scripts: build: Add --file option.

* guix/scripts/build.scm (show-help): Add help text for --file option.
  (%options): Add --file option.
  (options/resolve-packages): Handle 'file' options.
* tests/guix-build.sh: Add tests.
* doc/guix.texi ("invoking guix build"): Add doc.

1 files changed, 13 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 1bb7125fa27..9878b93ddba 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -3615,6 +3615,19 @@ The @var{options} may be zero or more of the following:
 
 @table @code
 
+@item --file=@var{file}
+@itemx -f @var{file}
+
+Build the package or derivation that the code within @var{file}
+evaluates to.
+
+As an example, @var{file} might contain a package definition like this
+(@pxref{Defining Packages}):
+
+@example
+@verbatiminclude package-hello.scm
+@end example
+
 @item --expression=@var{expr}
 @itemx -e @var{expr}
 Build the package or derivation @var{expr} evaluates to.