guix build: '-f' accepts file-like objects.

* guix/scripts/build.scm (options->things-to-build)[validate-type]:
Check for 'file-like?'.
(options->derivations): Accept 'file-like?'.
* tests/guix-build.sh: Add a test with 'computed-file'.
* doc/guix.texi (Additional Build Options): Mention file-like objects.

doc/guix.texi

@@ -6365,9 +6365,8 @@ retrieved using the @option{--log-file} option.
 
 @item --file=@var{file}
 @itemx -f @var{file}
-
-Build the package or derivation that the code within @var{file}
-evaluates to.
+Build the package, derivation, or other file-like object that the code within
+@var{file} evaluates to (@pxref{G-Expressions, file-like objects}).
 
 As an example, @var{file} might contain a package definition like this
 (@pxref{Defining Packages}):

guix/scripts/build.scm

@@ -623,7 +623,7 @@ must be one of 'package', 'all', or 'transitive'~%")
   "Read the arguments from OPTS and return a list of high-level objects to
 build---packages, gexps, derivations, and so on."
   (define (validate-type x)
-    (unless (or (package? x) (derivation? x) (gexp? x) (procedure? x))
+    (unless (or (derivation? x) (file-like? x) (gexp? x) (procedure? x))
       (leave (G_ "~s: not something we can build~%") x)))
 
   (define (ensure-list x)
@@ -700,6 +700,10 @@ package '~a' has no source~%")
                               (set-guile-for-build (default-guile))
                               (proc))
                             #:system system)))
+                   ((? file-like? obj)
+                    (list (run-with-store store
+                            (lower-object obj system
+                                          #:target (assoc-ref opts 'target)))))
                    ((? gexp? gexp)
                     (list (run-with-store store
                             (mbegin %store-monad

tests/guix-build.sh

@@ -221,6 +221,10 @@ guix build -e "(begin
 guix build -e '#~(mkdir #$output)' -d
 guix build -e '#~(mkdir #$output)' -d | grep 'gexp\.drv'
 
+# Same with a file-like object.
+guix build -e '(computed-file "foo" #~(mkdir #$output))' -d
+guix build -e '(computed-file "foo" #~(mkdir #$output))' -d | grep 'foo\.drv'
+
 # Building from a package file.
 cat > "$module_dir/package.scm"<<EOF
 (use-modules (gnu))