From 36754eee28187b41e9a6ef15cd3c9911449a4e8d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Fri, 15 Feb 2019 22:58:29 +0100
Subject: [PATCH] packages: Remove duplicates from package cache.

Previously the same package could appear several times if several
variables were bound to it, as is notably the case for "python"
currently.  This, in turn, would lead to obnoxious "ambiguous package
specification" messages.

* gnu/packages.scm (generate-package-cache)[expand-cache]: Change RESULT
to RESULT+SEEN and adjust accordingly.
Call 'first' on the result of 'fold-module-public-variables*'.
* tests/packages.scm ("fold-available-packages with/without cache"):
Check for lack of duplicates in FROM-CACHE.
---
 gnu/packages.scm   | 53 ++++++++++++++++++++++++++--------------------
 tests/packages.scm |  3 ++-
 2 files changed, 32 insertions(+), 24 deletions(-)

diff --git a/gnu/packages.scm b/gnu/packages.scm
index a1814205f9..7b17e70c53 100644
--- a/gnu/packages.scm
+++ b/gnu/packages.scm
@@ -371,34 +371,41 @@ (define (generate-package-cache directory)
   (define cache-file
     (string-append directory %package-cache-file))
 
-  (define (expand-cache module symbol variable result)
+  (define (expand-cache module symbol variable result+seen)
     (match (false-if-exception (variable-ref variable))
       ((? package? package)
-       (if (hidden-package? package)
-           result
-           (cons `#(,(package-name package)
-                    ,(package-version package)
-                    ,(module-name module)
-                    ,symbol
-                    ,(package-outputs package)
-                    ,(->bool (member (%current-system)
-                                     (package-supported-systems package)))
-                    ,(->bool (package-superseded package))
-                    ,@(let ((loc (package-location package)))
-                        (if loc
-                            `(,(location-file loc)
-                              ,(location-line loc)
-                              ,(location-column loc))
-                            '(#f #f #f))))
-                 result)))
+       (match result+seen
+         ((result . seen)
+          (if (or (vhash-assq package seen)
+                  (hidden-package? package))
+              (cons result seen)
+              (cons (cons `#(,(package-name package)
+                             ,(package-version package)
+                             ,(module-name module)
+                             ,symbol
+                             ,(package-outputs package)
+                             ,(->bool
+                               (member (%current-system)
+                                       (package-supported-systems package)))
+                             ,(->bool (package-superseded package))
+                             ,@(let ((loc (package-location package)))
+                                 (if loc
+                                     `(,(location-file loc)
+                                       ,(location-line loc)
+                                       ,(location-column loc))
+                                     '(#f #f #f))))
+                          result)
+                    (vhash-consq package #t seen))))))
       (_
-       result)))
+       result+seen)))
 
   (define exp
-    (fold-module-public-variables* expand-cache '()
-                                   (all-modules (%package-module-path)
-                                                #:warn
-                                                warn-about-load-error)))
+    (first
+     (fold-module-public-variables* expand-cache
+                                    (cons '() vlist-null)
+                                    (all-modules (%package-module-path)
+                                                 #:warn
+                                                 warn-about-load-error))))
 
   (mkdir-p (dirname cache-file))
   (call-with-output-file cache-file
diff --git a/tests/packages.scm b/tests/packages.scm
index e5704ae4b9..4e4bffc48c 100644
--- a/tests/packages.scm
+++ b/tests/packages.scm
@@ -1037,7 +1037,8 @@ (define from-cache
                                                       result))
                                               '()))))))
 
-    (lset= equal? no-cache from-cache)))
+    (and (equal? (delete-duplicates from-cache) from-cache)
+         (lset= equal? no-cache from-cache))))
 
 (test-assert "find-packages-by-name"
   (match (find-packages-by-name "hello")