Allow trailing lines in multiline comment directives

[JoshuaKGoldberg]

TypeScript Version: 4.0.0-dev.20200507

Search Terms: multiline comment directive ts-expect-error ts-ignore

Code

const x = 0;

/* @ts-ignore
continuing comment 
 that could be multiline*/

x();

Expected behavior:

The comment looks like a directive to ignore the x();'s type checking complaint.

Actual behavior:

Comment directive parsing only looks at the last line of the comment. It should also allow the first line of the comment.

I'm in favor of not allowing any other lines (i.e. "middle" lines) to count as directives. Extending to allow characters after the @ts- has precedent from what's already allowed (we're really just adding newlines). But putting characters before the @ts- has a precedent of not working even in single-line comments.

/* Here we use a
@ts-ignore
 that is multiline*/

Playground Link: https://www.typescriptlang.org/play/?ssl=1&ssc=1&pln=28&pc=2#code/MYewdgzgLgBAHjAvDADAbgFAYPQCoYACUEAtAJYDmYIATgKYahhRlgCurFMoAtj3cxgYYUABYBDWKDYAbACYwARnRg9ZLGazq5sWOAAoAlGiA

Related Issues: Following discussion in #38228 (comment), as suggested by @sheetalkamat.

[sheetalkamat]

@DanielRosenwasser and @RyanCavanaugh should comment on whether @ts-ignore is allowed anywhere in the comment or not but the scenario particularly shows discrepancies is:

    // @ts-ignore
    // come comment
    // some other comment

    // @another

    x(); // This ignores error 

    /* @ts-ignore */
    /*another comment
     that could be multiline*/

    x(); // while this does not ignore error

    /* @ts-ignore */
    // another comment
     // that could be multiline

    x(); // this will ignore the error

    // @ts-ignore
    /*another comment
     that could be multiline*/

    x(); // while this does not ignore error

[DanielRosenwasser]

Wow,

    // @ts-ignore
    // come comment
    // some other comment

    // @another

    x(); // This ignores error 

Really!?

[sheetalkamat]

@DanielRosenwasser we have test for that which i only realized when i was looking into #38296 and e860d48 failed for the test

[RyanCavanaugh]

@DanielRosenwasser Oof. Please come up with some kind of specification on how this should work