derivations: Add properties.

* guix/derivations.scm (derivation): Add #:properties parameter.
[user+system-env-vars]: Honor it.
(derivation-properties): New procedure.
(build-expression->derivation): Add #:properties and pass it to
'derivation'.
* guix/gexp.scm (gexp->derivation): Likewise.
* tests/derivations.scm ("derivation-properties"): New test.
* tests/gexp.scm ("gexp->derivation properties"): New test.
* doc/guix.texi (Derivations, G-Expressions): Adjust accordingly.

doc/guix.texi

@@ -5060,7 +5060,7 @@ a derivation is the @code{derivation} procedure:
   [#:system (%current-system)] [#:references-graphs #f] @
   [#:allowed-references #f] [#:disallowed-references #f] @
   [#:leaked-env-vars #f] [#:local-build? #f] @
-  [#:substitutable? #t]
+  [#:substitutable? #t] [#:properties '()]
 Build a derivation with the given arguments, and return the resulting
 @code{<derivation>} object.
 
@@ -5097,6 +5097,9 @@ When @var{substitutable?} is false, declare that substitutes of the
 derivation's output should not be used (@pxref{Substitutes}).  This is
 useful, for instance, when building packages that capture details of the
 host CPU instruction set.
+
+@var{properties} must be an association list describing ``properties'' of the
+derivation.  It is kept as-is, uninterpreted, in the derivation.
 @end deffn
 
 @noindent
@@ -5790,7 +5793,8 @@ information about monads.)
        [#:leaked-env-vars #f] @
        [#:script-name (string-append @var{name} "-builder")] @
        [#:deprecation-warnings #f] @
-       [#:local-build? #f] [#:substitutable? #t] [#:guile-for-build #f]
+       [#:local-build? #f] [#:substitutable? #t] @
+       [#:properties '()] [#:guile-for-build #f]
 Return a derivation @var{name} that runs @var{exp} (a gexp) with
 @var{guile-for-build} (a derivation) on @var{system}; @var{exp} is
 stored in a file called @var{script-name}.  When @var{target} is true,

guix/derivations.scm

@@ -80,6 +80,7 @@
             substitutable-derivation?
             substitution-oracle
             derivation-hash
+            derivation-properties
 
             read-derivation
             read-derivation-from-file
@@ -681,7 +682,8 @@ name of each input with that input's hash."
                      references-graphs
                      allowed-references disallowed-references
                      leaked-env-vars local-build?
-                     (substitutable? #t))
+                     (substitutable? #t)
+                     (properties '()))
   "Build a derivation with the given arguments, and return the resulting
 <derivation> object.  When HASH and HASH-ALGO are given, a
 fixed-output derivation is created---i.e., one whose result is known in
@@ -708,7 +710,10 @@ for offloading and should rather be built locally.  This is the case for small
 derivations where the costs of data transfers would outweigh the benefits.
 
 When SUBSTITUTABLE? is false, declare that substitutes of the derivation's
-output should not be used."
+output should not be used.
+
+PROPERTIES must be an association list describing \"properties\" of the
+derivation.  It is kept as-is, uninterpreted, in the derivation."
   (define (add-output-paths drv)
     ;; Return DRV with an actual store path for each of its output and the
     ;; corresponding environment variable.
@@ -763,6 +768,10 @@ output should not be used."
                             `(("impureEnvVars"
                                . ,(string-join leaked-env-vars)))
                             '())
+                      ,@(match properties
+                          (() '())
+                          (lst `(("guix properties"
+                                  . ,(object->string properties)))))
                       ,@env-vars)))
       (match references-graphs
         (((file . path) ...)
@@ -851,6 +860,14 @@ long-running processes that know what they're doing.  Use with care!"
   (invalidate-memoization! derivation-path->base16-hash)
   (hash-clear! %derivation-cache))
 
+(define derivation-properties
+  (mlambdaq (drv)
+    "Return the property alist associated with DRV."
+    (match (assoc "guix properties"
+                  (derivation-builder-environment-vars drv))
+      ((_ . str) (call-with-input-string str read))
+      (#f        '()))))
+
 (define* (map-derivation store drv mapping
                          #:key (system (%current-system)))
   "Given MAPPING, a list of pairs of derivations, return a derivation based on
@@ -1129,7 +1146,8 @@ they can refer to each other."
                                        references-graphs
                                        allowed-references
                                        disallowed-references
-                                       local-build? (substitutable? #t))
+                                       local-build? (substitutable? #t)
+                                       (properties '()))
   "Return a derivation that executes Scheme expression EXP as a builder
 for derivation NAME.  INPUTS must be a list of (NAME DRV-PATH SUB-DRV)
 tuples; when SUB-DRV is omitted, \"out\" is assumed.  MODULES is a list
@@ -1149,7 +1167,8 @@ EXP is built using GUILE-FOR-BUILD (a derivation).  When GUILE-FOR-BUILD is
 omitted or is #f, the value of the `%guile-for-build' fluid is used instead.
 
 See the `derivation' procedure for the meaning of REFERENCES-GRAPHS,
-ALLOWED-REFERENCES, DISALLOWED-REFERENCES, LOCAL-BUILD?, and SUBSTITUTABLE?."
+ALLOWED-REFERENCES, DISALLOWED-REFERENCES, LOCAL-BUILD?, SUBSTITUTABLE?,
+and PROPERTIES."
   (define guile-drv
     (or guile-for-build (%guile-for-build)))
 
@@ -1277,7 +1296,8 @@ ALLOWED-REFERENCES, DISALLOWED-REFERENCES, LOCAL-BUILD?, and SUBSTITUTABLE?."
                 #:allowed-references allowed-references
                 #:disallowed-references disallowed-references
                 #:local-build? local-build?
-                #:substitutable? substitutable?)))
+                #:substitutable? substitutable?
+                #:properties properties)))
 
 
 ;;;

guix/gexp.scm

@@ -631,6 +631,7 @@ names and file names suitable for the #:allowed-references argument to
                            allowed-references disallowed-references
                            leaked-env-vars
                            local-build? (substitutable? #t)
+                           (properties '())
 
                            ;; TODO: This parameter is transitional; it's here
                            ;; to avoid a full rebuild.  Remove it on the next
@@ -800,7 +801,8 @@ The other arguments are as for 'derivation'."
                       #:disallowed-references disallowed
                       #:leaked-env-vars leaked-env-vars
                       #:local-build? local-build?
-                      #:substitutable? substitutable?))))
+                      #:substitutable? substitutable?
+                      #:properties properties))))
 
 (define* (gexp-inputs exp #:key native?)
   "Return the input list for EXP.  When NATIVE? is true, return only native

tests/derivations.scm

@@ -1132,6 +1132,16 @@
                                     ((p2 . _)
                                      (string<? p1 p2)))))))))))))
 
+(test-equal "derivation-properties"
+  (list '() '((type . test)))
+  (let ((drv1 (build-expression->derivation %store "bar"
+                                            '(mkdir %output)))
+        (drv2 (build-expression->derivation %store "foo"
+                                           '(mkdir %output)
+                                           #:properties '((type . test)))))
+    (list (derivation-properties drv1)
+          (derivation-properties drv2))))
+
 (test-equal "map-derivation"
   "hello"
   (let* ((joke (package-derivation %store guile-1.8))

tests/gexp.scm

@@ -476,7 +476,15 @@
     (return (and (string=? (readlink (string-append out "/foo")) guile)
                  (string=? (readlink out2) file)
                  (equal? refs (list (dirname (dirname guile))))
-                 (equal? refs2 (list file))))))
+                 (equal? refs2 (list file))
+                 (null? (derivation-properties drv))))))
+
+(test-assertm "gexp->derivation properties"
+  (mlet %store-monad ((drv (gexp->derivation "foo"
+                                             #~(mkdir #$output)
+                                             #:properties '((type . test)))))
+    (return (equal? '((type . test))
+                    (derivation-properties drv)))))
 
 (test-assertm "gexp->derivation vs. grafts"
   (mlet* %store-monad ((graft?  (set-grafting #f))