[bug#48667] [PATCH] doc: Expound on how to specify the version of a package.

[Xinglu Chen <public@yoctocell.xyz>]

* doc/guix.texi (package Reference): Describe how packages that lack a release
or are pinned to an unreleased version should specify the ‘version’ field.
Add documentation for the ‘git-version’ procedure.
---
I am unsure if the format for packages that don’t have a release should
be ‘0.0.0-REVISION.COMMIT’ or just ‘0-REVISION.COMMIT’.

 doc/guix.texi | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index e8b0485f78..083f65c9c5 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -89,6 +89,7 @@ Copyright @copyright{} 2020 Jonathan Brielmaier@*
 Copyright @copyright{} 2020 Edgar Vincent@*
 Copyright @copyright{} 2021 Maxime Devos@*
 Copyright @copyright{} 2021 B. Wilson@*
+Copyright @copyright{} 2021 Xinglu Chen@*
 
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3 or
@@ -6651,7 +6652,18 @@ This is the data type representing a package recipe.
 The name of the package, as a string.
 
 @item @code{version}
-The version of the package, as a string.
+The version of the package, as a string.  If there are no releases of
+the package, or a unreleased version is desired, the version should
+contain @code{VERSION-REVISION.COMMIT}.  @code{VERSION} is
+@c TODO: 0.0.0 or just 0 ?
+@code{0.0.0} or whatever the latest version is, and @code{REVISION} is
+the revision of the Guix package (@code{0} if it is a new package),
+whenever the package is updated to a newer version the revision should
+also be bumped.  @code{COMMIT} is the @dfn{commit} or @dfn{changeset}
+corresponding to the version, it should only contain 7 characters.  If
+the fetch method is @code{git-fetch} (@pxref{origin Reference}), there
+is the @code{git-version} procedure that makes it easier to specify the
+version.
 
 @item @code{source}
 An object telling how the source code for the package should be
@@ -6757,6 +6769,15 @@ automatically corrected.
 @end table
 @end deftp
 
+@deffn {Scheme Procedure} git-version @var{VERSION} @var{REVISION} @var{COMMIT}
+Return the version string for packages using @code{git-fetch}.
+
+@example
+(git-version "0.0.0" "0" "93818c936ee7e2f1ba1b315578bde363a7d43d05")
+@result{} "0.0.0-0.93818c9"
+@end example
+@end deffn
+
 @deffn {Scheme Syntax} this-package
 When used in the @emph{lexical scope} of a package field definition, this
 identifier resolves to the package being defined.

base-commit: 3f2a4b098039bd374c76d524223de3c6c475f23e
-- 
2.31.1