[RFC 0045] Deprecating unquoted URL syntax (NixOS#45)

* A small RFC on deprecating URL syntax

* Convert alternatives to a list

* Add a mention of tooling in future work

* A remark from @globin about one more problem with unquoted URLs

* Grammar edit: comparison of URLs, paths and strings.

Co-Authored-By: 7c6f434c <7c6f434c@mail.ru>

* Style edit: possibility of future removal

Co-Authored-By: 7c6f434c <7c6f434c@mail.ru>

* 0045: commit to using the tooling that now exists

* Update rfcs/0045-deprecate-url-syntax.md

Shepherd team

Co-Authored-By: Domen Kožar <domen@enlambda.com>

* Fix shepherd list

* Update based on a discussion

* Explicitly make future removal conditional on editions; restrict the claim about no special support to the Nix language itself

rfcs/0045-deprecate-url-syntax.md

@@ -0,0 +1,69 @@
+---
+feature: deprecate_url_syntax
+start-date: 2019-04-28
+author: Michael Raskin
+co-authors: 
+shepherd-leader: Eelco Dolstra
+shepherd-team: Eelco Dolstra, zimbatm, Silvan Mosberger
+related-issues: 
+---
+
+# Summary
+[summary]: #summary
+
+Discourage and eventually remove the use of unquoted URL syntax in Nix code and especially
+Nixpkgs.
+
+# Motivation
+[motivation]: #motivation
+
+The Nix language has a special syntax for URLs even though quoted strings can also be used to represent them. Unlike paths, URLs do not
+have any special properties in the Nix expression language
+that would make the difference useful.
+Moreover, using
+variable expansion in URLs requires some URLs to be quoted strings anyway. So
+the most consistent approach is to always use quoted strings to represent URLs.
+Additionally, a semicolon immediately after the URL can be mistaken for a part
+of URL by language-agnostic tools such as terminal emulators.
+
+Tools
+targeting only Nixpkgs codebase can ignore URL syntax once Nixpkgs phases out
+its use.
+
+# Detailed design
+[design]: #detailed-design
+
+Add a note in the Nix manual that the special unquoted URL syntax is
+discouraged and may be removed in a future edition of the Nix language.
+
+Add a note in the Nixpkgs manual that the unquoted URL syntax should not be used anymore.
+
+Convert all the unquoted URLs in the Nixpkgs codebase to quoted strings.
+
+Add an ofBorg check that verifies that no new unquoted URLs have been added in
+a PR.
+
+# Drawbacks
+[drawbacks]: #drawbacks
+
+This is a minor cosmetic issue (and maybe a very minor readability issue) which
+might not be worth making a specific decision.
+
+# Alternatives
+[alternatives]: #alternatives
+
+* Do nothing; get PRs from time to time that make homepages uniformly quoted
+  strings or uniformly unquoted.
+
+* Decide to use unquoted URLs for all URLs without special characters or
+  variable expansion.
+
+# Unresolved questions
+[unresolved]: #unresolved-questions
+
+Currently none.
+
+# Future work
+[future]: #future-work
+
+Currently none.