Add Upcase ident in Macro

[recrack]

This feature is for rust-css colors.
see : servo/rust-css#22

something like:

define_color!(aliceblue, 240, 248, 255);

which would expand to:

static ALICEBLUE: Color = Color { red: 240, green: 248, blue: 255, alpha: 1.0 };

when is use upcaseident!(aliceblue), it can become ALICEBLUE(uppercase).

ex))

let AA = "hi"
assert!(upcase_indent!(aa)== AA);

[graydon]

Huh. I'm not so sure about this one. Synthesizing or modifying identifiers between source code and compiled form, in general, goes against the grep test (http://jamie-wong.com/2013/07/12/grep-test/) which I generally think of as worth trying to pass. Why not just pass the actual identifier ALICEBLUE into the macro?

[metajack]

It kind of sucks if you have to write define_color!(ALICEBLUE, "aliceblue"); There are a few hundred of these, and we'd have to write every color name twice just to define them. We could make all the statics lowercase, but that isn't idiomatic.

Then there is the other part of it which is macro-izing the giant match statement to parse color names. We were hoping to do parse_color!(some_str, aliceblue, antiquewhite, ...); instead of parse_color!(some_str, ALICEBLUE, "aliceblue", ANTIQUEWHITE, "antiquewhite", ...);`.

Is there another way around this such that we don't have to repeat the same characters multiple times?

[metajack]

Obviously one way around it is to write a Python script that parses a simple text file and generates the Rust code, but I was hoping to leverage the macro system instead.

[brson]

If this is something that requires procedural macros but isn't appropriate for rustc maybe we could namespace it in a way that is obvious that it's not for general use, until dynamically loadable syntax extensions work, then remove it from rustc.

[brson]

Or maybe we could add some macros with other support functionality such that this could be written as a macro-by-example.

[graydon]

Oh, I didn't realize the string name repeated it. That's .. More ok? I just thought I'd raise the concern, generally synthetic idents are a bit of an anti feature. Not a hard r-, if it's really needed.

[metajack]

Sorry, I slightly misspoke here. The parse_color! macro could just switch to using uppercase. But the match statement needs a string and an ident of the same name.

I suppose we could pass the grep test if we instead downcased the ident to make the string. But it would involve a very similar function to this one to turn ALICEBLUE into aliceblue and then we'd put it in quotes.

[graydon]

Maybe a variant on stringify then, yeah?

[kud1ing]

I have written SVG parsers in the past and it appears to me that defining HTML color names is a one-off job which can be automated (in my case using copy/paste and search/replace).

Beyond rust-css where do we see this being used?

[pnkfelix]

I think we should just close this pull request. The conversation between graydon and metajack shows a path towards a alternate (if similar) solution for color names that does not break the grep test: namely, a variant on stringify that downcases. (Unless someone comes up with a real-world use case that cannot be re-encoded in a reasonable way given that hypothetical stringify_downcase! macro.)

[brson]

Closing per @pnkfelix