Make three font-lock faces customizable

[vemv]

Introduce clojure-global-constant-face, clojure-def-symbol-face, clojure-lambda-arg-face.

Updated tests, although I couldn't get to run them (never had done so. Tried with M-x ert):

Selector: t
Passed:  0
Failed:  0
Skipped: 0
Total:   0/0

Started at:   2018-01-01 07:14:57+0100
Finished.
Finished at:  2018-01-01 07:14:57+0100

[bbatsov]

Two notes from me:

• This overlaps with No special font-locking for mixedCase, CamelCase #462 which suggest dropping constant font-locking for everything but those 3 symbols
• I don't think that the term for them is really global constants, although I'm not sure what is it, technically speaking

[vemv]

• Broadened the scope of this PR to span a couple more deffaces I needed
• Can rename to boolean-or-nil, sounds good?
• Regarding No special font-locking for mixedCase, CamelCase #462, it doesn't seem all that related (although I can wait for it to be merged; would avoid obvious merge conflict). In that PR, two deffaces still exist. I think the more deffaces the better, else syntactically unrelated tokens get a coupled coloring.

IOW, clojure-mode currently decides that def and cond must get the same coloring, which can be frustrating. The more this is parameterized the better?

(I could open a PR introducing 12 deffaces... but better to go on an as-needed basis)

[bbatsov]

Regarding #462, it doesn't seem all that related (although I can wait for it to be merged; would avoid obvious merge conflict).

That certainly seems related to me. :-)

[bbatsov]

I'm don't like this idea. There's nothing special about definitions that warrants a different face for them.

[bbatsov]

I don't understand why they can't be font-locked as variables, as this is what they are. That seems like an odd decision to me. And I don't think we use the variable face for anything but them.

[bbatsov]

else syntactically unrelated tokens get a coupled coloring.

But what you're suggesting goes against the spirit of what your saying - we don't care about definitions, we care about macros, special forms, etc. I can imagine someone wanted to be able to differentiate a special form form a macro, but Emacs modes have traditionally avoided this, so I just followed suit here. Having different faces for the same syntactic category (e.g. defn and cond) seems both confusing and excessive.

I general I'm ok to add some extra faces for things that are not part of the standard Emacs font-locking, but I'm not ok with adding faces for subjective reasons.

[vemv]

Hi there, thanks for sharing your reasoning!

but Emacs modes have traditionally avoided this, so I just followed suit here

Fair enough, although it also can be frustrating to be limited by design decisions made maybe decades ago.

font-lock presumes that all languages' syntaxes can be mapped 1-1 to each other, e.g. all languages have "constants" (therefore font-lock-constant-face exists).

That's a noble goal to seek, and probably it's good enough 95% of the times. But eventually someone will want finer-grained control for his favorite language.

---

Maybe if I explain my exact use case you'll see it better. Corrections welcome.

• I like core macros / special forms with a distinct coloring -plain yellow-, helps me see the flow of my code
• I like foo (in def foo) to be prominently colored -darker yellow-, so all those names are skimmable in a given ns:

It's great that those names are in a distinct, stronger color from anything else. That way my eyes can easily find the def I'm looking for.

• But: def is a special form, and foo (from def foo) is intended to be prominent. See what happens without my patch applied:

The names aren't prominent anymore. So, the symbols def/defn should be as plain as possible, like in my previous screenshot. But I cannot do that without affecting cond, if etc.

---

I general I'm ok to add some extra faces for things that are not part of the standard Emacs font-locking, but I'm not ok with adding faces for subjective reasons.

I hope I gave a good-enough rationale! In any case, we can make the docstrings advocate the "normal" thing:

- "Face used to font-lock the Clojure global constants: nil, true, false."
+ "Face used to font-lock the Clojure global constants: nil, true, false. Note that you should normally configure font-lock-constant-face instead"

WDYT?

Cheers - Victor

[bbatsov]

Seems to me a part of your problem is some odd decision in your color-theme to use very similar colors for special forms and function names. In mine this looks like this:

WDYT?

I'll ruminate on the subject.

[vemv]

Rumination appreciated!

I see the point of your screenshot, it's nice but if you look at the third defn, there's no contrast between defn and the case below it, resulting in the top-level looking "chunky".

Generally I strive to keep things visually separated: def from <name>, declaration "headers" from body, and so on. That way I can parse things more quickly.

[vemv]

Updated PR to solve merge conflicts.

Could you give a think to the pending disagreement?

[bbatsov]

I completely forgot about this. The first face doesn't really make sense anymore as we dropped the notion of special face for interop forms. We also dropped the notion of a special face for SNAKE_CASE constants, I guess having a special face for 3 constants is pointless now.

And I still don't think that definitions warrant a special face, so I'm inclined to just reject this suggestion. @clojure-emacs/cider any thoughts from anyone else?

[vemv]

I completely forgot about this.

No issue, thanks for the reply!

I was thinking, while my goal is somewhat reasonable (namely: to color Clojure as I deem semantic), the needs of 1 developer shouldn't impact the clojure-mode codebase.

Perhaps a cleaner solution would be to separate the relevant .el parts to a different .el file, so I can cleanly, fine-grainedly replace it (instead of maintaining a personal clojure-mode fork, as I do right now).

So basically you'd have the same code as today, but split into more files.

[bbatsov]

Well, you can always replicate the approach of https://github.com/clojure-emacs/clojure-mode/blob/master/clojure-mode-extra-font-locking.el

This is some font-locking that used to live in clojure-mode, but I deemed it too unreliable and removed it, but I still provided it as a package in case someone really liked it.