doc: Document that source derivation builds can be checked.

It is a common mistake to modify an <origin> record that computes to a
fixed-output derivation, forgetting to update its hash field, only to find out
that a previously built source gets used instead.  While there doesn't seem to
be an obvious solution to this problem, we can at least document the fact that
sources can be checked the same as other builds.

* doc/guix.texi (Additional Build Options): Document that source derivation
builds can be verified using --check.

1 files changed, 7 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index e7277fc9ee..889f380108 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -10424,6 +10424,13 @@ The returned source tarball is the result of applying any patches and
 code snippets specified in the package @code{origin} (@pxref{Defining
 Packages}).
 
+@cindex source, verification
+As with other derivations, the result of building a source derivation
+can be verified using the @option{--check} option (@pxref{build-check}).
+This is useful to validate that a (potentially already built or
+substituted, thus cached) package source matches against its declared
+hash.
+
 Note that @command{guix build -S} compiles the sources only of the
 specified packages.  They do not include the sources of statically
 linked dependencies and by themselves are insufficient for reproducing