tsc with no comment flags remove some comments.

[mxtopher]

TypeScript Version: 2.1.5

Code

class Promise {
    then(callback:any){};
};

function commentedPromise(){
    new Promise()
    /* Commented Promise */.then(function(){});
}

function commentedParameters(
/* Parameter a */
a
/* End of parameter a */
/* Parameter b */
,
b
/* End of parameter b */
){}

Expected behavior:

This should be the compiled version:

var Promise = (function () {
    function Promise() {
    }
    Promise.prototype.then = function (callback) { };
    ;
    return Promise;
}());
;
function commentedPromise() {
    new Promise()
        /* Commented Promise */.then(function () { });
}
function commentedParameters(
/* Parameter a */
a
/* End of parameter a */
/* Parameter b */
,
b
/* End of parameter b */
) { }

Actual behavior:

This is what I get

var Promise = (function () {
    function Promise() {
    }
    Promise.prototype.then = function (callback) { };
    ;
    return Promise;
}());
;
function commentedPromise() {
    new Promise()
        .then(function () { });
}
function commentedParameters(
    /* Parameter a */
    a, b) { }

I agree these comments are in very weird positions, but I have a custom build system which uses /#IFDEF/ style guards, and I'm migrating a codebase with some hundreds of them.

Typescript is stripping some of these comments without warning.

[mxtopher]

A comment in the last line of an if block which precedes an else block is also removed:

function ifelse() {
    if(commentedParameters(1,2)){
        /*comment1*/
        commentedParameters(3,4);
        /*comment2*/
    }else{
        commentedParameters(5,6);
    }
}

Comment2 is removed when compiled.

[nickzelei]

Posting this here for freshness

TypeScript also appears to be removing comments in this fashion:
ts:
const foo: boolean = var1 || /* istanbul ignore next */ null;

js:
var foo = var1 || null;

This is painful when trying to get code coverage and are setting ignore statements.

[grovesNL]

I believe this one is also relevant (TypeScript Playground):

TypeScript:

const a = {
    b: 1, // Invisible comment
    c: 1 // Visible comment
};

JavaScript:

var a = {
    b: 1,
    c: 1 // Visible comment
};

[yuit]

@Zelein after investigating the issue, your example is different than original issue and would require much larger change to our code, mainly how leading comments (current we use linefeed to differentiate between leading comments of current node and trailing comment of previous node) are computed and possible our tree structure. To unblock your scenario, I would suggest do the following instead.

const foo: boolean = false || 
    /* istanbul ignore next */ null;

@grovesNL it is similar on your case as well. Because "," isn't store in AST, we can't get the trailing comment from "previous node" but the comment is also not a leading comment of the next node.

Please feel free to open a separate issue on your comment. Thanks!