to close this issue because "ignore-pattern" is designed exactly for this scenario!

[chrismbarr]

so I'd have to go through my code and rename variables based on their parameter order just to satisfy this rule?

[jkillian]

Yep, but it's not that unusual: starting unused variables with an underscore is a standard convention in languages with stricter compilers, like Go and Rust, as far as I know.

[chrismbarr]

So if I were to rename that first var to _event and later on it was used by someone who was not aware of this convention, would that be flagged?

[jkillian]

Good question - I believe the rule only works one way here. TSLint won't complain if you use a variable that meets the "ignore-pattern" option

[chrismbarr]

Perhaps that could be a configurable option to add to this rule?

[marcoturi]

to me it is a bug, tslint should not throw error in this case.

[adidahiya]

@marcoturi no-unused-variable is deprecated in favor of compiler options and we plan to remove it in the next major version, see #1481. I filed #1851 to address the sparse documentation around this.