ui: Make package outputs searchable.

* guix/ui.scm (relevance): Allow the "field" procedure of a metric to
return a list, and handle that case appropriately.  Update docstring.
(%package-metrics): Add a metric for package outputs.
* guix/scripts/package.scm (find-packages-by-description): Update
docstring.
* tests/guix-package.sh: Add a test case to verify that package outputs are
included in search results.

Co-authored-by: Tobias Geerinckx-Rice <me@tobias.gr>

guix/scripts/package.scm

@@ -180,9 +180,9 @@ hooks\" run when building the profile."
 ;;;
 
 (define (find-packages-by-description regexps)
-  "Return two values: the list of packages whose name, synopsis, or
-description matches at least one of REGEXPS sorted by relevance, and the list
-of relevance scores."
+  "Return two values: the list of packages whose name, synopsis, description,
+or output matches at least one of REGEXPS sorted by relevance, and the list of
+relevance scores."
   (let ((matches (fold-packages (lambda (package result)
                                   (if (package-superseded package)
                                       result

guix/ui.scm

@@ -11,6 +11,8 @@
 ;;; Copyright © 2016 Benz Schenk <benz.schenk@uzh.ch>
 ;;; Copyright © 2018 Kyle Meyer <kyle@kyleam.com>
 ;;; Copyright © 2018 Ricardo Wurmus <rekado@elephly.net>
+;;; Copyright © 2019 Chris Marusich <cmmarusich@gmail.com>
+;;; Copyright © 2019 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -1370,9 +1372,9 @@ WIDTH columns.  EXTRA-FIELDS is a list of symbol/value pairs to emit."
 (define (relevance obj regexps metrics)
   "Compute a \"relevance score\" for OBJ as a function of its number of
 matches of REGEXPS and accordingly to METRICS.  METRICS is list of
-field/weight pairs, where FIELD is a procedure that returns a string
-describing OBJ, and WEIGHT is a positive integer denoting the weight of this
-field in the final score.
+field/weight pairs, where FIELD is a procedure that returns a string or list
+of strings describing OBJ, and WEIGHT is a positive integer denoting the
+weight of this field in the final score.
 
 A score of zero means that OBJ does not match any of REGEXPS.  The higher the
 score, the more relevant OBJ is to REGEXPS."
@@ -1394,8 +1396,10 @@ score, the more relevant OBJ is to REGEXPS."
             ((field . weight)
              (match (field obj)
                (#f  relevance)
-               (str (+ relevance
-                       (* (score str) weight)))))))
+               ((? string? str)
+                (+ relevance (* (score str) weight)))
+               ((lst ...)
+                (+ relevance (* weight (apply + (map score lst)))))))))
         0
         metrics))
 
@@ -1404,6 +1408,15 @@ score, the more relevant OBJ is to REGEXPS."
   ;; of regexps.
   `((,package-name . 4)
 
+    ;; Match against uncommon outputs.
+    (,(lambda (package)
+        (filter (lambda (output)
+                  (not (member output
+                               ;; Some common outpus shared by many packages.
+                               '("out" "doc" "debug" "lib" "include" "bin"))))
+                (package-outputs package)))
+     . 1)
+
     ;; Match regexps on the raw Texinfo since formatting it is quite expensive
     ;; and doesn't have much of an effect on search results.
     (,(lambda (package)

tests/guix-package.sh

@@ -398,3 +398,28 @@ else
     grep "manifest.scm:[1-3]:.*wonderful-package.*: unbound variable" \
 	 "$module_dir/stderr"
 fi
+
+# Verify that package outputs are included in search results.
+rm -rf "$module_dir"
+mkdir "$module_dir"
+cat > "$module_dir/foo.scm"<<EOF
+(define-module (foo)
+  #:use-module (guix packages)
+  #:use-module (guix build-system trivial))
+
+(define-public dummy-package
+  (package
+    (name "dummy-package")
+    (version "dummy-version")
+    (outputs '("out" "dummy-output"))
+    (source #f)
+    ;; Without a real build system, the "guix pacakge -s" command will fail.
+    (build-system trivial-build-system)
+    (synopsis "dummy-synopsis")
+    (description "dummy-description")
+    (home-page "https://dummy-home-page")
+    (license #f)))
+EOF
+guix package -L "$module_dir" -s dummy-output > /tmp/out
+test "`guix package -L "$module_dir" -s dummy-output | grep ^name:`" = "name: dummy-package"
+rm -rf "$module_dir"