05/11: store: Add 'references/cached'.

[guix-commits]

civodul pushed a commit to branch master
in repository guix.

commit c70cf1a724fb15e108dc842413db15a0b9f4bc10
Author: Ludovic Courtès <address@hidden>
AuthorDate: Sun Mar 29 01:21:32 2020 +0100

    store: Add 'references/cached'.
    
    * guix/store.scm (references/cached): New procedure.
---
 guix/store.scm | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/guix/store.scm b/guix/store.scm
index b3641ef..ca8c0e5 100644
--- a/guix/store.scm
+++ b/guix/store.scm
@@ -135,6 +135,7 @@
 
             built-in-builders
             references
+            references/cached
             references/substitutes
             references*
             query-path-info*
@@ -1393,6 +1394,13 @@ error if there is no such root."
   ;; would use a cache associated with the daemon connection instead (XXX).
   (make-hash-table 100))
 
+(define (references/cached store item)
+  "Like 'references', but cache results."
+  (or (hash-ref %reference-cache item)
+      (let ((references (references store item)))
+        (hash-set! %reference-cache item references)
+        references)))
+
 (define (references/substitutes store items)
   "Return the list of list of references of ITEMS; the result has the same
 length as ITEMS.  Query substitute information for any item missing from the