[bug#35905] [PATCH] find-package-by-name: reverse package load precedence

[bug#35905] [PATCH] find-package-by-name: reverse package load precedence

[Robert Vollmert]

From e484a11fa652c6e9cb4484c6f700b91f134e7156 Mon Sep 17 00:00:00 2001
From: Robert Vollmert <rob@vllmrt.net>
Date: Sat, 25 May 2019 08:40:38 +0200
Subject: [PATCH] guix: find-package-by-name: list modules in path order

A particular effect of this is that if there are ambiguous
packages in a directory specified with `-L module_dir` and the
distribution, the version from `module_dir` will be loaded,
which is usually what would be expected. (E.g. for `guix build`
or `guix package -i`.)

* guix/discovery.scm (all-modules): Return modules in path order.
* tests/guix-package.sh: Test local definitions take precedence.
---
 guix/discovery.scm    |  4 ++--
 tests/guix-package.sh | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/guix/discovery.scm b/guix/discovery.scm
index ef5ae73973..5bb494941b 100644
--- a/guix/discovery.scm
+++ b/guix/discovery.scm
@@ -145,8 +145,8 @@ Call (PROC MODULE RESULT) for each module that is found."
   "Return the list of package modules found in PATH, a list of directories to
 search.  Entries in PATH can be directory names (strings) or (DIRECTORY
 . SUB-DIRECTORY) pairs, in which case modules are searched for beneath
-SUB-DIRECTORY."
-  (fold-modules cons '() path #:warn warn))
+SUB-DIRECTORY. Modules are listed in the order they appear on the path."
+  (reverse (fold-modules cons '() path #:warn warn)))
 
 (define (fold-module-public-variables* proc init modules)
   "Call (PROC MODULE SYMBOL VARIABLE) for each variable exported by one of MODULES,
diff --git a/tests/guix-package.sh b/tests/guix-package.sh
index 767c3f8a66..79d6ec65e4 100644
--- a/tests/guix-package.sh
+++ b/tests/guix-package.sh
@@ -280,6 +280,20 @@ export GUIX_PACKAGE_PATH
 guix package -A emacs-foo-bar | grep 42
 guix package -i emacs-foo-bar@42 -n
 
+# Make sure GUIX_PACKAGE_PATH/'-L' takes precedence in case of duplicate packages.
+cat > "$module_dir/bar.scm"<<EOF
+(define-module (bar)
+  #:use-module (guix packages))
+
+(define-public hello
+  (package (inherit (@@ (gnu packages base) hello))
+    (synopsis "an overridden version of GNU hello")))
+EOF
+
+guix package -i hello -n 2>&1 | grep choosing.*bar.scm
+( unset GUIX_PACKAGE_PATH; \
+  guix package -i hello -n -L "$module_dir" 2>&1 | grep choosing.*bar.scm )
+
 # Make sure patches that live under $GUIX_PACKAGE_PATH are found.
 cat > "$module_dir/emacs.patch"<<EOF
 This is a fake patch.
-- 
2.21.0

bug#35905: [PATCH] find-package-by-name: reverse package load precedence

[Ludovic Courtès]

Hi Robert,

Robert Vollmert <rob@vllmrt.net> skribis:

> From e484a11fa652c6e9cb4484c6f700b91f134e7156 Mon Sep 17 00:00:00 2001
> From: Robert Vollmert <rob@vllmrt.net>
> Date: Sat, 25 May 2019 08:40:38 +0200
> Subject: [PATCH] guix: find-package-by-name: list modules in path order
>
> A particular effect of this is that if there are ambiguous
> packages in a directory specified with `-L module_dir` and the
> distribution, the version from `module_dir` will be loaded,
> which is usually what would be expected. (E.g. for `guix build`
> or `guix package -i`.)
>
> * guix/discovery.scm (all-modules): Return modules in path order.
> * tests/guix-package.sh: Test local definitions take precedence.

Good catch, applied!  (I adjusted the summary line so that it mentions
“discovery”.)

Likewise, in case more than one packages match a given spec, packages of
third-party channels would take precedence over those coming from the
‘guix’ channel, contrary to what was intended.

Thanks for fixing it!

Ludo’.