grafts: Move '%graft?' and related bindings to (guix store).

The goal is to allow (guix grafts) to use (guix gexp) without
introducing a cycle between these two modules.

* guix/grafts.scm (%graft?, call-without-grafting, without-grafting)
(set-grafting, grafting?): Move to...
* guix/store.scm: ... here.

1 files changed, 36 insertions, 0 deletions

diff --git a/guix/store.scm b/guix/store.scm
index 4d21c5ff1a..a36dce416e 100644
--- a/guix/store.scm
+++ b/guix/store.scm
@@ -182,6 +182,11 @@
             interned-file
             interned-file-tree
 
+            %graft?
+            without-grafting
+            set-grafting
+            grafting?
+
             %store-prefix
             store-path
             output-path
@@ -2173,6 +2178,37 @@ connection, and return the result."
 
 
 ;;;
+;;; Whether to enable grafts.
+;;;
+
+(define %graft?
+  ;; Whether to honor package grafts by default.
+  (make-parameter #t))
+
+(define (call-without-grafting thunk)
+  (lambda (store)
+    (values (parameterize ((%graft? #f))
+              (run-with-store store (thunk)))
+            store)))
+
+(define-syntax-rule (without-grafting mexp ...)
+  "Bind monadic expressions MEXP in a dynamic extent where '%graft?' is
+false."
+  (call-without-grafting (lambda () (mbegin %store-monad mexp ...))))
+
+(define-inlinable (set-grafting enable?)
+  ;; This monadic procedure enables grafting when ENABLE? is true, and
+  ;; disables it otherwise.  It returns the previous setting.
+  (lambda (store)
+    (values (%graft? enable?) store)))
+
+(define-inlinable (grafting?)
+  ;; Return a Boolean indicating whether grafting is enabled.
+  (lambda (store)
+    (values (%graft?) store)))
+
+
+;;;
 ;;; Store paths.
 ;;;