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[bug#55030] [PATCH 03/30] guix: Add elm-build-system and 'guix import el


From: Philip McGrath
Subject: [bug#55030] [PATCH 03/30] guix: Add elm-build-system and 'guix import elm'.
Date: Tue, 19 Apr 2022 19:31:47 -0400

* gnu/packages/patches/elm-offline-package-registry.scm: 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,
guix/import/elm.scm, guix/scripts/import/elm.scm: New files.
* guix/scripts/import.scm (importers): Add "elm".
---
 gnu/local.mk                                  |   1 +
 gnu/packages/elm.scm                          |   8 +-
 .../elm-offline-package-registry.patch        |  71 ++++
 guix/build-system/elm.scm                     | 144 +++++++
 guix/build/elm-build-system.scm               | 380 ++++++++++++++++++
 guix/import/elm.scm                           | 148 +++++++
 guix/scripts/import.scm                       |   3 +-
 guix/scripts/import/elm.scm                   | 107 +++++
 8 files changed, 859 insertions(+), 3 deletions(-)
 create mode 100644 gnu/packages/patches/elm-offline-package-registry.patch
 create mode 100644 guix/build-system/elm.scm
 create mode 100644 guix/build/elm-build-system.scm
 create mode 100644 guix/import/elm.scm
 create mode 100644 guix/scripts/import/elm.scm

diff --git a/gnu/local.mk b/gnu/local.mk
index 2af4d018ba..6f02f0a6fd 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -1024,6 +1024,7 @@ dist_patch_DATA =                                         
\
   %D%/packages/patches/einstein-build.patch                    \
   %D%/packages/patches/elfutils-tests-ptrace.patch             \
   %D%/packages/patches/elixir-path-length.patch                        \
+  %D%/packages/patches/elm-offline-package-registry.patch      \
   %D%/packages/patches/elm-reactor-static-files.patch          \
   %D%/packages/patches/elogind-revert-polkit-detection.patch   \
   %D%/packages/patches/emacs-exec-path.patch                   \
diff --git a/gnu/packages/elm.scm b/gnu/packages/elm.scm
index be2e4ebcbd..22c1db5942 100644
--- a/gnu/packages/elm.scm
+++ b/gnu/packages/elm.scm
@@ -25,6 +25,7 @@ (define-module (gnu packages elm)
   #:use-module (gnu packages haskell-xyz)
   #:use-module (gnu packages haskell-web)
   #:use-module (guix build-system haskell)
+  #:use-module (guix build-system elm)
   #:use-module (guix gexp)
   #:use-module (guix git-download)
   #:use-module ((guix licenses) #:prefix license:)
@@ -37,6 +38,8 @@ (define-module (gnu packages elm)
 ;; also want to be able to enable it once we can build it.  We patch Elm to
 ;; instead look for the files on disk relative to the executable and to have
 ;; `elm reactor` exit with a useful error message if they aren't there.
+(define %reactor-root-base
+  "share/elm/reactor-")
 (define-public elm
   (package
     (name "elm")
@@ -51,13 +54,14 @@ (define-public elm
        (sha256
         (base32 "1rdg3xp3js9xadclk3cdypkscm5wahgsfmm4ldcw3xswzhw6ri8w"))
        (patches
-        (search-patches "elm-reactor-static-files.patch"))))
+        (search-patches "elm-reactor-static-files.patch"
+                        "elm-offline-package-registry.patch"))))
     (build-system haskell-build-system)
     (arguments
      (list
       #:configure-flags
       #~(list (string-append "--ghc-option=-DGUIX_REACTOR_STATIC_REL_ROOT="
-                             "\"../share/elm/reactor-"
+                             "\"../" #$%reactor-root-base
                              #$(package-version this-package)
                              "\""))
       #:phases
diff --git a/gnu/packages/patches/elm-offline-package-registry.patch 
b/gnu/packages/patches/elm-offline-package-registry.patch
new file mode 100644
index 0000000000..761ec69878
--- /dev/null
+++ b/gnu/packages/patches/elm-offline-package-registry.patch
@@ -0,0 +1,71 @@
+From 06563409e6f2b1cca7bc1b27e31efd07a7569da8 Mon Sep 17 00:00:00 2001
+From: Philip McGrath <philip@philipmcgrath.com>
+Date: Thu, 14 Apr 2022 22:41:04 -0400
+Subject: [PATCH] minimal support for offline builds
+
+Normally, Elm performs HTTP requests before building to obtain or
+update its list of all registed packages and their versions.
+This is problematic in the Guix build environment.
+
+This patch causes Elm to check if the `GUIX_ELM_OFFLINE_REGISTRY_FILE`
+is set and, if so, to use the contents of the file it specifies as
+though it were the response from
+https://package.elm-lang.org/all-packages.
+
+This patch does not attempt to add more general support for offline
+builds. In particular, it does not attempt to support incremental
+updates to the package registry cache file. See also discussion at
+https://discourse.elm-lang.org/t/private-package-tool-spec/6779/25.
+---
+ builder/src/Deps/Registry.hs | 25 +++++++++++++++++++++----
+ 1 file changed, 21 insertions(+), 4 deletions(-)
+
+diff --git a/builder/src/Deps/Registry.hs b/builder/src/Deps/Registry.hs
+index 8d7def98..70cf3622 100644
+--- a/builder/src/Deps/Registry.hs
++++ b/builder/src/Deps/Registry.hs
+@@ -18,6 +18,8 @@ import Control.Monad (liftM2)
+ import Data.Binary (Binary, get, put)
+ import qualified Data.List as List
+ import qualified Data.Map.Strict as Map
++import System.Environment as Env
++import qualified Data.ByteString as BS
+ 
+ import qualified Deps.Website as Website
+ import qualified Elm.Package as Pkg
+@@ -190,13 +192,28 @@ getVersions' name (Registry _ versions) =
+ post :: Http.Manager -> String -> D.Decoder x a -> (a -> IO b) -> IO (Either 
Exit.RegistryProblem b)
+ post manager path decoder callback =
+   let
+-    url = Website.route path []
+-  in
+-  Http.post manager url [] Exit.RP_Http $
+-    \body ->
++    mkBodyCallback url body =
+       case D.fromByteString decoder body of
+         Right a -> Right <$> callback a
+         Left _ -> return $ Left $ Exit.RP_Data url body
++    postOnline url cb =
++      Http.post manager url [] Exit.RP_Http cb
++    performPost f url =
++      f url (mkBodyCallback url)
++  in
++    do
++      maybeFile <- Env.lookupEnv "GUIX_ELM_OFFLINE_REGISTRY_FILE"
++      case (path, maybeFile) of
++        ( "/all-packages", Just file ) ->
++          performPost postOffline file
++        ( _, _ ) ->
++          -- don't know how to handle other endpoints yet
++          performPost postOnline (Website.route path [])
++
++postOffline :: String -> (BS.ByteString -> IO a) -> IO a
++postOffline file callback = do
++  body <- BS.readFile file
++  callback body
+ 
+ 
+ 
+-- 
+2.32.0
+
diff --git a/guix/build-system/elm.scm b/guix/build-system/elm.scm
new file mode 100644
index 0000000000..bf77df6519
--- /dev/null
+++ b/guix/build-system/elm.scm
@@ -0,0 +1,144 @@
+;;; 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
+            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 (elm-package-origin name version hash)
+  "Return an origin for the Elm package 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/"; name))
+          (commit version)))
+    (file-name (git-file-name (elm->package-name 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)))
diff --git a/guix/build/elm-build-system.scm b/guix/build/elm-build-system.scm
new file mode 100644
index 0000000000..b47b16973d
--- /dev/null
+++ b/guix/build/elm-build-system.scm
@@ -0,0 +1,380 @@
+;;; 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 elm-build-system)
+  #:use-module ((guix build gnu-build-system) #:prefix gnu:)
+  #:use-module (guix build utils)
+  #:use-module (guix build json)
+  #:use-module (guix build union)
+  #:use-module (ice-9 ftw)
+  #:use-module (ice-9 rdelim)
+  #:use-module (ice-9 regex)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 popen)
+  #:use-module (ice-9 vlist)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-71)
+  #:export (%standard-phases
+            patch-application-dependencies
+            patch-json-string-escapes
+            read-offline-registry->vhash
+            elm-build))
+
+;; COMMENTARY:
+;;
+;; Elm draws a sharp distinction between "projects" with `{"type":"package"}`
+;; vs. `{"type":"application"}` in the "elm.json" file: see
+;; <https://github.com/elm/compiler/blob/master/docs/elm.json/package.md> and
+;; <https://github.com/elm/compiler/blob/master/docs/elm.json/application.md>.
+;; For now, `elm-build-system` is designed for "package"s: packaging
+;; "application"s requires ad-hoc replacements for some phases---but see
+;; `patch-application-dependencies`, which helps to work around a known issue
+;; discussed below.  It would be nice to add more streamlined support for
+;; "application"s one we have more experience building them in Guix.  For
+;; example, we could incorporate the `uglifyjs` advice from
+;; <https://github.com/elm/compiler/blob/master/hints/optimize.md>.
+;;
+;; We want building an Elm "package" to produce:
+;;
+;;   - a "docs.json" file with extracted documentation; and
+;;
+;;   - an "artifacts.dat" file with compilation results for use in building
+;;     "package"s and "application"s.
+;;
+;; Unfortunately, there isn't an entry point to the Elm compiler that builds
+;; those files directly.  Building with `elm make` does something different,
+;; more oriented toward development, testing, and building "application"s.  We
+;; work around this limitation by staging the "package" we're building as
+;; though it were already installed in ELM_HOME, generating a trivial Elm
+;; "application" that depends on the "package", and building the
+;; "application", which causes the files for the "package" to be built.
+;;
+;; Much of the ceremony involved is to avoid using `elm` in ways that would
+;; make it try to do network IO beyond the bare minimum functionality for
+;; which we've patched a replacement into our `elm`.  On the other hand, we
+;; get to take advantage of the very regular structure required of Elm
+;; packages.
+;;
+;; *Known issue:* Elm itself supports multiple versions of "package"s
+;; coexisting simultaneously under ELM_HOME, but we do not support this yet.
+;; Sometimes, parallel versions coexisting causes `elm` to try to write to
+;; built "artifacts.dat" files.  For now, two workarounds are possible:
+;;
+;;  - Use `patch-application-dependencies` to rewrite an "application"'s
+;;    "elm.json" file to refer to the versions of its inputs actually
+;;    packaged in Guix.
+;;
+;;  - Use a Guix package transformation to rewrite your "application"'s
+;;    dependencies recursively, so that only one version of each Elm
+;;    "package" is included in your "application"'s build environment.
+;;
+;; Patching `elm` more extensively---perhaps adding an `elm guix`
+;; subcommand`---might let us address these issues more directly.
+;;
+;; CODE:
+;;
+
+(define %essential-elm-packages
+  ;; elm/json isn't essential in a fundamental sense,
+  ;; but it's required for a {"type":"application"},
+  ;; which we are generating to trigger the build
+  '("elm/core" "elm/json"))
+
+(define* (target-elm-version #:optional elm)
+  "Return the version of ELM or whichever 'elm' is in $PATH.
+Return #false if it cannot be determined."
+  (let* ((pipe (open-pipe* OPEN_READ
+                           (or elm "elm")
+                           "--version"))
+         (line (read-line pipe)))
+    (and (zero? (close-pipe pipe))
+         (string? line)
+         line)))
+
+(define* (prepare-elm-home #:key native-inputs inputs #:allow-other-keys)
+  "Set the ELM_HOME environment variable and populate the indicated directory
+with the union of the Elm \"package\" inputs.  Also, set GUIX_ELM_VERSION to
+the version of the Elm compiler in use."
+  (let* ((elm (search-input-file (or native-inputs inputs) "/bin/elm"))
+         (elm-version (target-elm-version elm)))
+    (setenv "GUIX_ELM_VERSION" elm-version)
+    (mkdir "../elm-home")
+    (with-directory-excursion "../elm-home"
+      (union-build elm-version
+                   (search-path-as-list
+                    (list (string-append "share/elm/" elm-version))
+                    (map cdr inputs))
+                   #:create-all-directories? #t)
+      (setenv "ELM_HOME" (getcwd)))))
+
+(define* (stage #:key native-inputs inputs  #:allow-other-keys)
+  "Extract the installable files from the Elm \"package\" into a staging
+directory and link it into the ELM_HOME tree.  Also, set GUIX_ELM_PKG_NAME and
+GUIX_ELM_PKG_VERSION to the name and version, respectively, of the Elm package
+being built, as defined in its \"elm.json\" file."
+  (let* ((elm-version (getenv "GUIX_ELM_VERSION"))
+         (elm-home (getenv "ELM_HOME"))
+         (info (match (call-with-input-file "elm.json" read-json)
+                 (('@ . alist) alist)))
+         (name (assoc-ref info "name"))
+         (version (assoc-ref info "version"))
+         (rel-dir (string-append elm-version "/packages/" name "/" version))
+         (staged-dir (string-append elm-home "/../staged/" rel-dir)))
+    (setenv "GUIX_ELM_PKG_NAME" name)
+    (setenv "GUIX_ELM_PKG_VERSION" version)
+    (mkdir-p staged-dir)
+    (mkdir-p (string-append elm-home "/" (dirname rel-dir)))
+    (symlink staged-dir
+             (string-append elm-home "/" rel-dir))
+    (copy-recursively "src" (string-append staged-dir "/src"))
+    (install-file "elm.json" staged-dir)
+    (install-file "README.md" staged-dir)
+    (when (file-exists? "LICENSE")
+      (install-file "LICENSE" staged-dir))))
+
+(define (patch-json-string-escapes file)
+  "Work around a bug in the Elm compiler's JSON parser by attempting to
+replace REVERSE-SOLIDUS--SOLIDUS escape sequences in FILE with unescaped
+SOLIDUS characters."
+  ;; https://github.com/elm/compiler/issues/2255
+  (substitute* file
+    (("\\\\/")
+     "/")))
+
+(define (directory-list dir)
+  "Like DIRECTORY-LIST from 'racket/base': lists the contents of DIR, not
+including the special \".\" and \"..\" entries."
+  (scandir dir (lambda (f)
+                 (not (member f '("." ".."))))))
+
+(define* (make-offline-registry-file #:key inputs #:allow-other-keys)
+  "Generate an \"offline-package-registry.json\" file and sets
+GUIX_ELM_OFFLINE_REGISTRY_FILE to its path, cooperating with a patch to `elm`
+to avoid attempting to download a list of all published Elm package names and
+versions from the internet."
+  (let* ((elm-home (getenv "ELM_HOME"))
+         (elm-version (getenv "GUIX_ELM_VERSION"))
+         (registry-file
+          (string-append elm-home "/../offline-package-registry.json"))
+         (registry-alist
+          ;; here, we don't need to look up entries, so we build the
+          ;; alist directly, rather than using a vhash
+          (with-directory-excursion
+              (string-append elm-home "/" elm-version "/packages")
+            (append-map (lambda (org)
+                          (with-directory-excursion org
+                            (map (lambda (repo)
+                                   (cons (string-append org "/" repo)
+                                         (directory-list repo)))
+                                 (directory-list "."))))
+                        (directory-list ".")))))
+    (call-with-output-file registry-file
+      (lambda (out)
+        (write-json `(@ ,@registry-alist) out)))
+    (patch-json-string-escapes registry-file)
+    (setenv "GUIX_ELM_OFFLINE_REGISTRY_FILE" registry-file)))
+
+(define (read-offline-registry->vhash)
+  "Return a vhash mapping Elm \"package\" names to lists of available version
+strings."
+  (alist->vhash
+   (match (call-with-input-file (getenv "GUIX_ELM_OFFLINE_REGISTRY_FILE")
+            read-json)
+     (('@ . alist) alist))))
+
+(define (find-indirect-dependencies registry-vhash root-pkg root-version)
+  "Return the recursive dependencies of ROOT-PKG, an Elm \"package\" name, at
+version ROOT-VERSION as an alist mapping Elm \"package\" names to (single)
+versions.  The resulting alist will not include entries for
+%ESSENTIAL-ELM-PACKAGES or for ROOT-PKG itself.  The REGISTRY-VHASH is used in
+conjunction with the ELM_HOME environment variable to find dependencies."
+  (with-directory-excursion
+      (string-append (getenv "ELM_HOME")
+                     "/" (getenv "GUIX_ELM_VERSION")
+                     "/packages")
+    (define (get-dependencies pkg version acc)
+      (let* ((elm-json-alist
+              (match (call-with-input-file
+                         (string-append pkg "/" version "/elm.json")
+                       read-json)
+                (('@ . alist) alist)))
+             (deps-alist
+              (match (assoc-ref elm-json-alist "dependencies")
+                (('@ . alist) alist)))
+             (deps-names
+              (filter-map (match-lambda
+                            ((name . range)
+                             (and (not (member name %essential-elm-packages))
+                                  name)))
+                          deps-alist)))
+        (fold register-dependency acc deps-names)))
+    (define (register-dependency pkg acc)
+      ;; Using vhash-cons unconditionally would add duplicate entries,
+      ;; which would then cause problems when we must emit JSON.
+      ;; Plus, we can avoid needlessly duplicating work.
+      (if (vhash-assoc pkg acc)
+          acc
+          (match (vhash-assoc pkg registry-vhash)
+            ((_ version . _)
+             ;; in the rare case that multiple versions are present,
+             ;; just picking an arbitrary one seems to work well enough for now
+             (get-dependencies pkg version (vhash-cons pkg version acc))))))
+    (vlist->list
+     (get-dependencies root-pkg root-version vlist-null))))
+
+(define* (patch-application-dependencies #:key inputs #:allow-other-keys)
+  "Rewrites the \"elm.json\" file in the working directory---which must be of
+`\"type\":\"application\"`, not `\"type\":\"package\"`---to refer to the
+dependency versions actually provided via Guix.  The
+GUIX_ELM_OFFLINE_REGISTRY_FILE environment variable is used to find available
+versions."
+  (let* ((registry-vhash (read-offline-registry->vhash))
+         (rewrite-dep-version
+          (match-lambda
+            ((name . _)
+             (cons name (match (vhash-assoc name registry-vhash)
+                          ((_ version) ;; no dot
+                           version))))))
+         (rewrite-direct/indirect
+          (match-lambda
+            ;; a little checking to avoid confusing misuse with "package"
+            ;; project dependencies, which have a different shape
+            (((and key (or "direct" "indirect"))
+              '@ . alist)
+             `(,key @ ,@(map rewrite-dep-version alist)))))
+         (rewrite-json-section
+          (match-lambda
+            (((and key (or "dependencies" "test-dependencies"))
+              '@ . alist)
+             `(,key @ ,@(map rewrite-direct/indirect alist)))
+            ((k . v)
+             (cons k v))))
+         (rewrite-elm-json
+          (match-lambda
+            (('@ . alist)
+             `(@ ,@(map rewrite-json-section alist))))))
+    (with-atomic-file-replacement "elm.json"
+      (lambda (in out)
+        (write-json (rewrite-elm-json (read-json in))
+                    out)))
+    (patch-json-string-escapes "elm.json")))
+
+(define* (configure #:key native-inputs inputs #:allow-other-keys)
+  "Generate a trivial Elm \"application\" with a direct dependency on the Elm
+\"package\" currently being built."
+  (let* ((info (match (call-with-input-file "elm.json" read-json)
+                 (('@ . alist) alist)))
+         (name (getenv "GUIX_ELM_PKG_NAME"))
+         (version (getenv "GUIX_ELM_PKG_VERSION"))
+         (elm-home (getenv "ELM_HOME"))
+         (registry-vhash (read-offline-registry->vhash))
+         (app-dir (string-append elm-home "/../fake-app")))
+    (mkdir-p (string-append app-dir "/src"))
+    (with-directory-excursion app-dir
+      (call-with-output-file "elm.json"
+        (lambda (out)
+          (write-json
+           `(@ ("type" . "application")
+               ("source-directories" "src") ;; intentionally no dot
+               ("elm-version" . ,(getenv "GUIX_ELM_VERSION"))
+               ("dependencies"
+                @ ("direct"
+                   @ ,@(map (lambda (pkg)
+                              (match (vhash-assoc pkg registry-vhash)
+                                ((_ pkg-version . _)
+                                 (cons pkg
+                                       (if (equal? pkg name)
+                                           version
+                                           pkg-version)))))
+                            (if (member name %essential-elm-packages)
+                                %essential-elm-packages
+                                (cons name %essential-elm-packages))))
+                  ("indirect"
+                   @ ,@(if (member name %essential-elm-packages)
+                           '()
+                           (find-indirect-dependencies registry-vhash
+                                                       name
+                                                       version))))
+               ("test-dependencies"
+                @ ("direct" @)
+                  ("indirect" @)))
+           out)))
+      (patch-json-string-escapes  "elm.json")
+      (with-output-to-file "src/Main.elm"
+        ;; the most trivial possible elm program
+        (lambda ()
+          (display "module Main exposing (..)
+main : Program () () ()
+main = Platform.worker
+ { init = \\_ -> ( (), Cmd.none )
+ , update = \\_ -> \\_ -> ( (), Cmd.none )
+ , subscriptions = \\_ -> Sub.none }"))))))
+
+(define* (build #:key native-inputs inputs #:allow-other-keys)
+  "Run `elm make` to build the Elm \"application\" generated by CONFIGURE."
+  (with-directory-excursion (string-append (getenv "ELM_HOME") "/../fake-app")
+    (invoke (search-input-file (or native-inputs inputs) "/bin/elm")
+            "make"
+            "src/Main.elm")))
+
+(define* (check #:key tests? #:allow-other-keys)
+  "Does nothing, because the `elm-test` executable has not yet been packaged
+for Guix."
+  (when tests?
+    (display "elm-test has not yet been packaged for Guix\n")))
+
+(define* (install #:key outputs #:allow-other-keys)
+  "Installs the contents of the directory generated by STAGE, including any
+files added by BUILD, to the Guix package output."
+  (copy-recursively
+   (string-append (getenv "ELM_HOME") "/../staged")
+   (string-append (assoc-ref outputs "out") "/share/elm")))
+
+(define* (validate-compiled #:key outputs #:allow-other-keys)
+  "Checks that the files \"artifacts.dat\" and \"docs.json\" have been
+installed."
+  (let ((base (string-append "/share/elm/"
+                             (getenv "GUIX_ELM_VERSION")
+                             "/packages/"
+                             (getenv "GUIX_ELM_PKG_NAME")
+                             "/"
+                             (getenv "GUIX_ELM_PKG_VERSION")))
+        (expected '("artifacts.dat" "docs.json")))
+    (for-each (lambda (name)
+                (search-input-file outputs (string-append base "/" name)))
+              expected)))
+
+(define %standard-phases
+  (modify-phases gnu:%standard-phases
+    (add-after 'unpack 'prepare-elm-home prepare-elm-home)
+    (delete 'bootstrap)
+    (add-after 'patch-source-shebangs 'stage stage)
+    (add-after 'stage 'make-offline-registry-file make-offline-registry-file)
+    (replace 'configure configure)
+    (delete 'patch-generated-file-shebangs)
+    (replace 'build build)
+    (replace 'check check)
+    (replace 'install install)
+    (add-before 'validate-documentation-location 'validate-compiled
+      validate-compiled)))
+
+(define* (elm-build #:key inputs (phases %standard-phases)
+                    #:allow-other-keys #:rest args)
+  "Builds the given Elm project, applying all of the PHASES in order."
+  (apply gnu:gnu-build #:inputs inputs #:phases phases args))
diff --git a/guix/import/elm.scm b/guix/import/elm.scm
new file mode 100644
index 0000000000..ef0a31207c
--- /dev/null
+++ b/guix/import/elm.scm
@@ -0,0 +1,148 @@
+;;; 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 import elm)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 regex)
+  #:use-module (ice-9 vlist)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-11)
+  #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-34)
+  #:use-module (srfi srfi-35)
+  #:use-module (guix utils)
+  #:use-module (guix base32)
+  #:use-module (guix hash)
+  #:use-module (guix memoization)
+  #:use-module (guix diagnostics)
+  #:use-module (guix i18n)
+  #:use-module ((guix ui) #:select (display-hint))
+  #:use-module ((guix build utils)
+                #:select ((package-name->name+version
+                           . hyphen-package-name->name+version)
+                          find-files
+                          invoke))
+  #:use-module (guix import utils)
+  #:use-module (guix git)
+  #:use-module (guix import json)
+  #:autoload   (gcrypt hash) (hash-algorithm sha256)
+  #:use-module (json)
+  #:use-module (guix packages)
+  #:use-module (guix upstream)
+  #:use-module ((guix licenses) #:prefix license:)
+  #:use-module (guix build-system elm)
+  #:export (elm-recursive-import
+            elm->guix-package))
+
+(define elm-package-registry
+  ;; It is much nicer to fetch this small (< 40 KB gzipped)
+  ;; file once than to do many HTTP requests.
+  (mlambda ()
+    "Fetch the Elm package registry, represented as a vhash mapping package
+names to lists of available versions, sorted from latest to oldest."
+    (let ((url "https://package.elm-lang.org/all-packages";))
+      (cond
+       ((json-fetch url)
+        => (lambda (alist)
+             (fold (lambda (entry vh)
+                     (match entry
+                       ((name . vec)
+                        (vhash-cons name
+                                    (sort (vector->list vec) version>?)
+                                    vh))))
+                   vlist-null
+                   alist)))
+       (else
+        (raise (formatted-message
+                (G_ "error downloading Elm package registry from ~a")
+                url)))))))
+
+(define (make-elm-package-sexp name version)
+  "Return two values: the `package' s-expression for the Elm package with the
+given NAME and VERSION, and a list of Elm packages it depends on."
+  (define-values (checkout _commit _relation)
+    ;; Elm requires that packages use this very specific format
+    (update-cached-checkout (string-append "https://github.com/"; name)
+                            #:ref `(tag . ,version)))
+  (define info
+    (call-with-input-file (string-append checkout "/elm.json")
+      json->scm))
+  (define (get-deps key)
+    (cond
+     ((assoc-ref info key)
+      => (cut map car <>))
+     (else
+      '())))
+  (define dependencies
+    (get-deps "dependencies"))
+  (define test-dependencies
+    (get-deps "test-dependencies"))
+  (values
+   `(package
+      (name ,(elm->package-name name))
+      (version ,version)
+      (source (elm-package-origin
+               ,name
+               version ;; no ,
+               (base32
+                ,(bytevector->nix-base32-string
+                  (file-hash* checkout
+                              #:algorithm (hash-algorithm sha256)
+                              #:recursive? #t)))))
+      (build-system elm-build-system)
+      ,@(maybe-propagated-inputs (map elm->package-name dependencies))
+      ,@(maybe-inputs (map elm->package-name test-dependencies))
+      (home-page ,(string-append "https://package.elm-lang.org/packages/";
+                                 name "/" version))
+      (synopsis ,(assoc-ref info "summary"))
+      (description
+       ;; Try to use the first paragraph of README.md (which Elm requires),
+       ;; or fall back to summary otherwise.
+       ,(beautify-description
+         (match (chunk-lines (call-with-input-file
+                                 (string-append checkout "/README.md")
+                               read-lines))
+           ((_ par . _)
+            (string-join par " "))
+           (_
+            (assoc-ref info "summary")))))
+      (license ,(spdx-string->license (assoc-ref info "license")))
+      ;; so we know where the "/" goes
+      (properties '((upstream-name . ,name))))
+   (append dependencies test-dependencies)))
+
+(define elm->guix-package
+  (memoize
+   (lambda* (package-name #:key repo version)
+     "Fetch the metadata for PACKAGE-NAME, an Elm package registered at
+package.elm.org, and return two values: the `package' s-expression
+corresponding to that package (or #f on failure) and a list of Elm
+dependencies.."
+     (cond
+      ((vhash-assoc package-name (elm-package-registry))
+       => (match-lambda
+            ((_found latest . _versions)
+             (make-elm-package-sexp package-name (or version latest)))))
+      (else
+       (values #f '()))))))
+
+(define* (elm-recursive-import package-name #:optional version)
+  (recursive-import package-name
+                    #:version version
+                    #:repo->guix-package elm->guix-package
+                    #:guix-name elm->package-name))
diff --git a/guix/scripts/import.scm b/guix/scripts/import.scm
index 40fa6759ae..fa79f3211e 100644
--- a/guix/scripts/import.scm
+++ b/guix/scripts/import.scm
@@ -5,6 +5,7 @@
 ;;; Copyright © 2019 Ricardo Wurmus <rekado@elephly.net>
 ;;; Copyright © 2021 Simon Tournier <zimon.toutoune@gmail.com>
 ;;; Copyright © 2021 Xinglu Chen <public@yoctocell.xyz>
+;;; Copyright © 2022 Philip McGrath <philip@philipmcgrath.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -80,7 +81,7 @@ (define %standard-import-options '())
 
 (define importers '("gnu" "pypi" "cpan" "hackage" "stackage" "egg" "elpa"
                     "gem" "go" "cran" "crate" "texlive" "json" "opam"
-                    "minetest"))
+                    "minetest" "elm"))
 
 (define (resolve-importer name)
   (let ((module (resolve-interface
diff --git a/guix/scripts/import/elm.scm b/guix/scripts/import/elm.scm
new file mode 100644
index 0000000000..68dcbf1070
--- /dev/null
+++ b/guix/scripts/import/elm.scm
@@ -0,0 +1,107 @@
+;;; 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 scripts import elm)
+  #:use-module (guix ui)
+  #:use-module (guix utils)
+  #:use-module (guix scripts)
+  #:use-module (guix import elm)
+  #:use-module (guix scripts import)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-11)
+  #:use-module (srfi srfi-37)
+  #:use-module (srfi srfi-71)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 format)
+  #:export (guix-import-elm))
+
+
+;;;
+;;; Command-line options.
+;;;
+
+(define %default-options
+  '())
+
+(define (show-help)
+  (display (G_ "Usage: guix import elm PACKAGE-NAME
+
+Import and convert the Elm package PACKAGE-NAME.  Optionally, a version
+can be specified after the arobas (@) character.\n"))
+  (display (G_ "
+  -h, --help             display this help and exit"))
+  (display (G_ "
+  -r, --recursive        import packages recursively"))
+  (display (G_ "
+  -V, --version          display version information and exit"))
+  (newline)
+  (show-bug-report-information))
+
+(define %options
+  ;; Specification of the command-line options.
+  (cons* (option '(#\h "help") #f #f
+                 (lambda args
+                   (show-help)
+                   (exit 0)))
+         (option '(#\V "version") #f #f
+                 (lambda args
+                   (show-version-and-exit "guix import elm")))
+         (option '(#\r "recursive") #f #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'recursive #t result)))
+         %standard-import-options))
+
+
+;;;
+;;; Entry point.
+;;;
+
+(define (guix-import-elm . args)
+  (define (parse-options)
+    ;; Return the alist of option values.
+    (parse-command-line args %options (list %default-options)
+                        #:build-options? #f))
+
+  (let* ((opts (parse-options))
+         (args (filter-map (match-lambda
+                             (('argument . value)
+                              value)
+                             (_ #f))
+                           (reverse opts))))
+    (match args
+      ((spec)
+       (with-error-handling
+         (let ((name version (package-name->name+version spec)))
+           (if (assoc-ref opts 'recursive)
+               ;; Recursive import
+               (map (match-lambda
+                      ((and ('package ('name name) . rest) pkg)
+                       `(define-public ,(string->symbol name)
+                          ,pkg))
+                      (_ #f))
+                    (elm-recursive-import name version))
+               ;; Single import
+               (let ((sexp (elm->guix-package name #:version version)))
+                 (unless sexp
+                   (leave (G_ "failed to download meta-data for package 
'~a'~%")
+                          name))
+                 sexp)))))
+      (()
+       (leave (G_ "too few arguments~%")))
+      ((many ...)
+       (leave (G_ "too many arguments~%"))))))
-- 
2.32.0






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