Emacs: rainbow-identifiers, customized

From Amit’s Thoughts

A few months ago I had read Evan Brook's post about using text editor colors for identifiers instead of keywords. I tried the two Emacs modes for this: rainbow-identifiers and color-identifiers-mode. I wrote up my thoughts back then, and that blog post led to some features being added to rainbow-identifiers. Pros and cons:

Neither is a clear win. Try both and see. I ended up using rainbow-identifiers. However, there were too many identifiers being colored, which meant there were too many colors, which meant I couldn't really distinguish things anymore. Here's what color-identifiers looks like:

var edges = this.graph.edges_from(this.curr);
for (var i = 0; i < edges.length; i++) {
    var next = edges[i];
    var edge_weight = this.graph.edge_weight(this.curr, next);
    if (edge_weight != Infinity) {
        this.neighbors.push(next);
        mark_changed(next);
        if (!this.visited[next]) {
            this.g[next] = this.g[this.curr] + edge_weight;
            this.open.push(next);
            this.parent[next] = this.curr;
            this.visited[next] = true;
        }
    }
}

And here's what rainbow-identifiers looks like:

var edges = this.graph.edges_from(this.curr);
for (var i = 0; i < edges.length; i++) {
    var next = edges[i];
    var edge_weight = this.graph.edge_weight(this.curr, next);
    if (edge_weight != Infinity) {
        this.neighbors.push(next);
        mark_changed(next);
        if (!this.visited[next]) {
            this.g[next] = this.g[this.curr] + edge_weight;
            this.open.push(next);
            this.parent[next] = this.curr;
            this.visited[next] = true;
        }
    }
}

You can see that color-identifiers picks out local variables and not all names. And rainbow-identifiers colors lots of things, but it misses the variable declaration, which is important to color. So I configured rainbow-identifiers to do this:

var edges = this.graph.edges_from(this.curr);
for (var i = 0; i < edges.length; i++) {
    var next = edges[i];
    var edge_weight = this.graph.edge_weight(this.curr, next);
    if (edge_weight != Infinity) {
        this.neighbors.push(next);
        mark_changed(next);
        if (!this.visited[next]) {
            this.g[next] = this.g[this.curr] + edge_weight;
            this.open.push(next);
            this.parent[next] = this.curr;
            this.visited[next] = true;
        }
    }
}

It's in between the default configuration of the two packages. I highlight declarations in bold, and in color. I highlight local variables. I highlight local fields (this.x). But I don't highlight all names. Here's my configuration:

;; Customized filter: don't mark *all* identifiers
(defun amitp/rainbow-identifiers-filter (beg end)
  "Only highlight standalone words or those following 'this.' or 'self.'"
  (let ((curr-char (char-after beg))
        (prev-char (char-before beg))
        (prev-self (buffer-substring-no-properties
                    (max (point-min) (- beg 5)) beg)))
    (and (not (member curr-char 
                    '(?0 ?1 ?2 ?3 ?4 ?5 ?6 ?7 ?8 ?9 ??)))
         (or (not (equal prev-char ?\.))
             (equal prev-self "self.")
             (equal prev-self "this.")))))

;; Filter: don't mark identifiers inside comments or strings
(setq rainbow-identifiers-faces-to-override
      '(font-lock-type-face
        font-lock-variable-name-face
        font-lock-function-name-face))

;; Set the filter
(add-hook 'rainbow-identifiers-filter-functions 'amitp/rainbow-identifiers-filter)

;; Use a wider set of colors
(setq rainbow-identifiers-choose-face-function
      'rainbow-identifiers-cie-l*a*b*-choose-face)
(setq rainbow-identifiers-cie-l*a*b*-lightness 45)
(setq rainbow-identifiers-cie-l*a*b*-saturation 45))

I also turned off colors for the font-lock faces, and made font-lock-variable-name-face bold. I still think it may be too many colors, so I may end up turning off rainbow-identifiers and trying some of the things Wilfred Hughes has suggested.

Labels: emacs, howto