[RFC 0035] Default name from pname

rfcs/0035-default-name-from-pname.md

@@ -0,0 +1,137 @@
+---
+feature: default_name_from_pname
+start-date: 2018-10-02
+author: Patrick Hilhorst (@Synthetica9)
+co-authors: (find a buddy later to help our with the RFC)
+related-issues:
+  - https://github.com/NixOS/nixpkgs/pull/41627
+  - https://github.com/NixOS/nixpkgs/pull/49398
+---
+
+# Summary
+[summary]: #summary
+
+Whenever the `version` and `pname` attribute are both present, use
+`"${pname}-${version}"` as the default value for `name` for `mkDerivation`.
+
+# Motivation
+[motivation]: #motivation
+
+The string `"${pname}-${version}"` appears verbatim in the nixpkgs repo [627
+times](appendixA), at the time of this writing. Variants of this string appear
+[746 times][appendixA], with the most common variant being `baseName`. This RFC
+would reduce repetition in nixpkgs, and would allow for the `rec` keyword to be
+removed from an unknown number of places.
+
+This RFC was originally submitted as [nixpkgs PR #41627][originalPR]. This PR
+received some positive attention:
+
+![Positive attention on the original PR][Upvotes]
+
+However, it was [suggested][useRFC] by @edolstra that this should go through the
+RFC process instead of directly implementing it in nixpkgs.
+
+# Detailed design
+[design]: #detailed-design
+
+The basic design is simple: change the default value for the `name` attribute of
+`mkDerivation` to `"${pname}-${version}"` if both attributes are present
+(implemented in [`c313e07`][basicChange])
+
+Care should be taken to assure that position information is transferred
+correctly (implemented in [`0c1d5d1`][positionInfo]) and to add an assertion
+that the generated name is consistent with the actual name if all three
+attributes are present (implemented in [`e0d2348`][checkConsistent]). Because
+some packages already define a prefix to their `pname`-`version` pair (for
+example: `python2.7-setuptools-40.2.0`), it might be better to use
+`lib.strings.hasSuffix` here instead of `(==)`.
+
+`git cherry-pick`-ing these three commits (keeping the mentioned caveats in
+mind) should be sufficient to get this RFC implemented. It is discouraged to
+continue on the original PR, since a lot of it has gone out of date since.
+
+# Drawbacks
+[drawbacks]: #drawbacks
+
+  * It could confuse users unfamiliar with this RFC where a package gets its
+    name from.
+  * It makes a currently unofficial (but not discouraged) practice official,
+    and enshrines the `pname` attribute name into "law". Once this RFC is
+    implemented, there is no easy way of changing this attribute name again.
+    _Note: `pname` is already used for Python packages, but in this context,
+    `name = "${python.libPrefix}-${pname}-${version}"`.
+
+# Alternatives
+[alternatives]: #alternatives
+
+Other than doing nothing, there doesn't seem to be an alternative design.
+
+# Unresolved questions
+[unresolved]: #unresolved-questions
+
+* Is `pname` the correct attribute name to use for this? Or should we go with
+  the (~7.5×) less common, but more descriptive `baseName`?
+
+# Future work
+[future]: #future-work
+
+Future PR's that use the old pattern of `"${pname}-{version}"` (or a variant
+thereof) should be requested to change to use the new pattern suggested here.
+
+There could be a gradual cleanup of old code, to make sure all derivations use
+this new pattern.
+
+# Appendix A: Occurances of Variants
+[appendixA]: #appendix-A
+
+```sh     
+$ ag --nix '"\$\{\w+\}-\$\{version\}"' --no-filename --only-matching | sort | uniq --count | sort --numeric-sort
+      1 "${appname}-${version}"
+      1 "${appName}-${version}"
+      1 "${attr}-${version}"
+      1 "${cmd}-${version}"
+      1 "${drvName}-${version}"
+      1 "${flavor}-${version}"
+      1 "${fullName}-${version}"
+      1 "${nameMajor}-${version}"
+      1 "${name_}-${version}"
+      1 "${package_name}-${version}"
+      1 "${packageName}-${version}"
+      1 "${pkgName}-${version}"
+      1 "${plainName}-${version}"
+      1 "${pName}-${version}"
+      1 "${prefix}-${version}"
+      1 "${shortName}-${version}"
+      1 "${simpleName}-${version}"
+      1 "${srcName}-${version}"
+      1 "${stname}-${version}"
+      1 "${toolName}-${version}"
+      2 "${artifactId}-${version}"
+      2 "${pkg}-${version}"
+      2 "${p_name}-${version}"
+      2 "${shortname}-${version}"
+      3 "${basename}-${version}"
+      3 "${libname}-${version}"
+      3 "${_name}-${version}"
+      3 "${package}-${version}"
+      3 "${program}-${version}"
+      4 "${project}-${version}"
+      5 "${pkgname}-${version}"
+      5 "${product}-${version}"
+      7 "${gemName}-${version}"
+      9 "${repo}-${version}"
+     24 "${name}-${version}"
+     85 "${baseName}-${version}"
+    627 "${pname}-${version}"
+    746
+```
+
+<!-- Links used in the RFC: -->
+
+[originalPR]:      https://github.com/NixOS/nixpkgs/pull/41627
+[upvotes]:         https://i.imgur.com/vosd6YG.png
+[useRFC]:          https://github.com/NixOS/nixpkgs/pull/41627#issuecomment-395750781
+
+[basicChange]:     https://github.com/NixOS/nixpkgs/pull/41627/commits/c313e07
+[positionInfo]:    https://github.com/NixOS/nixpkgs/pull/41627/commits/0c1d5d1
+[checkConsistent]: https://github.com/NixOS/nixpkgs/pull/41627/commits/e0d2348