guix-build: Allow version-qualified package names.

* guix-build.in (guix-build)[find-package]: New procedure.
  Use it instead of using `find-packages-by-name' directly.
  Suggested by Andreas Enge <andreas@enge.fr>.
* tests/guix-build.sh: Add tests.
* doc/guix.texi (Invoking guix-build): Add `coreutils-8.20' as an
  example.  Fix guile-1.8 example.

doc/guix.texi

@@ -989,8 +989,9 @@ guix-build @var{options} @var{package-or-derivation}@dots{}
 @end example
 
 @var{package-or-derivation} may be either the name of a package found in
-the software distribution such as @code{coreutils}, or a derivation such
-as @file{/nix/store/xxx-coreutils-8.19.drv}.  Alternatively, the
+the software distribution such as @code{coreutils} or
+@code{coreutils-8.20}, or a derivation such as
+@file{/nix/store/@dots{}-coreutils-8.19.drv}.  Alternatively, the
 @code{--expression} option may be used to specify a Scheme expression
 that evaluates to a package; this is useful when disambiguation among
 several same-named packages or package variants is needed.
@@ -1003,7 +1004,7 @@ The @var{options} may be zero or more of the following:
 @itemx -e @var{expr}
 Build the package @var{expr} evaluates to.
 
-For example, @var{expr} may be @code{(@@ (distro packages guile)
+For example, @var{expr} may be @code{(@@ (gnu packages guile)
 guile-1.8)}, which unambiguously designates this specific variant of
 version 1.8 of Guile.
 

guix-build.in

@@ -38,6 +38,7 @@ exec ${GUILE-@GUILE@} -L "@guilemoduledir@" -l "$0"    \
   #:use-module (ice-9 format)
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-11)
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-37)
@@ -195,6 +196,30 @@ Build the given PACKAGE-OR-DERIVATION and return their output paths.\n"))
                  root (strerror (system-error-errno args)))
          (exit 1)))))
 
+  (define (find-package request)
+    ;; Return a package matching REQUEST.  REQUEST may be a package
+    ;; name, or a package name followed by a hyphen and a version
+    ;; number.
+    (let-values (((name version)
+                  (package-name->name+version request)))
+      (match (find-packages-by-name name version)
+        ((p)                                      ; one match
+         p)
+        ((p _ ...)                                ; several matches
+         (format (current-error-port)
+                 (_ "warning: ambiguous package specification `~a'~%")
+                 request)
+         (format (current-error-port)
+                 (_ "warning: choosing ~a from ~a~%")
+                 (package-full-name p)
+                 (location->string (package-location p)))
+         p)
+        (_                                        ; no matches
+         (if version
+             (leave (_ "~A: package not found for version ~a~%")
+                    name version)
+             (leave (_ "~A: unknown package~%") name))))))
+
   (setlocale LC_ALL "")
   (textdomain "guix")
   (setvbuf (current-output-port) _IOLBF)
@@ -212,14 +237,12 @@ Build the given PACKAGE-OR-DERIVATION and return their output paths.\n"))
                                   (('argument . (? derivation-path? drv))
                                    drv)
                                   (('argument . (? string? x))
-                                   (match (find-packages-by-name x)
-                                     ((p _ ...)
-                                      (if src?
-                                          (let ((s (package-source p)))
-                                            (package-source-derivation (%store) s))
-                                          (package-derivation (%store) p sys)))
-                                     (_
-                                      (leave (_ "~A: unknown package~%") x))))
+                                   (let ((p (find-package x)))
+                                     (if src?
+                                         (let ((s (package-source p)))
+                                           (package-source-derivation
+                                            (%store) s))
+                                         (package-derivation (%store) p sys))))
                                   (_ #f))
                                  opts))
                (req  (append-map (lambda (drv-path)

tests/guix-build.sh

@@ -1,5 +1,5 @@
 # GNU Guix --- Functional package management for GNU
-# Copyright © 2012 Ludovic Courtès <ludo@gnu.org>
+# Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
 #
 # This file is part of GNU Guix.
 #
@@ -50,3 +50,11 @@ if guix-build -r "$result" -e '(@@ (gnu packages base) %bootstrap-guile)'
 then false; else true; fi
 
 rm -f "$result"
+
+# Parsing package names and versions.
+guix-build -n time		# PASS
+guix-build -n time-1.7		# PASS, version found
+if guix-build -n time-3.2;	# FAIL, version not found
+then false; else true; fi
+if guix-build -n something-that-will-never-exist; # FAIL
+then false; else true; fi