guix package: Add optional argument to --search-paths.

* guix/scripts/package.scm (search-path-environment-variables): Add #:kind
  parameter.  Pass it to 'environment-variable-definition'.
  (display-search-paths): Add #:kind parameter and pass it to
  'search-path-environment-variables'.
  (%options): Add an optional parameter for "--search-paths".
  (guix-package)[process-query]: Handle it.
* tests/guix-package-net.sh: Adjust existing test.
* tests/guix-package.sh: Adjust existing tests and add new test.
* doc/guix.texi (Invoking guix package): Document it.

doc/guix.texi

@@ -1098,7 +1098,7 @@ The difference between @code{--roll-back} and
 not make a zeroth generation, so if a specified generation does not
 exist, the current generation will not be changed.
 
-@item --search-paths
+@item --search-paths[=@var{kind}]
 @cindex search paths
 Report environment variable definitions, in Bash syntax, that may be
 needed in order to use the set of installed packages.  These environment
@@ -1113,6 +1113,18 @@ library are installed in the profile, then @code{--search-paths} will
 suggest setting these variables to @code{@var{profile}/include} and
 @code{@var{profile}/lib}, respectively.
 
+The typical use case is to define these environment variables in the
+shell:
+
+@example
+$ eval `guix package --search-paths`
+@end example
+
+@var{kind} may be one of @code{exact}, @code{prefix}, or @code{suffix},
+meaning that the returned environment variable definitions will either
+be exact settings, or prefixes or suffixes of the current value of these
+variables.  When omitted, @var{kind} defaults to @code{exact}.
+
 @item --profile=@var{profile}
 @itemx -p @var{profile}
 Use @var{profile} instead of the user's default profile.

guix/scripts/package.scm

@@ -376,10 +376,13 @@ (define (upgradeable? name current-version current-path)
 ;;;
 
 (define* (search-path-environment-variables entries profile
-                                            #:optional (getenv getenv))
+                                            #:optional (getenv getenv)
+                                            #:key (kind 'exact))
   "Return environment variable definitions that may be needed for the use of
 ENTRIES, a list of manifest entries, in PROFILE.  Use GETENV to determine the
-current settings and report only settings not already effective."
+current settings and report only settings not already effective.  KIND
+must be one of 'exact, 'prefix, or 'suffix, depending on the kind of search
+path definition to be returned."
   (let ((search-paths (delete-duplicates
                        (cons $PATH
                              (append-map manifest-entry-search-paths
@@ -388,17 +391,19 @@ (define* (search-path-environment-variables entries profile
                   ((spec . value)
                    (let ((variable (search-path-specification-variable spec))
                          (sep      (search-path-specification-separator spec)))
-                     ;; TODO: Offer the choice between exact/prefix/suffix.
                      (environment-variable-definition variable value
-                                                      #:separator sep))))
+                                                      #:separator sep
+                                                      #:kind kind))))
                 (evaluate-search-paths search-paths (list profile)
                                        getenv))))
 
-(define (display-search-paths entries profile)
+(define* (display-search-paths entries profile
+                               #:key (kind 'exact))
   "Display the search path environment variables that may need to be set for
 ENTRIES, a list of manifest entries, in the context of PROFILE."
   (let* ((profile  (user-friendly-profile profile))
-         (settings (search-path-environment-variables entries profile)))
+         (settings (search-path-environment-variables entries profile
+                                                      #:kind kind)))
     (unless (null? settings)
       (format #t (_ "The following environment variable definitions may be needed:~%"))
       (format #t "~{   ~a~%~}" settings))))
@@ -533,10 +538,20 @@ (define %options
                  (lambda (opt name arg result arg-handler)
                    (values (alist-cons 'switch-generation arg result)
                            #f)))
-         (option '("search-paths") #f #f
+         (option '("search-paths") #f #t
                  (lambda (opt name arg result arg-handler)
-                   (values (cons `(query search-paths) result)
-                           #f)))
+                   (let ((kind (match arg
+                                 ((or "exact" "prefix" "suffix")
+                                  (string->symbol arg))
+                                 (#f
+                                  'exact)
+                                 (x
+                                  (leave (_ "~a: unsupported \
+kind of search path~%")
+                                         x)))))
+                     (values (cons `(query search-paths ,kind)
+                                   result)
+                             #f))))
          (option '(#\p "profile") #t #f
                  (lambda (opt name arg result arg-handler)
                    (values (alist-cons 'profile (canonicalize-profile arg)
@@ -977,12 +992,13 @@ (define (list-generation number)
                       (find-packages-by-name name version)))
            #t))
 
-        (('search-paths)
+        (('search-paths kind)
          (let* ((manifest (profile-manifest profile))
                 (entries  (manifest-entries manifest))
                 (profile  (user-friendly-profile profile))
                 (settings (search-path-environment-variables entries profile
-                                                             (const #f))))
+                                                             (const #f)
+                                                             #:kind kind)))
            (format #t "~{~a~%~}" settings)
            #t))
 

tests/guix-package-net.sh

@@ -147,7 +147,7 @@ test "`readlink_base "$profile"`" = "$profile-2-link"
 
 # Make sure LIBRARY_PATH gets listed by `--search-paths'.
 guix package --bootstrap -p "$profile" -i guile-bootstrap -i gcc-bootstrap
-guix package --search-paths -p "$profile" | grep LIBRARY_PATH
+guix package -p "$profile" --search-paths | grep LIBRARY_PATH
 
 # Roll back so we can delete #3 below.
 guix package -p "$profile" --switch-generation=2

tests/guix-package.sh

@@ -52,8 +52,13 @@ test -L "$profile" && test -L "$profile-1-link"
 test -f "$profile/bin/guile"
 
 # No search path env. var. here.
-guix package --search-paths -p "$profile"
-test "`guix package --search-paths -p "$profile" | wc -l`" = 0
+guix package -p "$profile" --search-paths
+guix package -p "$profile" --search-paths | grep '^export PATH='
+test "`guix package -p "$profile" --search-paths | wc -l`" = 1  # $PATH
+( set -e; set -x;						\
+  eval `guix package --search-paths=prefix -p "$PWD/$profile"`;	\
+  test "`type -P guile`" = "$PWD/$profile/bin/guile" ;		\
+  type -P rm )
 
 # Exit with 1 when a generation does not exist.
 if guix package -p "$profile" --delete-generations=42;