store: Add 'build-things'.

* guix/store.scm (operation-id): Rename 'build-derivations' to
  'build-things', as per Nix commit 1aba0bf0.
  (build-derivations): Rename to...
  (build-things): ... this.  Keep 'build-derivations' as an alias.
  (build): New procedure.
* tests/store.scm ("build-things with output path",
  "substitute + build-things with output path"): New tests.

guix/store.scm

@@ -62,6 +62,8 @@
             hash-part->path
             add-text-to-store
             add-to-store
+            build-things
+            build
             build-derivations
             add-temp-root
             add-indirect-root
@@ -140,7 +142,7 @@
   (query-referrers 6)
   (add-to-store 7)
   (add-text-to-store 8)
-  (build-derivations 9)
+  (build-things 9)
   (ensure-path 10)
   (add-temp-root 11)
   (add-indirect-root 12)
@@ -573,11 +575,16 @@ kept.  HASH-ALGO must be a string such as \"sha256\"."
               (hash-set! cache args path)
               path))))))
 
-(define-operation (build-derivations (string-list derivations))
+(define-operation (build-things (string-list things))
-  "Build DERIVATIONS, and return when the worker is done building them.
+  "Build THINGS, a list of store items which may be either '.drv' files or
+outputs, and return when the worker is done building them.  Elements of THINGS
+that are not derivations can only be substituted and not built locally.
 Return #t on success."
   boolean)
 
+;; Deprecated name for 'build-things'.
+(define build-derivations build-things)
+
 (define-operation (add-temp-root (store-path path))
   "Make PATH a temporary root for the duration of the current session.
 Return #t."
@@ -907,6 +914,10 @@ permission bits are kept."
                           recursive? "sha256" file)
             store)))
 
+(define build
+  ;; Monadic variant of 'build-things'.
+  (store-lift build-things))
+
 (define %guile-for-build
   ;; The derivation of the Guile to be used within the build environment,
   ;; when using 'gexp->derivation' and co.

tests/store.scm

@@ -306,6 +306,24 @@
            (null? (substitutable-paths s o))
            (null? (substitutable-path-info s o))))))
 
+(test-assert "build-things with output path"
+  (with-store s
+    (let* ((c   (random-text))                    ;contents of the output
+           (d   (build-expression->derivation
+                 s "substitute-me"
+                 `(call-with-output-file %output
+                    (lambda (p)
+                      (display ,c p)))
+                 #:guile-for-build
+                 (package-derivation s %bootstrap-guile (%current-system))))
+           (o   (derivation->output-path d)))
+      (set-build-options s #:use-substitutes? #f)
+
+      ;; Pass 'build-things' the output file name, O.  However, since there
+      ;; are no substitutes for O, it will just do nothing.
+      (build-things s (list o))
+      (not (valid-path? s o)))))
+
 (test-skip (if (getenv "GUIX_BINARY_SUBSTITUTE_URL") 0 1))
 
 (test-assert "substitute query"
@@ -350,6 +368,25 @@
              (build-derivations s (list d))
              (equal? c (call-with-input-file o get-string-all)))))))
 
+(test-assert "substitute + build-things with output path"
+  (with-store s
+    (let* ((c   (random-text))                    ;contents of the output
+           (d   (build-expression->derivation
+                 s "substitute-me"
+                 `(call-with-output-file %output
+                    (lambda (p)
+                      (exit 1)                    ;would actually fail
+                      (display ,c p)))
+                 #:guile-for-build
+                 (package-derivation s %bootstrap-guile (%current-system))))
+           (o   (derivation->output-path d)))
+      (with-derivation-substitute d c
+        (set-build-options s #:use-substitutes? #t)
+        (and (has-substitutes? s o)
+             (build-things s (list o))            ;give the output path
+             (valid-path? s o)
+             (equal? c (call-with-input-file o get-string-all)))))))
+
 (test-assert "substitute, corrupt output hash"
   ;; Tweak the substituter into installing a substitute whose hash doesn't
   ;; match the one announced in the narinfo.  The daemon must notice this and