packages: Better preserve object identity when rewriting.

Fixes a bug whereby the presence of propagated inputs could lead to two
non-eq? but actually equal packages in a bag's inputs.  The problem
would manifest itself when running, for instance:

  guix build inkscape -d --with-graft=glib=glib-networking --no-grafts

The resulting derivation would differ due from that without
'--with-graft'.  This was due to the fact that glib propagates libffi;
this instance of libffi was not rewritten even though other instances in
the graph were rewritten.  Thus, glib would end up with two non-eq?
libffi instances, which in turn would lead to duplicate entries in its
'%build-inputs' variable.

Fixes <https://bugs.gnu.org/43890>.

* guix/packages.scm (package-mapping)[rewrite]: Remove call to 'cut?'
and call 'replace' unconditionally.
[replace]: Add 'cut?' case.
* tests/guix-build.sh: Add test combining '--no-grafts' and
'--with-graft'.
* tests/packages.scm ("package-input-rewriting/spec, identity")
("package-input-rewriting, identity"): New tests.

2 files changed, 49 insertions, 0 deletions

diff --git a/tests/guix-build.sh b/tests/guix-build.sh
index 4a58ea1476..b7602e668c 100644
--- a/tests/guix-build.sh
+++ b/tests/guix-build.sh
@@ -289,6 +289,12 @@ drv1=`guix build glib -d`
 drv2=`guix build glib -d --with-input=libreoffice=inkscape`
 test "$drv1" = "$drv2"
 
+# '--with-graft' should have no effect when using '--no-grafts'.
+# See <https://bugs.gnu.org/43890>.
+drv1=`guix build inkscape -d --no-grafts`
+drv2=`guix build inkscape -d --no-grafts --with-graft=glib=glib-networking`
+test "$drv1" = "$drv2"
+
 # Rewriting implicit inputs.
 drv1=`guix build hello -d`
 drv2=`guix build hello -d --with-input=gcc=gcc-toolchain`
diff --git a/tests/packages.scm b/tests/packages.scm
index 2d13d91344..18e8e16e74 100644
--- a/tests/packages.scm
+++ b/tests/packages.scm
@@ -1450,6 +1450,49 @@
             (eq? foo grep)
             (eq? bar dep))))))
 
+(test-assert "package-input-rewriting/spec, identity"
+  ;; Make sure that 'package-input-rewriting/spec' doesn't gratuitously
+  ;; introduce variants.  In this case, the LIBFFI propagated input should not
+  ;; be duplicated when passing GOBJECT through REWRITE.
+  ;; See <https://issues.guix.gnu.org/43890>.
+  (let* ((libffi  (dummy-package "libffi"
+                    (build-system trivial-build-system)))
+         (glib    (dummy-package "glib"
+                    (build-system trivial-build-system)
+                    (propagated-inputs `(("libffi" ,libffi)))))
+         (gobject (dummy-package "gobject-introspection"
+                    (build-system trivial-build-system)
+                    (inputs `(("glib" ,glib)))
+                    (propagated-inputs `(("libffi" ,libffi)))))
+         (rewrite (package-input-rewriting/spec
+                   `(("glib" . ,identity)))))
+    (and (= (length (package-transitive-inputs gobject))
+            (length (package-transitive-inputs (rewrite gobject))))
+         (string=? (derivation-file-name
+                    (package-derivation %store (rewrite gobject)))
+                   (derivation-file-name
+                    (package-derivation %store gobject))))))
+
+(test-assert "package-input-rewriting, identity"
+  ;; Similar to the test above, but with 'package-input-rewriting'.
+  ;; See <https://issues.guix.gnu.org/43890>.
+  (let* ((libffi  (dummy-package "libffi"
+                    (build-system trivial-build-system)))
+         (glib    (dummy-package "glib"
+                    (build-system trivial-build-system)
+                    (propagated-inputs `(("libffi" ,libffi)))))
+         (gobject (dummy-package "gobject-introspection"
+                    (build-system trivial-build-system)
+                    (inputs `(("glib" ,glib)))
+                    (propagated-inputs `(("libffi" ,libffi)))))
+         (rewrite (package-input-rewriting `((,glib . ,glib)))))
+    (and (= (length (package-transitive-inputs gobject))
+            (length (package-transitive-inputs (rewrite gobject))))
+         (string=? (derivation-file-name
+                    (package-derivation %store (rewrite gobject)))
+                   (derivation-file-name
+                    (package-derivation %store gobject))))))
+
 (test-equal "package-patched-vulnerabilities"
   '(("CVE-2015-1234")
     ("CVE-2016-1234" "CVE-2018-4567")