import: gem: Fix null at home-page.

The RubyGems API returns "homepage_uri": null for gems with no homepage.
guile-json parses JSON null as the Guile symbol 'null', which passes
through into the generated package sexp as (home-page null)—an unbound
variable error at evaluation time.

* tests/import/gem.scm (test-no-homepage-json): New fixture.
  ("gem->guix-package, bald homepage_uri"): New test.
* guix/import/gem.scm (non-empty-string-or-false): New procedure.
  (<gem>)[home-page]: Use it.
* guix/import/utils.scm (non-empty-string-or-false):
  New exported procedure, moved to here...
* guix/import/gem.scm (non-empty-string-or-false): ...from here...
* guix/import/pypi.scm (non-empty-string-or-false): ...and here.

Change-Id: If8f2ca32834d762c753797067ef87937503ff9f9
Reviewed-by: Carlo Zancanaro <carlo@zancanaro.id.au>
Signed-off-by: Nguyễn Gia Phong <cnx@loang.net>

4 files changed, 49 insertions, 7 deletions

diff --git a/guix/import/gem.scm b/guix/import/gem.scm
index 6acea107171..d7a61788462 100644
--- a/guix/import/gem.scm
+++ b/guix/import/gem.scm
@@ -63,7 +63,8 @@
   (info          gem-info)
   (sha256        gem-sha256 "sha"                 ;bytevector
                  base16-string->bytevector)
-  (home-page     gem-home-page "homepage_uri")    ;string
+  (home-page     gem-home-page "homepage_uri"     ;string | #f
+                 non-empty-string-or-false)
   (dependencies  gem-dependencies "dependencies"  ;<gem-dependencies>
                  json->gem-dependencies))
 
diff --git a/guix/import/pypi.scm b/guix/import/pypi.scm
index cb3b90368c0..419662ec87d 100644
--- a/guix/import/pypi.scm
+++ b/guix/import/pypi.scm
@@ -98,12 +98,6 @@
         "pytest-isort" "pytest-flake8" "pytest-cov" "pytest-black" ; variants
         "pytest-pep8" "pytest-mypy" "pytest-pep8" "pre-commit"))   ;
 
-(define non-empty-string-or-false
-  (match-lambda
-    ("" #f)
-    ((? string? str) str)
-    ((or 'null #f) #f)))
-
 ;; PyPI project.
 (define-json-mapping <pypi-project> make-pypi-project pypi-project?
   json->pypi-project
diff --git a/guix/import/utils.scm b/guix/import/utils.scm
index c435981ca99..a9ff90f0ee1 100644
--- a/guix/import/utils.scm
+++ b/guix/import/utils.scm
@@ -97,6 +97,7 @@
             spdx-string->license
             license->symbol
 
+            non-empty-string-or-false
             snake-case
             beautify-description
             beautify-synopsis
@@ -470,6 +471,12 @@ object is bound to in the (guix licenses) module, such as 'license:gpl3+, or
                 (resolve-interface '(guix licenses) #:prefix 'license:)))
   (assoc-ref licenses license))
 
+(define non-empty-string-or-false
+  (match-lambda
+    ("" #f)
+    ((? string? str) str)
+    ((or 'null #f) #f)))
+
 (define (snake-case str)
   "Return a downcased version of the string STR where underscores and periods
 are replaced with dashes."
diff --git a/tests/import/gem.scm b/tests/import/gem.scm
index beee1508756..dfa33d40366 100644
--- a/tests/import/gem.scm
+++ b/tests/import/gem.scm
@@ -112,6 +112,19 @@
   \"licenses\": [\"MIT\"]
 }")
 
+(define test-no-homepage-json
+  "{
+  \"name\": \"no-homepage\",
+  \"version\": \"1.0.0\",
+  \"sha\": \"f3676eafca9987cb5fe263df1edf2538bf6dafc712b30e17be3543a9680547a8\",
+  \"info\": \"A gem with no homepage\",
+  \"homepage_uri\": null,
+  \"dependencies\": {
+    \"runtime\": []
+  },
+  \"licenses\": [\"MIT\"]
+}")
+
 (test-begin "gem")
 
 (test-assert "gem->guix-package"
@@ -306,4 +319,31 @@
           (list (upstream-source-urls source)
                 (upstream-source-inputs source)))))
 
+(test-assert "gem->guix-package, bald homepage_uri"
+  (mock ((guix http-client) http-fetch
+         (lambda (url . rest)
+           (match url
+             ("https://rubygems.org/api/v1/gems/no-homepage.json"
+              (values (open-input-string test-no-homepage-json)
+                      (string-length test-no-homepage-json)))
+             (_ (error "Unexpected URL: " url)))))
+    (match (gem->guix-package "no-homepage")
+      (`(package
+          (name "ruby-no-homepage")
+          (version "1.0.0")
+          (source (origin
+                    (method url-fetch)
+                    (uri (rubygems-uri "no-homepage" version))
+                    (sha256
+                     (base32
+                      "1a270mlajhrmpqbhxcqjqypnvgrq4pgixpv3w9gwp1wrrapnwrzk"))))
+          (build-system ruby-build-system)
+          (synopsis "A gem with no homepage")
+          (description "This package provides a gem with no homepage.")
+          (home-page #f)
+          (license license:expat))
+       #t)
+      (x
+       (pk 'fail x #f)))))
+
 (test-end "gem")