gnu: Add go-github-com-bep-golibsass.

* gnu/packages/golang.scm: (go-github-com-bep-golibsass): New variable.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/packages/golang.scm

@@ -58,6 +58,7 @@
   #:use-module (gnu packages mp3)
   #:use-module (gnu packages textutils)
   #:use-module (gnu packages tls)
+  #:use-module (gnu packages web)
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-1))
 
@@ -5874,3 +5875,61 @@ additions.")
      "Package quicktest provides a collection of Go helpers for writing
 tests.")
     (license license:expat)))
+
+(define-public go-github-com-bep-golibsass
+  (package
+    (name "go-github-com-bep-golibsass")
+    (version "0.7.0")
+    (source
+     (origin
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/bep/golibsass")
+             (commit (string-append "v" version))))
+       (file-name (git-file-name name version))
+       (sha256
+        (base32
+         "0xk3m2ynbydzx87dz573ihwc4ryq0r545vz937szz175ivgfrhh3"))
+       (modules '((guix build utils)))
+       (snippet
+        '(begin
+           (delete-file-recursively "libsass_src")
+           #t))))
+    (build-system go-build-system)
+    (arguments
+     '(#:import-path "github.com/bep/golibsass/libsass"
+       #:unpack-path "github.com/bep/golibsass"
+       ;; The dev build tag modifies the build to link to system libsass
+       ;; instead of including the bundled one (which we remove.)
+       ;; https://github.com/bep/golibsass/blob/v0.7.0/internal/libsass/a__cgo_dev.go
+       #:build-flags '("-tags" "dev")
+       #:phases
+       (modify-phases %standard-phases
+         (add-before 'build 'generate-bindings
+           ;; Generate bindings for system libsass, replacing the
+           ;; pre-generated bindings.
+           (lambda* (#:key inputs unpack-path #:allow-other-keys)
+             (mkdir-p (string-append "src/" unpack-path "/internal/libsass"))
+             (let ((libsass-src (string-append (assoc-ref inputs "libsass-src") "/src")))
+               (substitute* (string-append "src/" unpack-path "/gen/main.go")
+                 (("filepath.Join\\(rootDir, \"libsass_src\", \"src\"\\)")
+                  (string-append "\"" libsass-src "\""))
+                 (("../../libsass_src/src/")
+                  libsass-src)))
+             (invoke "go" "generate" (string-append unpack-path "/gen"))
+             #t))
+         (replace 'check
+           (lambda* (#:key tests? import-path #:allow-other-keys)
+             (if tests?
+                 (invoke "go" "test" import-path "-tags" "dev"))
+             #t)))))
+    (propagated-inputs
+     `(("libsass" ,libsass)))
+    (native-inputs
+     `(("go-github-com-frankban-quicktest" ,go-github-com-frankban-quicktest)
+       ("libsass-src" ,(package-source libsass))))
+    (home-page "https://github.com/bep/golibsass")
+    (synopsis "Easy to use Go bindings for LibSass")
+    (description
+     "This package provides SCSS compiler support for Go applications.")
+    (license license:expat)))