01/02: store: 'references/substitutes' correctly handles the order of substitutes.

[Ludovic Courtès]

civodul pushed a commit to branch master
in repository guix.

commit dd78e90a4dcd1e637b56ae278c4e631ccb384ee0
Author: Ludovic Courtès <address@hidden>
Date:   Sat Mar 5 22:01:33 2016 +0100

    store: 'references/substitutes' correctly handles the order of substitutes.
    
    Before that, 'references/substitutes' would assume that
    'substitutable-path-info' would return things in the same order as its
    arguments, which is not the case.  Thus, it would sometimes provide
    incorrect reference information, occasionally leading to infinite
    loop (because dependency information would denote cycles.)
    
    Fixes <http://bugs.gnu.org/22914>.
    Reported by Eric Bavier <address@hidden>.
    
    * guix/store.scm (references/substitutes): Make ITEMS the first argument
    of the loop; match on it.  Use 'any' to find a matching substitute.
    (substitutable-path-info): Clarify docstring about ordering.
---
 guix/store.scm |   28 ++++++++++++++++++----------
 1 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/guix/store.scm b/guix/store.scm
index 56aa38b..a220b6e 100644
--- a/guix/store.scm
+++ b/guix/store.scm
@@ -752,18 +752,24 @@ the list of references")
                          (status 1)))))
 
     ;; Intersperse SUBSTS and LOCAL-REFS.
-    (let loop ((local-refs  local-refs)
-               (remote-refs (map substitutable-references substs))
+    (let loop ((items       items)
+               (local-refs  local-refs)
                (result      '()))
-      (match local-refs
+      (match items
         (()
          (reverse result))
-        ((#f tail ...)
-         (match remote-refs
-           ((remote rest ...)
-            (loop tail rest (cons remote result)))))
-        ((head tail ...)
-         (loop tail remote-refs (cons head result)))))))
+        ((item items ...)
+         (match local-refs
+           ((#f tail ...)
+            (loop items tail
+                  (cons (any (lambda (subst)
+                               (and (string=? (substitutable-path subst) item)
+                                    (substitutable-references subst)))
+                             substs)
+                        result)))
+           ((head tail ...)
+            (loop items tail
+                  (cons head result)))))))))
 
 (define* (fold-path store proc seed path
                     #:optional (relatives (cut references store <>)))
@@ -852,7 +858,9 @@ topological order."
   (operation (query-substitutable-path-infos (store-path-list paths))
              "Return information about the subset of PATHS that is
 substitutable.  For each substitutable path, a `substitutable?' object is
-returned."
+returned; thus, the resulting list can be shorter than PATHS.  Furthermore,
+that there is no guarantee that the order of the resulting list matches the
+order of PATHS."
              substitutable-path-list))
 
 (define-operation (optimize-store)