descriptor: Formal ABNF for digest values

[wking]

I'm not sure what the grammar language was before, but this commit converts it to ABNF and references the defining RFC.

The ABNF highlighting comes from here and here.

[AkihiroSuda]

I prefer current notation over ABNF for readability, although little a bit informal

[wking]

On Tue, Apr 25, 2017 at 10:01:53AM -0700, Akihiro Suda wrote: I prefer current notation over ABNF for readability, although little a bit informal

Enforcing a MUST based on informal notation seems like more trouble than reading the ABNF ;). And while the current syntax is more compact, the ABNF RFC is about the size of the BRE spec [1] and it makes it easy to compose a more complicated rule from simpler rules, while BREs do not. The current syntax may be Go's syntax [2], but that looks underspecified to me unless you say “as implemented in Go 1.8” or some such. [1]: http://pubs.opengroup.org/onlinepubs/9699919799/ [2]: https://golang.org/pkg/regexp/syntax/

[stevvooe]

@wking Could you please stop filing PRs that invalidate others? Please submit an issue and discuss the change before submitting.

[stevvooe]

Enforcing a MUST based on informal notation seems like more trouble
than reading the ABNF ;).

Also, there is nothing informal about the syntax here. Regular expressions are well-defined and understood by a broader group of readers than ABNF.

[vbatts]

this seems to be coming from left field and not needed. closing.

[wking]

Also, there is nothing informal about the syntax here. Regular expressions are well-defined…

The syntax grammar is informal because the current grammar language is undefined. If we wanted to formally use a known regex language (for example), we'd need to link to the spec defining it.

[erikh]

https://en.m.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions ?

…

On Mon, May 1, 2017 at 12:31 PM W. Trevor King ***@***.***> wrote: Also, there is nothing informal about the syntax here. Regular expressions are well-defined… The syntax grammar is informal because the current grammar language is undefined. If we wanted to formally usie a known regex language (for example), we'd need to link to the spec defining it. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#655 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AABJ6_ftFpkSZSiqdAEU-YXEQHyQbVvjks5r1jMPgaJpZM4NHvsX> .

[wking]

On Mon, May 01, 2017 at 01:04:12PM -0700, Erik Hollensbe wrote: https://en.m.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions ?

I'm fine linking [1] as an alternative to this PR, but with just BREs you'd need to have a single regexp for the whole digest. To decompose it into parts (e.g. an algorithm and a hex/encoded part), you'd need to use ABNF or some other syntax for defining concatenation. But as it stands, the spec links nothing to define the syntax being used. [1]: http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_03