derivations: Add #:local-build? parameter for derivations.

* guix/derivations.scm (derivation): Add #:local-build? parameter and
  honor it.
  (build-expression->derivation): Likewise.
* doc/guix.texi (Derivations): Update documentation of these
  procedures.

1 files changed, 13 insertions, 3 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 325467c82d..91fa07f1a8 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -1452,7 +1452,11 @@ derivations as Scheme objects, along with procedures to create and
 otherwise manipulate derivations.  The lowest-level primitive to create
 a derivation is the @code{derivation} procedure:
 
-@deffn {Scheme Procedure} derivation @var{store} @var{name} @var{builder} @var{args} [#:outputs '("out")] [#:hash #f] [#:hash-algo #f] [#:hash-mode #f] [#:inputs '()] [#:env-vars '()] [#:system (%current-system)] [#:references-graphs #f]
+@deffn {Scheme Procedure} derivation @var{store} @var{name} @var{builder} @
+  @var{args} [#:outputs '("out")] [#:hash #f] [#:hash-algo #f] @
+  [#:hash-mode #f] [#:inputs '()] [#:env-vars '()] @
+  [#:system (%current-system)] [#:references-graphs #f] @
+  [#:local-build? #f]
 Build a derivation with the given arguments, and return the resulting
 @code{<derivation>} object.
 
@@ -1464,6 +1468,11 @@ When @var{references-graphs} is true, it must be a list of file
 name/store path pairs.  In that case, the reference graph of each store
 path is exported in the build environment in the corresponding file, in
 a simple text format.
+
+When @var{local-build?} is true, declare that the derivation is not a
+good candidate for offloading and should rather be built locally
+(@pxref{Daemon Offload Setup}).  This is the case for small derivations
+where the costs of data transfers would outweigh the benefits.
 @end deffn
 
 @noindent
@@ -1494,7 +1503,7 @@ the caller to directly pass a Guile expression as the build script:
        [#:system (%current-system)] [#:inputs '()] @
        [#:outputs '("out")] [#:hash #f] [#:hash-algo #f] @
        [#:env-vars '()] [#:modules '()] @
-       [#:references-graphs #f] [#:guile-for-build #f]
+       [#:references-graphs #f] [#:local-build? #f] [#:guile-for-build #f]
 Return a derivation that executes Scheme expression @var{exp} as a
 builder for derivation @var{name}.  @var{inputs} must be a list of
 @code{(name drv-path sub-drv)} tuples; when @var{sub-drv} is omitted,
@@ -1516,7 +1525,8 @@ terminates by passing the result of @var{exp} to @code{exit}; thus, when
 @var{guile-for-build} is omitted or is @code{#f}, the value of the
 @code{%guile-for-build} fluid is used instead.
 
-See the @code{derivation} procedure for the meaning of @var{references-graphs}.
+See the @code{derivation} procedure for the meaning of @var{references-graphs}
+and @var{local-build?}.
 @end deffn
 
 @noindent