enhancement: Add quiet flag to hide warnings

[MatthewHerbst]

Sometimes you may want to run linting but ignore any warnings produced, such as in a CI environment where you only want lint failures to fail the build (many runners will check both the exit code and STDERR to see if the program has passed).

This mimics the quiet flag available in ESLint, which hides errors from output when passed.

PR checklist

• Addresses an existing issue: #0000
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of change:

Adds a new CLI flag, quiet, to allow hiding of lint warnings.

Is there anything you'd like reviewers to focus on?

What's the best way to test this? I've been having trouble trying to do it in the linterTests. I've been trying:

const withWarningDeclaration =
`
  console.log("This line will not pass linting with the default rule set");
`;

it("shows warnings", () => {
    const config = DEFAULT_CONFIG;
    config.rules.set("no-console", {
        ruleArguments: ["log"],
        ruleName: "no-console",
        ruleSeverity: "warning",
    });
    
    const linter = new TestLinter({ fix: false });
    const fileToLint = createTempFile("ts");
    fs.writeFileSync(fileToLint, withWarningDeclaration);
    linter.lint(fileToLint, "Don't Need This If We Have A Program", config);
    const result = linter.getResult();

    assert.equal(result.warningCount, 1);
    assert.equal(result.errorCount, 0);
});

describe("when the `quiet` flag is passed", () => {
    ...
    it("does not show warnings", () => {
        ...
    });
});

But that doesn't seem to produce any warnings or errors. Any idea why?

CHANGELOG.md entry:

enhancement: added quiet flag to allow hiding of lint warnings

[palantirtech]

Thanks for your interest in palantir/tslint, @MatthewHerbst! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[MatthewHerbst]

@johnwiseheart (pinging you since I've seen you active on a few other PRs recently): any chance I could please get any feedback on this? Thank you!

[johnwiseheart]

Going to look into your testing issue, and will get back to you.

[johnwiseheart]

Can you use a new variable here rather than overwriting this.failures - perhaps something like:

const errors = this.failures.filter((failure) => failure.getRuleSeverity() === "error");
const failures = this.options.quiet ? errors : this.failures;

[MatthewHerbst]

Sure, done!

[johnwiseheart]

@MatthewHerbst with regard to your test:

it("shows warnings", () => {
    const config = DEFAULT_CONFIG;
    config.rules.set("no-console", {
        ruleArguments: ["log"],
        ruleName: "no-console",
        ruleSeverity: "warning",
    });

    const linter = new TestLinter({ fix: false });  // <---- You're not passing in a program
    const fileToLint = createTempFile("ts");
    fs.writeFileSync(fileToLint, withWarningDeclaration);
    linter.lint(fileToLint, withWarningDeclaration, config); // <-- So when you call lint you need to pass the file contents
    const result = linter.getResult();

    assert.equal(result.warningCount, 1);
    assert.equal(result.errorCount, 0);
});

After passing in the contents of the file, your code works for me. That said, I'm not 100% confident that I'm right since my TSLint knowledge is fairly basic. Please correct me if I'm wrong.

[johnwiseheart]

Also, please rebase on top of master to fix the tests

[MatthewHerbst]

Ah, I see, I messed up thinking about the Program was, thank you! Will fix it now

[MatthewHerbst]

@johnwiseheart any other changes you'd like to see on this? Thanks again for the reviews!

[johnwiseheart]

Looks good to me! Thanks for your contribution!