Beautify mode: comments are lost in the end of function body

[thorn0]

For example,

function f() {
  /* comment1 */
  alert(1);
  /* comment2 */
}

becomes

function f() {
  /* comment1 */
  alert(1);
}

[mishoo]

There are other cases too. Generally, comments are lost if there is no AST node following them on the current nesting level. More examples:

if (foo /* lost comment */ && bar /* lost comment */) {
    // this one is kept
    bar();
    /* lost comment */
}

// comments right before EOF are lost as well

It's a known problem and I kept thinking of it but there's no easy fix.

[Francisc]

Hello,

It seems comments are also lost when code follows as opposed to closing curly brace in your example:

/*! a */
var someVar=1;
/*! someArray */
var someArray=[];
/*! someObject */
var someObject={};
var blabla;

[getify]

Another troublesome example of this problem is with dropped function names:

(function/*!foo*/a(){ console.log(a); })();

=>

!function/*!foo*/o(){console.log(o)}();

But:

(function/*!foo*/a(){ console.log("uh oh"); })();

=>

!function(){console.log("uh oh"))}();

Note: I think my particular example of this comment-dropping is related to #547 in that I think going forward we're going to need an option for not dropping function expression names (even if they're not lexically referenced) -- just filed #552 for such.

BUT, it would certainly be nice if /*!foo*/ could be preserved even in:

(function/*!foo*/(){ console.log(a); })();

=>

!function(){console.log(a)}();

[gaborbernat]

Any solution for this? :)

[xtianjohns]

While I'm not certain that the causes are related, I've found another case where comments will not be preserved. Apologies if there is a duplicate issue: closest potential I found was #478.

With comments: /@foo/, the following will not produce any comments:

// example one

if ( true ) { console.log( true ); }
// @foo bar
if ( true ) { console.log( true ); }

// example two

if ( true ) { console.log( true ); }
// @foo bar
if ( true ) { console.log( true ); }
var x;

// example three

if ( true ) { console.log( true ); }
// @foo bar
if ( true ) { console.log( true ); }
anything();

However, this configuration will produce a comment:

if ( true ) { console.log( true ); }
// @foo bar
var x;

Someone should be able to reproduce with version 2.5.0, and with default options. Example:

require( 'uglify-js' ).minify( 'foo.js', {
  output: {
    comments: /@foo/,
  },
});

Important note: I can get this behavior with a regular expression and the 'license' comments option. @avdg may have alluded to why that might be, but even passing 'all' or true does not seem to alter the behavior in my examples.

[kzc]

Certain AST transformations will cause comments to be lost. If you selectively disable some compress options your example will work.

uglifyjs your_code.js --bare-returns --comments all -m -c "sequences=false, dead_code=false"

but comments in the following code will not be preserved with these options:

foo(1 + /* hello */ 2 /* world */ + 3);

===>

foo(6);

Some optimizations are destructive and leave no place for comments. I suppose they could be collected and put at the end of the transformed expression but it would look odd.

[avdg]

I wonder if AST_Scope can contain the comments at the end of a block. This will need to be investigated technically to see if this can be implemented...

[avdg]

(please note that this doesn't mean that I will work on it. I'll be probably too busy to implement this for now)

[tyomo4ka]

Just to confirm that the issue is still there in version 2.6.4.

[avdg]

Tracking as https://github.com/avdg/UglifyJS2/projects/3#card-250044

[avdg]

👍