doc: Add a note reminder to checkout the correct tag for rust crates.

* doc/guix-cookbook.texi (Packaging Workflows)[Packaging Rust Crates]
{Common Workflow for Rust Packaging}: Add the note.

Change-Id: I670c78d7cd6771b5f4814123e488cbdb1c4e9fe2
Signed-off-by: Gabriel Wicki <gabriel@erlikon.ch>

1 files changed, 9 insertions, 0 deletions

diff --git a/doc/guix-cookbook.texi b/doc/guix-cookbook.texi
index 09a49a1c9a8..73b1e16b241 100644
--- a/doc/guix-cookbook.texi
+++ b/doc/guix-cookbook.texi
@@ -1709,6 +1709,15 @@ $ cargo audit
 $ cargo license
 @end example
 
+@quotation Note
+Before running @command{cargo generate-lockfile}, make sure you have checked
+out the correct tag for the version you are packaging. This ensures that
+@code{Cargo.toml} matches the file used in the packages's @code{source} field.
+To make sure, you can obtain the exact source with @command{./pre-inst-env guix
+build --source <package>} and only then run @command{cargo generate-lockfile} on
+that source tree.
+@end quotation
+
 @command{cargo generate-lockfile} updates dependencies to compatible versions.
 Applying it to all Rust applications helps reduce a great number of Rust
 libraries we need to check later.  Although sometimes libraries may fail to