guix: Add maven-build-system.

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

Makefile.am

@@ -132,6 +132,7 @@ MODULES =					\
   guix/build-system/haskell.scm			\
   guix/build-system/julia.scm			\
   guix/build-system/linux-module.scm		\
+  guix/build-system/maven.scm			\
   guix/build-system/node.scm			\
   guix/build-system/perl.scm			\
   guix/build-system/python.scm			\
@@ -181,6 +182,7 @@ MODULES =					\
   guix/build/gnu-build-system.scm		\
   guix/build/gnu-dist.scm			\
   guix/build/guile-build-system.scm		\
+  guix/build/maven-build-system.scm		\
   guix/build/node-build-system.scm		\
   guix/build/perl-build-system.scm		\
   guix/build/python-build-system.scm		\

doc/guix.texi

@@ -6811,6 +6811,48 @@ uuid, the package version, and a list of dependencies specified by their name
 and their uuid.
 @end defvr
 
+@defvr {Scheme Variable} maven-build-system
+This variable is exported by @code{(guix build-system maven)}.  It implements
+a build procedure for @uref{https://maven.apache.org, Maven} packages.  Maven
+is a dependency and lifecycle management tool for Java.  A user of Maven
+specifies dependencies and plugins in a @file{pom.xml} file that Maven reads.
+When Maven does not have one of the dependencies or plugins in its repository,
+it will download them and use them to build the package.
+
+The maven build system ensures that maven will not try to download any
+dependency by running in offline mode.  Maven will fail if a dependency is
+missing.  Before running Maven, the @file{pom.xml} (and subprojects) are
+modified to specify the version of dependencies and plugins that match the
+versions available in the guix build environment.  Dependencies and plugins
+must be installed in the fake maven repository at @file{lib/m2}, and are
+symlinked into a proper repository before maven is run.  Maven is instructed
+to use that repository for the build and installs built artifacts there.
+Changed files are copied to the @file{lib/m2} directory of the package output.
+
+You can specify a @file{pom.xml} file with the @code{#:pom-file} argument,
+or let the build system use the default @file{pom.xml} file in the sources.
+
+In case you need to specify a dependency's version manually, you can use the
+@code{#:local-packages} argument.  It takes an association list where the key
+is the groupId of the package and its value is an association list where the
+key is the artifactId of the package and its value is the version you want to
+override in the @file{pom.xml}.
+
+Some packages use dependencies or plugins that are not useful at runtime nor
+at build time in Guix.  You can alter the @file{pom.xml} file to remove them
+using the @code{#:exclude} argument.  Its value is an association list where
+the key is the groupId of the plugin or dependency you want to remove, and
+the value is a list of artifactId you want to remove.
+
+You can override the default @code{jdk} and @code{maven} packages with the
+corresponding argument, @code{#:jdk} and @code{#:maven}.
+
+The @code{#:maven-plugins} argument is a list of maven plugins used during
+the build, with the same format as the @code{inputs} fields of the package
+declaration.  Its default value is @code{%default-maven-plugins} which is
+also exported.
+@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/maven.scm

@@ -0,0 +1,214 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2020 Julien Lepiller <julien@lepiller.eu>
+;;;
+;;; 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 maven)
+  #:use-module (guix store)
+  #:use-module (guix utils)
+  #:use-module (guix derivations)
+  #:use-module (guix search-paths)
+  #:use-module (guix build-system)
+  #:use-module (guix build-system gnu)
+  #:use-module (guix packages)
+  #:use-module (ice-9 match)
+  #:use-module (srfi srfi-1)
+  #:export (%maven-build-system-modules
+            default-maven
+            %default-maven-plugins
+            %default-exclude
+            lower
+            maven-build
+            maven-build-system))
+
+;; Commentary:
+;;
+;; Standard build procedure for Maven packages.  This is implemented as an
+;; extension of `gnu-build-system'.
+;;
+;; Code:
+
+(define %maven-build-system-modules
+  ;; Build-side modules imported by default.
+  `((guix build maven-build-system)
+    (guix build maven pom)
+    ,@%gnu-build-system-modules))
+
+(define (default-maven)
+  "Return the default maven package."
+
+  ;; Do not use `@' to avoid introducing circular dependencies.
+  (let ((module (resolve-interface '(gnu packages maven))))
+    (module-ref module 'maven)))
+
+(define (default-maven-compiler-plugin)
+  "Return the default maven compiler plugin package."
+  ;; Do not use `@' to avoid introducing circular dependencies.
+  (let ((module (resolve-interface '(gnu packages maven))))
+    (module-ref module 'maven-compiler-plugin)))
+
+(define (default-maven-jar-plugin)
+  "Return the default maven jar plugin package."
+  ;; Do not use `@' to avoid introducing circular dependencies.
+  (let ((module (resolve-interface '(gnu packages maven))))
+    (module-ref module 'maven-jar-plugin)))
+
+(define (default-maven-resources-plugin)
+  "Return the default maven resources plugin package."
+  ;; Do not use `@' to avoid introducing circular dependencies.
+  (let ((module (resolve-interface '(gnu packages maven))))
+    (module-ref module 'maven-resources-plugin)))
+
+(define (default-maven-surefire-plugin)
+  "Return the default maven surefire plugin package."
+  ;; Do not use `@' to avoid introducing circular dependencies.
+  (let ((module (resolve-interface '(gnu packages maven))))
+    (module-ref module 'maven-surefire-plugin)))
+
+(define (default-java-surefire-junit4)
+  "Return the default surefire junit4 provider package."
+  ;; Do not use `@' to avoid introducing circular dependencies.
+  (let ((module (resolve-interface '(gnu packages maven))))
+    (module-ref module 'java-surefire-junit4)))
+
+(define (default-maven-install-plugin)
+  "Return the default maven install plugin package."
+  ;; Do not use `@' to avoid introducing circular dependencies.
+  (let ((module (resolve-interface '(gnu packages maven))))
+    (module-ref module 'maven-install-plugin)))
+
+(define (default-jdk)
+  "Return the default JDK package."
+  ;; Lazily resolve the binding to avoid a circular dependency.
+  (let ((jdk-mod (resolve-interface '(gnu packages java))))
+    (module-ref jdk-mod 'icedtea)))
+
+(define %default-maven-plugins
+  `(("maven-compiler-plugin" ,(default-maven-compiler-plugin))
+    ("maven-jar-plugin" ,(default-maven-jar-plugin))
+    ("maven-resources-plugin" ,(default-maven-resources-plugin))
+    ("maven-surefire-plugin" ,(default-maven-surefire-plugin))
+    ("java-surefire-junit4" ,(default-java-surefire-junit4))
+    ("maven-install-plugin" ,(default-maven-install-plugin))))
+
+(define %default-exclude
+  `(("org.apache.maven.plugins" .
+      ("maven-release-plugin" "maven-site-plugin"))))
+
+(define* (lower name
+                #:key source inputs native-inputs outputs system target
+                (maven (default-maven))
+                (jdk (default-jdk))
+                (maven-plugins %default-maven-plugins)
+                (local-packages '())
+                (exclude %default-exclude)
+                #:allow-other-keys
+                #:rest arguments)
+  "Return a bag for NAME."
+  (define private-keywords
+    '(#:source #:target #:jdk #:maven #:maven-plugins #: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 `(("maven" ,maven)
+                         ("jdk" ,jdk "jdk")
+                         ,@maven-plugins
+                         ,@native-inputs))
+         (outputs outputs)
+         (build maven-build)
+         (arguments (strip-keyword-arguments private-keywords arguments)))))
+
+(define* (maven-build store name inputs
+                       #:key (guile #f)
+                       (outputs '("out"))
+                       (search-paths '())
+                       (out-of-source? #t)
+                       (validate-runpath? #t)
+                       (patch-shebangs? #t)
+                       (strip-binaries? #t)
+                       (exclude %default-exclude)
+                       (local-packages '())
+                       (tests? #t)
+                       (strip-flags ''("--strip-debug"))
+                       (strip-directories ''("lib" "lib64" "libexec"
+                                             "bin" "sbin"))
+                       (phases '(@ (guix build maven-build-system)
+                                   %standard-phases))
+                       (system (%current-system))
+                       (imported-modules %maven-build-system-modules)
+                       (modules '((guix build maven-build-system)
+                                  (guix build maven pom)
+                                  (guix build utils))))
+  "Build SOURCE using PATCHELF, and with INPUTS. This assumes that SOURCE
+provides its own binaries."
+  (define builder
+    `(begin
+       (use-modules ,@modules)
+       (maven-build #:source ,(match (assoc-ref inputs "source")
+                                 (((? derivation? source))
+                                  (derivation->output-path source))
+                                 ((source)
+                                  source)
+                                 (source
+                                  source))
+                     #:system ,system
+                     #:outputs %outputs
+                     #:inputs %build-inputs
+                     #:search-paths ',(map search-path-specification->sexp
+                                           search-paths)
+                     #:phases ,phases
+                     #:exclude (quote ,exclude)
+                     #:local-packages (quote ,local-packages)
+                     #:tests? ,tests?
+                     #:out-of-source? ,out-of-source?
+                     #:validate-runpath? ,validate-runpath?
+                     #:patch-shebangs? ,patch-shebangs?
+                     #:strip-binaries? ,strip-binaries?
+                     #:strip-flags ,strip-flags
+                     #:strip-directories ,strip-directories)))
+
+  (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
+                                #:system system
+                                #:inputs inputs
+                                #:modules imported-modules
+                                #:outputs outputs
+                                #:guile-for-build guile-for-build))
+
+(define maven-build-system
+  (build-system
+    (name 'maven)
+    (description "The standard Maven build system")
+    (lower lower)))
+
+;;; maven.scm ends here

guix/build/maven-build-system.scm

@@ -0,0 +1,163 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2020 Julien Lepiller <julien@lepiller.eu>
+;;;
+;;; 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 maven-build-system)
+  #:use-module ((guix build gnu-build-system) #:prefix gnu:)
+  #:use-module (guix build utils)
+  #:use-module (guix build maven pom)
+  #:use-module (ice-9 match)
+  #:export (%standard-phases
+            maven-build))
+
+;; Commentary:
+;;
+;; Builder-side code of the standard maven build procedure.
+;;
+;; Code:
+
+(define* (set-home #:key outputs inputs #:allow-other-keys)
+  (let ((home (string-append (getcwd) "/build-home")))
+    (setenv "HOME" home))
+  (setenv "JAVA_HOME" (assoc-ref inputs "jdk"))
+  #t)
+
+(define* (configure #:key inputs #:allow-other-keys)
+  (let* ((m2-files (map
+                     (lambda (input)
+                       (match input
+                         ((name . dir)
+                          (let ((m2-dir (string-append dir "/lib/m2")))
+                            (if (file-exists? m2-dir) m2-dir #f)))))
+                     inputs))
+         (m2-files (filter (lambda (a) a) m2-files)))
+    (for-each
+      (lambda (m2-dir)
+        (for-each
+          (lambda (file)
+            (let ((dir (string-append (getenv "HOME") "/.m2/repository/"
+                                      (dirname file))))
+              (mkdir-p dir)
+              (symlink (string-append m2-dir "/" file)
+                       (string-append dir "/" (basename file)))))
+          (with-directory-excursion m2-dir
+            (find-files "." ".*.(jar|pom)$"))))
+      m2-files))
+  (invoke "mvn" "-v")
+  #t)
+
+(define (add-local-package local-packages group artifact version)
+  (define (alist-set lst key val)
+    (match lst
+      ('() (list (cons key val)))
+      (((k . v) lst ...)
+       (if (equal? k key)
+         (cons (cons key val) lst)
+         (cons (cons k v) (alist-set lst key val))))))
+  (alist-set local-packages group
+    (alist-set (or (assoc-ref local-packages group) '()) artifact
+      version)))
+
+(define (fix-pom pom-file inputs local-packages excludes)
+  (chmod pom-file #o644)
+  (format #t "fixing ~a~%" pom-file)
+  (fix-pom-dependencies pom-file (map cdr inputs)
+                        #:with-plugins? #t #:with-build-dependencies? #t
+                        #:local-packages local-packages
+                        #:excludes excludes)
+  (let* ((pom (get-pom pom-file))
+         (java-inputs (map cdr inputs))
+         (artifact (pom-artifactid pom))
+         (group (pom-groupid pom java-inputs local-packages))
+         (version (pom-version pom java-inputs local-packages)))
+    (let loop ((modules (pom-ref pom "modules"))
+               (local-packages
+                 (add-local-package local-packages group artifact version)))
+      (pk 'local-packages local-packages)
+      (match modules
+        (#f local-packages)
+        ('() local-packages)
+        (((? string? _) modules ...)
+         (loop modules local-packages))
+        (((_ module) modules ...)
+         (loop
+           modules
+           (fix-pom (string-append (dirname pom-file) "/" module "/pom.xml")
+                    inputs local-packages excludes)))))))
+
+(define* (fix-pom-files #:key inputs local-packages exclude #:allow-other-keys)
+  (fix-pom "pom.xml" inputs local-packages exclude))
+
+(define* (build #:key outputs #:allow-other-keys)
+  "Build the given package."
+  (invoke "mvn" "package"
+          ;; offline mode: don't download dependencies
+          "-o"
+          ;, set directory where dependencies are installed
+          (string-append "-Duser.home=" (getenv "HOME")))
+  #t)
+
+(define* (check #:key tests? #:allow-other-keys)
+  "Check the given package."
+  (when tests?
+    (invoke "mvn" "test"
+            (string-append "-Duser.home=" (getenv "HOME"))
+            "-e"))
+  #t)
+
+(define* (install #:key outputs #:allow-other-keys)
+  "Install the given package."
+  (let* ((out (assoc-ref outputs "out"))
+         (java (string-append out "/lib/m2")))
+    (invoke "mvn" "install" "-o" "-e"
+            "-DskipTests"
+            (string-append "-Duser.home=" (getenv "HOME")))
+    ;; Go through the repository to find files that can be installed
+    (with-directory-excursion (string-append (getenv "HOME") "/.m2/repository")
+      (let ((installable
+              (filter (lambda (file)
+                        (not (eq? 'symlink (stat:type (lstat file)))))
+                      (find-files "." "."))))
+        (mkdir-p java)
+        (for-each
+          (lambda (file)
+            (mkdir-p (string-append java "/" (dirname file)))
+            (copy-file file (string-append java "/" file)))
+          installable)))
+    ;; Remove some files that are not required and introduce timestamps
+    (for-each delete-file (find-files out "maven-metadata-local.xml"))
+    (for-each delete-file (find-files out "_remote.repositories")))
+  #t)
+
+(define %standard-phases
+  ;; Everything is as with the GNU Build System except for the `configure'
+  ;; , `build', `check' and `install' phases.
+  (modify-phases gnu:%standard-phases
+    (delete 'bootstrap)
+    (add-before 'configure 'set-home set-home)
+    (replace 'configure configure)
+    (add-after 'configure 'fix-pom-files fix-pom-files)
+    (replace 'build build)
+    (replace 'check check)
+    (replace 'install install)))
+
+(define* (maven-build #:key inputs (phases %standard-phases)
+                      #:allow-other-keys #:rest args)
+  "Build the given package, applying all of PHASES in order."
+  (apply gnu:gnu-build #:inputs inputs #:phases phases args))
+
+;;; maven-build-system.scm ends here