Highlighting Javascript Inline Block Comments in Vim

Question

Background

I use JScript (Microsoft's ECMAScript implementation) for a lot of Windows system administration needs. This means I use a lot of ActiveX (Automated COM) objects. The methods of these objects often expect Number or Boolean arguments. For example:

var fso = new ActiveXObject("Scripting.FileSystemObject");
var a = fso.CreateTextFile("c:\\testfile.txt", true);
a.WriteLine("This is a test.");
a.Close();

(CreateTextFile Method on MSDN)

On the second line you see that the second argument is one that I'm talking about. A Boolean of "true" doesn't really describe how the method's behavior will change. This isn't a problem for me, but my automation-shy coworkers are easily spooked. Not knowing what an argument does spooks them. Unfortunately a long list of constants (not real constants, of course, since current JScript versions don't support them) will also spook them. So I've taken to documenting some of these basic function calls with inline block comments. The second line in the above example would be written as such:

var a = fso.CreateTextFile("c:\\testfile.txt", /*overwrite*/ true, /*unicode*/ false);

That ends up with a small syntax highlighting dilemma for me, though. I like my comments highlighted vibrantly; both block and line comments. These tiny inline block comments mean little to me, personally, however. I'd like to highlight those particular comments in a more muted fashion (light gray on white, for example). Which brings me to my dilemma.

Dilemma

I'd like to override the default syntax highlighting for block comments when both the beginning and end marks are on the same line. Ideally this is done solely in my vimrc file, and not in a superseding personal copy of the javascript.vim syntax. My initial attempt is pathetic:

hi inlineComment    guifg=#bbbbbb
match inlineComment "\/\*.*\*\/"

Straight away you can see the first problem with this regular expression pattern is that it's a greedy search. It's going to match from the first "/*" to the last "*/" on the line, meaning everything between two inline block comments will get this highlight style as well. I can fix that, but I'm really not sure how to deal with my second concern.

Comments can't be defined inside of String literals in ECMAScript. So this syntax highlighting will override String highlighting as well. I've never had a problem with this in system administration scripts, but it does often bite me when I'm examining the source of many javascript libraries intended for browsers (less.js for example).

What regex pattern, syntax definition, or other solution would the amazing StackOverflow community recommend to restore my vimrc zen?

Answer 1

I'm not sure, but from your description it sounds like you don't need a new syntax definition. Vim syntax files usually let you override a particular syntax item with your own choice of highlighting. In this case, the item you want is called javaScriptComment, so a command like this will set its highlighting:-

hi javaScriptComment guifg=#bbbbbb

but you have to do this in your .vimrc file (or somewhere that's sourced from there), so it's evaluated before the syntax file. The syntax file uses the highlight default command, so the syntax file's choice of highlighting only affects syntax items with no highlighting set. See :help :hi-default for more details on that. BTW, it only works on Vim 5.8 and later.

The above command will change all inline /* */ comments, and leave // line comments with their default setting, because line comments are a different syntax item (javaScriptLineComment). You can find the names of all these groups by looking at the javascript.vim file. (The easiest way to do this is :e $VIMRUNTIME/syntax/javascript.vim .)

If you only want to change some inline comments, it's a little more complicated, but still easy to see what to do by looking at javascript.vim . If you do that, you can see that block comments are defined like this:-

syn region javaScriptComment start="/\*" end="\*/" contains=@Spell,javaScriptCommentTodo

See that you can use separate regexes for begin and end markers: you don't need to worry about matching the stuff in between with non-greedy quantifiers, or anything like that. To have a syntax item that works similarly but only on one line, try adding the oneline option (:h :syn-oneline for more details):-

syn region myOnelineComment start="/\*" end="\*/" oneline

I've removed the two contains groups because (1) if you're only using it for parameter names, you probably don't want spell-checking turned on inside these comments, and (2) contained sections that aren't oneline override the oneline in the container region, so you would still match all TODO comments with this region.

You can define this new kind of comment region in your .vimrc, and set the highlighting how you like: it looks like you already know how to do that, so I won't go into more details on that. I haven't tried out this particular example, so you may still need a bit of fiddling to make it work. Give it a try and let me know how it goes.

Answer 2

Why don't you simply add a comment line above the call?

I think that

// fso.CreateTextFile(filename:String, overwrite:Boolean, unicode:Boolean)
var a = fso.CreateTextFile("c:\\testfile.txt", true, false);

is a lot more readable and informative than

var a = fso.CreateTextFile("c:\\testfile.txt", /*overwrite*/ true, /*unicode*/ false);