guix: Add elm-build-system.

* gnu/packages/patches/elm-offline-package-registry.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/elm.scm (elm): Use it.
* guix/build-system/elm.scm, guix/build/elm-build-system.scm,
tests/elm.scm: New files.
* Makefile.scm (MODULES, SCM_TESTS): Add them.
* doc/guix.texi (Build Systems): Document 'elm-build-system'.
* doc/contributing.texi (Elm Packages): New section. Document naming
conventions and utilities.

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

1 files changed, 172 insertions, 0 deletions

diff --git a/guix/build-system/elm.scm b/guix/build-system/elm.scm
new file mode 100644
index 0000000000..b54954bf4e
--- /dev/null
+++ b/guix/build-system/elm.scm
@@ -0,0 +1,172 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2022 Philip McGrath <philip@philipmcgrath.com>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix build-system elm)
+  #:use-module (guix store)
+  #:use-module (guix utils)
+  #:use-module (guix packages)
+  #:use-module (guix gexp)
+  #:use-module (guix monads)
+  #:use-module (guix search-paths)
+  #:use-module (guix git-download)
+  #:use-module (guix build-system)
+  #:use-module (guix build-system gnu)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
+  #:export (elm->package-name
+            guix-package->elm-name
+            infer-elm-package-name
+            elm-package-origin
+            %elm-build-system-modules
+            %elm-default-modules
+            elm-build
+            elm-build-system))
+
+(define (elm->package-name name)
+  "Given the NAME of an Elm package, return a Guix-style package name."
+  (let ((converted
+         (string-join (string-split (string-downcase name) #\/) "-")))
+    (if (string-prefix? "elm-" converted)
+        converted
+        (string-append "elm-" converted))))
+
+(define (guix-package->elm-name package)
+  "Given an Elm PACKAGE, return the possibly-inferred upstream name, or #f the
+upstream name is not specified and can't be inferred."
+  (or (assoc-ref (package-properties package) 'upstream-name)
+      (infer-elm-package-name (package-name package))))
+
+(define (infer-elm-package-name guix-name)
+  "Given the GUIX-NAME of an Elm package, return the inferred upstream name,
+or #f if it can't be inferred.  If the result is not #f, supplying it to
+'elm->package-name' would produce GUIX-NAME.
+
+See also 'guix-package->elm-name', which respects the 'upstream-name'
+property."
+  (define (parts-join part0 parts)
+    (string-join (cons part0 parts) "-"))
+  (match (string-split guix-name #\-)
+    (("elm" "explorations" part0 parts ...)
+     (string-append "elm-explorations/"
+                    (parts-join part0 parts)))
+    (("elm" owner part0 parts ...)
+     (string-append owner "/" (parts-join part0 parts)))
+    (("elm" repo)
+     (string-append "elm/" repo))
+    (_
+     #f)))
+
+(define (elm-package-origin elm-name version hash)
+  "Return an origin for the Elm package with upstream name ELM-NAME at the
+given VERSION with sha256 checksum HASH."
+  ;; elm requires this very specific repository structure and tagging regime
+  (origin
+    (method git-fetch)
+    (uri (git-reference
+          (url (string-append "https://github.com/" elm-name))
+          (commit version)))
+    (file-name (git-file-name (elm->package-name elm-name) version))
+    (sha256 hash)))
+
+(define %elm-build-system-modules
+  ;; Build-side modules imported by default.
+  `((guix build elm-build-system)
+    (guix build json)
+    (guix build union)
+    ,@%gnu-build-system-modules))
+
+(define %elm-default-modules
+  ;; Modules in scope in the build-side environment.
+  '((guix build elm-build-system)
+    (guix build utils)
+    (guix build json)
+    (guix build union)))
+
+(define (default-elm)
+  "Return the default Elm package for builds."
+  ;; Lazily resolve the binding to avoid a circular dependency.
+  (let ((elm (resolve-interface '(gnu packages elm))))
+    (module-ref elm 'elm)))
+
+(define* (lower name
+                #:key source inputs native-inputs outputs system target
+                (implicit-elm-package-inputs? #t)
+                (elm (default-elm))
+                #:allow-other-keys
+                #:rest arguments)
+  "Return a bag for NAME."
+  (define private-keywords
+    '(#:target #:implicit-elm-package-inputs? #:elm #:inputs #:native-inputs))
+  (cond
+   (target
+    ;; Cross-compilation is not yet supported.  It should be easy, though,
+    ;; since the build products are all platform-independent.
+    #f)
+   (else
+    (bag
+      (name name)
+      (system system)
+      (host-inputs
+       `(,@(if source
+               `(("source" ,source))
+               '())
+         ,@inputs
+         ("elm" ,elm)
+         ;; TODO: probably don't need most of (standard-packages)
+         ,@(standard-packages)))
+      (outputs outputs)
+      (build elm-build)
+      (arguments (strip-keyword-arguments private-keywords arguments))))))
+
+(define* (elm-build name inputs
+                    #:key
+                    source
+                    (tests? #t)
+                    (phases '%standard-phases)
+                    (outputs '("out"))
+                    (search-paths '())
+                    (system (%current-system))
+                    (guile #f)
+                    (imported-modules %elm-build-system-modules)
+                    (modules %elm-default-modules))
+  "Build SOURCE using ELM."
+  (define builder
+    (with-imported-modules imported-modules
+      #~(begin
+          (use-modules #$@(sexp->gexp modules))
+          (elm-build #:name #$name
+                     #:source #+source
+                     #:system #$system
+                     #:tests? #$tests?
+                     #:phases #$phases
+                     #:outputs #$(outputs->gexp outputs)
+                     #:search-paths '#$(sexp->gexp
+                                        (map search-path-specification->sexp
+                                             search-paths))
+                     #:inputs #$(input-tuples->gexp inputs)))))
+  (mlet %store-monad ((guile (package->derivation (or guile (default-guile))
+                                                  system #:graft? #f)))
+    (gexp->derivation name builder
+                      #:system system
+                      #:guile-for-build guile)))
+
+(define elm-build-system
+  (build-system
+    (name 'elm)
+    (description "The Elm build system")
+    (lower lower)))