build: Add julia-build-system.

* guix/build/julia-build-system.scm: New file.
* guix/build-system/julia.scm: New file.
* Makefile.am (MODULES): Add them.
* doc/guix.texi (Build Systems): Document julia-build-system.

Signed-off-by: Julien Lepiller <julien@lepiller.eu>

Makefile.am

@@ -126,6 +126,7 @@ MODULES =					\
   guix/build-system/gnu.scm			\
   guix/build-system/guile.scm			\
   guix/build-system/haskell.scm			\
+  guix/build-system/julia.scm			\
   guix/build-system/linux-module.scm		\
   guix/build-system/node.scm			\
   guix/build-system/perl.scm			\
@@ -184,6 +185,7 @@ MODULES =					\
   guix/build/texlive-build-system.scm		\
   guix/build/waf-build-system.scm		\
   guix/build/haskell-build-system.scm		\
+  guix/build/julia-build-system.scm		\
   guix/build/linux-module-build-system.scm	\
   guix/build/store-copy.scm			\
   guix/build/json.scm				\

doc/guix.texi

@@ -6034,6 +6034,29 @@ Packages built with @code{guile-build-system} must provide a Guile package in
 their @code{native-inputs} field.
 @end defvr
 
+@defvr {Scheme Variable} julia-build-system
+This variable is exported by @code{(guix build-system julia)}.  It implements
+the build procedure used by @uref{https://julialang.org/, julia} packages,
+which essentially is similar to running @command{julia -e 'using Pkg;
+Pkg.add(package)'} in an environment where @code{JULIA_LOAD_PATH} contains the
+paths to all Julia package inputs.  Tests are run not run.
+
+Julia packages require the source @code{file-name} to be the real name of the
+package, correctly capitalized.
+
+For packages requiring shared library dependencies, you may need to write the
+@file{/deps/deps.jl} file manually. It's usually a line of @code{const
+variable = /gnu/store/libary.so} for each dependency, plus a void function
+@code{check_deps() = nothing}.
+
+Some older packages that aren't using @file{Package.toml} yet, will require
+this file to be created, too. The function @code{julia-create-package-toml}
+helps creating the file. You need to pass the outputs and the source of the
+package, it's name (the same as the @code{file-name} parameter), the package
+uuid, the package version, and a list of dependencies specified by their name
+and their uuid.
+@end defvr
+
 @defvr {Scheme Variable} minify-build-system
 This variable is exported by @code{(guix build-system minify)}.  It
 implements a minification procedure for simple JavaScript packages.

guix/build-system/julia.scm

@@ -0,0 +1,132 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 Nicolò Balzarotti <nicolo@nixo.xyz>
+;;;
+;;; 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 julia)
+  #:use-module ((guix build julia-build-system))
+  #:use-module (gnu packages julia)
+  #:use-module (guix store)
+  #:use-module (guix utils)
+  #:use-module (guix packages)
+  #:use-module (guix derivations)
+  #:use-module (guix search-paths)
+  #:use-module (guix build-system)
+  #:use-module (guix build-system gnu)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-26)
+  #:export (%julia-build-system-modules
+            julia-build
+            julia-build-system))
+
+;; Commentary:
+;;
+;; Standard build procedure for Julia packages.
+;;
+;; Code:
+
+(define %julia-build-system-modules
+  ;; Build-side modules imported by default.
+  `((guix build julia-build-system)
+    ,@%gnu-build-system-modules))
+
+(define (default-julia)
+  "Return the default Julia package."
+  ;; Lazily resolve the binding to avoid a circular dependency.
+  (let ((julia-mod (resolve-interface '(gnu packages julia))))
+    (module-ref julia-mod 'julia)))
+
+(define* (lower name
+                #:key source inputs native-inputs outputs system target
+                (julia julia)
+                #:allow-other-keys
+                #:rest arguments)
+  "Return a bag for NAME."
+  (define private-keywords
+    '(#:target #:julia #:inputs #:native-inputs))
+
+  (and (not target)                        ;XXX: no cross-compilation
+       (bag
+         (name name)
+         (system system)
+         (host-inputs `(,@(if source
+                              `(("source" ,source))
+                              '())
+                        ,@inputs
+                        
+                        ;; Keep the standard inputs of 'gnu-build-system'.
+                        ,@(standard-packages)))
+         (build-inputs `(("julia" ,julia)
+                         ,@native-inputs))
+         (outputs outputs)
+         (build julia-build)
+         (arguments (strip-keyword-arguments private-keywords arguments)))))
+
+(define* (julia-build store name inputs
+                      #:key source
+                      (tests? #f)
+                      (phases '(@ (guix build julia-build-system)
+                                  %standard-phases))
+                      (outputs '("out"))
+                      (search-paths '())
+                      (system (%current-system))
+                      (guile #f)
+                      (imported-modules %julia-build-system-modules)
+                      (modules '((guix build julia-build-system)
+                                 (guix build utils))))
+  "Build SOURCE using Julia, and with INPUTS."
+  (define builder
+    `(begin
+       (use-modules ,@modules)
+       (julia-build #:name ,name
+                    #:source ,(match (assoc-ref inputs "source")
+                                (((? derivation? source))
+                                 (derivation->output-path source))
+                                ((source)
+                                 source)
+                                (source
+                                 source))
+                    #:system ,system
+                    #:tests? ,tests?
+                    #:phases ,phases
+                    #:outputs %outputs
+                    #:search-paths ',(map search-path-specification->sexp
+                                          search-paths)
+                    #:inputs %build-inputs)))
+
+  (define guile-for-build
+    (match guile
+      ((? package?)
+       (package-derivation store guile system #:graft? #f))
+      (#f                                         ; the default
+       (let* ((distro (resolve-interface '(gnu packages commencement)))
+              (guile  (module-ref distro 'guile-final)))
+         (package-derivation store guile system #:graft? #f)))))
+
+  (build-expression->derivation store name builder
+                                #:inputs inputs
+                                #:system system
+                                #:modules imported-modules
+                                #:outputs outputs
+                                #:guile-for-build guile-for-build))
+
+(define julia-build-system
+  (build-system
+   (name 'julia)
+   (description "The build system for Julia packages")
+   (lower lower)))
+
+;;; julia.scm ends here

guix/build/julia-build-system.scm

@@ -0,0 +1,135 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 Nicolò Balzarotti <nicolo@nixo.xyz>
+;;;
+;;; 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 julia-build-system)
+  #:use-module ((guix build gnu-build-system) #:prefix gnu:)
+  #:use-module (guix build utils)
+  #:use-module (ice-9 match)
+  #:export (%standard-phases
+            julia-create-package-toml
+            julia-build))
+
+;; Commentary:
+;;
+;; Builder-side code of the standard build procedure for Julia packages.
+;;
+;; Code:
+
+(define (invoke-julia code)
+  (invoke "julia" "-e" code))
+
+;; subpath where we store the package content
+(define %package-path "/share/julia/packages/")
+
+(define (generate-load-path inputs outputs)
+  (string-append
+   (string-join (map (match-lambda
+                       ((_ . path)
+                        (string-append path %package-path)))
+                     ;; Restrict to inputs beginning with "julia-".
+                     (filter (match-lambda
+                               ((name . _)
+                                (string-prefix? "julia-" name)))
+                             inputs))
+                ":")
+   (string-append ":" (assoc-ref outputs "out") %package-path)
+   ;; stdlib is always required to find Julia's standard libraries.
+   ;; usually there are other two paths in this variable:
+   ;; "@" and "@v#.#"
+   ":@stdlib"))
+
+(define* (install #:key source inputs outputs #:allow-other-keys)
+  (let* ((out (assoc-ref outputs "out"))
+         (package-dir (string-append out %package-path
+                                     (string-append
+                                      (strip-store-file-name source)))))
+    (setenv "JULIA_LOAD_PATH" (generate-load-path inputs outputs))
+    (mkdir-p package-dir)
+    (copy-recursively source package-dir))
+  #t)
+
+;; TODO: Precompilation is working, but I don't know how to tell
+;; julia to use use it. If (on rantime) we set HOME to
+;; store path, julia tries to write files there (failing)
+(define* (precompile #:key source inputs outputs #:allow-other-keys)
+  (let* ((out (assoc-ref outputs "out"))
+         (builddir (string-append out "/share/julia/"))
+         (package (strip-store-file-name source)))
+    (mkdir-p builddir)
+    (setenv "JULIA_DEPOT_PATH" builddir)
+    (setenv "JULIA_LOAD_PATH" (generate-load-path inputs outputs))
+    ;; Actual precompilation
+    (invoke-julia (string-append "using " package)))
+  #t)
+
+(define* (check #:key source inputs outputs #:allow-other-keys)
+  (let* ((out (assoc-ref outputs "out"))
+         (package (strip-store-file-name source))
+         (builddir (string-append out "/share/julia/")))
+    (setenv "JULIA_DEPOT_PATH" builddir)
+    (setenv "JULIA_LOAD_PATH" (generate-load-path inputs outputs))
+    (invoke-julia (string-append "using Pkg;Pkg.test(\"" package "\")")))
+  #t)
+
+(define (julia-create-package-toml outputs source
+                                   name uuid version
+                                   deps)
+  "Some packages are not using the new Package.toml dependency specifications.
+Write this file manually, so that Julia can find its dependencies."
+  (let ((f (open-file
+            (string-append
+             (assoc-ref outputs "out")
+             %package-path
+             (string-append
+              name "/Project.toml"))
+            "w")))
+    (display (string-append
+              "
+name = \"" name "\"
+uuid = \"" uuid "\"
+version = \"" version "\"
+") f)
+    (when (not (null? deps))
+      (display "[deps]\n" f)
+      (for-each (lambda dep
+                  (display (string-append (car (car dep)) " = \"" (cdr (car dep)) "\"\n")
+                           f))
+                deps))
+    (close-port f))
+  #t)
+
+(define %standard-phases
+  (modify-phases gnu:%standard-phases
+    (delete 'check) ; tests must be run after installation
+    (replace 'install install)
+    (add-after 'install 'precompile precompile)
+    ;; (add-after 'install 'check check)
+    ;; TODO: In the future we could add a "system-image-generation" phase
+    ;; where we use PackageCompiler.jl to speed up package loading times
+    (delete 'configure)
+    (delete 'bootstrap)
+    (delete 'patch-usr-bin-file)
+    (delete 'build)))
+
+(define* (julia-build #:key inputs (phases %standard-phases)
+                      #:allow-other-keys #:rest args)
+  "Build the given Julia package, applying all of PHASES in order."
+  (apply gnu:gnu-build
+         #:inputs inputs #:phases phases
+         args))