guix: Add the 'qt' build system.

* guix/build-system/qt.scm, guix/build/qt-build-system.scm: New files.
* Makefile.am (MODULES): Add them.
* doc/guix.texi (Buiild systems): Add the new build system.

Makefile.am

@@ -132,6 +132,7 @@ MODULES =					\
   guix/build-system/perl.scm			\
   guix/build-system/python.scm			\
   guix/build-system/ocaml.scm			\
+  guix/build-system/qt.scm			\
   guix/build-system/waf.scm			\
   guix/build-system/r.scm			\
   guix/build-system/rakudo.scm			\
@@ -178,6 +179,7 @@ MODULES =					\
   guix/build/perl-build-system.scm		\
   guix/build/python-build-system.scm		\
   guix/build/ocaml-build-system.scm		\
+  guix/build/qt-build-system.scm		\
   guix/build/r-build-system.scm			\
   guix/build/rakudo-build-system.scm		\
   guix/build/ruby-build-system.scm		\

doc/guix.texi

@@ -47,7 +47,7 @@ Copyright @copyright{} 2017 Thomas Danckaert@*
 Copyright @copyright{} 2017 humanitiesNerd@*
 Copyright @copyright{} 2017 Christopher Allan Webber@*
 Copyright @copyright{} 2017, 2018 Marius Bakke@*
-Copyright @copyright{} 2017 Hartmut Goebel@*
+Copyright @copyright{} 2017, 2019 Hartmut Goebel@*
 Copyright @copyright{} 2017, 2019 Maxim Cournoyer@*
 Copyright @copyright{} 2017, 2018, 2019 Tobias Geerinckx-Rice@*
 Copyright @copyright{} 2017 George Clemmer@*
@@ -6410,6 +6410,25 @@ passes flags specified by the @code{#:make-maker-flags} or
 Which Perl package is used can be specified with @code{#:perl}.
 @end defvr
 
+@defvr {Scheme Variable} qt-build-system
+This variable is exported by @code{(guix build-system qt)}.  It
+is intended for use with applications using Qt or KDE.
+
+This build system adds the phase @code{qt-wrap} to the ones defined by
+@var{cmake-build-system}, after the @code{install} phase.
+
+This phase searches for Qt5 plugin paths, QML paths and some XDG in the inputs
+and output.  In case some path is found, all programs in the output's
+@file{bin/}, @file{sbin/}, @file{libexec/} and @file{lib/libexec/} directories
+are wrapped in scripts defining the necessary environment variables.
+
+It is possible to exclude specific package outputs from that wrapping process
+by listing their names in the @code{#:qt-wrap-excluded-outputs} parameter.
+This is useful when an output is known not to contain any Qt binaries, and
+where wrapping would gratuitously add a dependency of that output on Qt, KDE,
+or such.
+@end defvr
+
 @defvr {Scheme Variable} r-build-system
 This variable is exported by @code{(guix build-system r)}.  It
 implements the build procedure used by @uref{https://r-project.org, R}

guix/build-system/qt.scm

@@ -0,0 +1,295 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013 Cyril Roelandt <tipecaml@gmail.com>
+;;; Copyright © 2017 Ricardo Wurmus <rekado@elephly.net>
+;;; Copyright © 2019 Hartmut Goebel <h.goebel@crazy-compilers.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 qt)
+  #: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 cmake)
+  #:use-module (guix build-system gnu)
+  #:use-module (guix packages)
+  #:use-module (ice-9 match)
+  #:export (%qt-build-system-modules
+            qt-build
+            qt-build-system))
+
+;; Commentary:
+;;
+;; This build system is an extension of the 'cmake-build-system'.  It
+;; accommodates the needs of Qt and KDE applications by adding a phase run
+;; after the 'install' phase:
+;;
+;; 'qt-wrap' phase:
+;;
+;; This phase looks for Qt5 plugin paths, QML paths and some XDG paths as well
+;; as the corresponding environment variables.  If any of these is found in
+;; the output or if respective environment variables are set, then all
+;; programs in the output's "bin", "sbin", "libexec and "lib/libexec"
+;; directories are wrapped in scripts defining the necessary environment
+;; variables.
+;;
+;; Code:
+
+(define %qt-build-system-modules
+  ;; Build-side modules imported and used by default.
+  `((guix build qt-build-system)
+    ,@%cmake-build-system-modules))
+
+(define (default-cmake)
+  "Return the default CMake package."
+
+  ;; Do not use `@' to avoid introducing circular dependencies.
+  (let ((module (resolve-interface '(gnu packages cmake))))
+    (module-ref module 'cmake-minimal)))
+
+;; This barely is a copy from (guix build-system cmake), only adjusted to use
+;; the variables defined here.
+(define* (lower name
+                #:key source inputs native-inputs outputs system target
+                (cmake (default-cmake))
+                #:allow-other-keys
+                #:rest arguments)
+  "Return a bag for NAME."
+  (define private-keywords
+    `(#:source #:cmake #:inputs #:native-inputs #:outputs
+      ,@(if target '() '(#:target))))
+
+  (bag
+    (name name)
+    (system system)
+    (target target)
+    (build-inputs `(,@(if source
+                          `(("source" ,source))
+                          '())
+                    ,@`(("cmake" ,cmake))
+                    ,@native-inputs
+                    ,@(if target
+                          ;; Use the standard cross inputs of
+                          ;; 'gnu-build-system'.
+                          (standard-cross-packages target 'host)
+                          '())
+                    ;; Keep the standard inputs of 'gnu-build-system'.
+                    ,@(standard-packages)))
+    (host-inputs inputs)
+
+    ;; The cross-libc is really a target package, but for bootstrapping
+    ;; reasons, we can't put it in 'host-inputs'.  Namely, 'cross-gcc' is a
+    ;; native package, so it would end up using a "native" variant of
+    ;; 'cross-libc' (built with 'gnu-build'), whereas all the other packages
+    ;; would use a target variant (built with 'gnu-cross-build'.)
+    (target-inputs (if target
+                       (standard-cross-packages target 'target)
+                       '()))
+    (outputs outputs)
+    (build (if target qt-cross-build qt-build))
+    (arguments (strip-keyword-arguments private-keywords arguments))))
+
+
+(define* (qt-build store name inputs
+                      #:key (guile #f)
+                      (outputs '("out")) (configure-flags ''())
+                      (search-paths '())
+                      (make-flags ''())
+                      (out-of-source? #t)
+                      (build-type "RelWithDebInfo")
+                      (tests? #t)
+                      (test-target "test")
+                      (parallel-build? #t) (parallel-tests? #f)
+                      (validate-runpath? #t)
+                      (patch-shebangs? #t)
+                      (strip-binaries? #t)
+                      (strip-flags ''("--strip-debug"))
+                      (strip-directories ''("lib" "lib64" "libexec"
+                                            "bin" "sbin"))
+                      (phases '(@ (guix build qt-build-system)
+                                  %standard-phases))
+                      (qt-wrap-excluded-outputs ''())
+                      (system (%current-system))
+                      (imported-modules %qt-build-system-modules)
+                      (modules '((guix build cmake-build-system)
+                                 (guix build utils))))
+  "Build SOURCE using CMAKE, and with INPUTS. This assumes that SOURCE
+provides a 'CMakeLists.txt' file as its build system."
+  (define builder
+    `(begin
+       (use-modules ,@modules)
+       (cmake-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
+                    #:qt-wrap-excluded-outputs ,qt-wrap-excluded-outputs
+                    #:configure-flags ,configure-flags
+                    #:make-flags ,make-flags
+                    #:out-of-source? ,out-of-source?
+                    #:build-type ,build-type
+                    #:tests? ,tests?
+                    #:test-target ,test-target
+                    #:parallel-build? ,parallel-build?
+                    #:parallel-tests? ,parallel-tests?
+                    #: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))
+
+
+;;;
+;;; Cross-compilation.
+;;;
+
+(define* (qt-cross-build store name
+                            #:key
+                            target native-drvs target-drvs
+                            (guile #f)
+                            (outputs '("out"))
+                            (configure-flags ''())
+                            (search-paths '())
+                            (native-search-paths '())
+                            (make-flags ''())
+                            (out-of-source? #t)
+                            (build-type "RelWithDebInfo")
+                            (tests? #f) ; nothing can be done
+                            (test-target "test")
+                            (parallel-build? #t) (parallel-tests? #f)
+                            (validate-runpath? #t)
+                            (patch-shebangs? #t)
+                            (strip-binaries? #t)
+                            (strip-flags ''("--strip-debug"
+                                            "--enable-deterministic-archives"))
+                            (strip-directories ''("lib" "lib64" "libexec"
+                                                  "bin" "sbin"))
+                            (phases '(@ (guix build qt-build-system)
+                                     %standard-phases))
+                            (system (%current-system))
+                            (build (nix-system->gnu-triplet system))
+                            (imported-modules %qt-build-system-modules)
+                            (modules '((guix build cmake-build-system)
+                                       (guix build utils))))
+  "Cross-build NAME using CMAKE for TARGET, where TARGET is a GNU triplet and
+with INPUTS.  This assumes that SOURCE provides a 'CMakeLists.txt' file as its
+build system."
+  (define builder
+    `(begin
+       (use-modules ,@modules)
+       (let ()
+         (define %build-host-inputs
+           ',(map (match-lambda
+                    ((name (? derivation? drv) sub ...)
+                     `(,name . ,(apply derivation->output-path drv sub)))
+                    ((name path)
+                     `(,name . ,path)))
+                  native-drvs))
+
+         (define %build-target-inputs
+           ',(map (match-lambda
+                    ((name (? derivation? drv) sub ...)
+                     `(,name . ,(apply derivation->output-path drv sub)))
+                    ((name (? package? pkg) sub ...)
+                     (let ((drv (package-cross-derivation store pkg
+                                                          target system)))
+                       `(,name . ,(apply derivation->output-path drv sub))))
+                    ((name path)
+                     `(,name . ,path)))
+                  target-drvs))
+
+         (cmake-build #:source ,(match (assoc-ref native-drvs "source")
+                                  (((? derivation? source))
+                                   (derivation->output-path source))
+                                  ((source)
+                                   source)
+                                  (source
+                                   source))
+                      #:system ,system
+                      #:build ,build
+                      #:target ,target
+                      #:outputs %outputs
+                      #:inputs %build-target-inputs
+                      #:native-inputs %build-host-inputs
+                      #:search-paths ',(map search-path-specification->sexp
+                                            search-paths)
+                      #:native-search-paths ',(map
+                                               search-path-specification->sexp
+                                               native-search-paths)
+                      #:phases ,phases
+                      #:configure-flags ,configure-flags
+                      #:make-flags ,make-flags
+                      #:out-of-source? ,out-of-source?
+                      #:build-type ,build-type
+                      #:tests? ,tests?
+                      #:test-target ,test-target
+                      #:parallel-build? ,parallel-build?
+                      #:parallel-tests? ,parallel-tests?
+                      #: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 (append native-drvs target-drvs)
+                                #:outputs outputs
+                                #:modules imported-modules
+                                #:guile-for-build guile-for-build))
+
+(define qt-build-system
+  (build-system
+    (name 'qt)
+    (description
+     "The CMake build system augmented with definition of suitable environment
+variables for Qt and KDE in program wrappers.")
+    (lower lower)))

guix/build/qt-build-system.scm

@@ -0,0 +1,109 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2014 Federico Beffa <beffa@fbengineering.ch>
+;;; Copyright © 2014, 2015 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2018 Mark H Weaver <mhw@netris.org>
+;;; Copyright © 2019 Hartmut Goebel <h.goebel@crazy-compilers.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 qt-build-system)
+  #:use-module ((guix build cmake-build-system) #:prefix cmake:)
+  #:use-module (guix build utils)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 regex)
+  #:use-module (ice-9 ftw)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:export (%standard-phases
+            qt-build))
+
+;; Commentary:
+;;
+;; Builder-side code of the standard Qt build procedure.
+;;
+;; Code:
+
+(define (variables-for-wrapping base-directories)
+
+  (define (collect-sub-dirs base-directories subdirectory)
+    (filter-map
+     (lambda (dir)
+       (let ((directory (string-append dir subdirectory)))
+         (if (directory-exists? directory) directory #f)))
+     base-directories))
+
+  (filter
+   (lambda (var-to-wrap) (not (null? (last var-to-wrap))))
+   (map
+    (lambda (var-spec)
+      `(,(first var-spec) = ,(collect-sub-dirs base-directories (last var-spec))))
+    (list
+     ;; these shall match the search-path-specification for Qt and KDE
+     ;; libraries
+     '("XDG_DATA_DIRS" "/share")
+     '("XDG_CONFIG_DIRS" "/etc/xdg")
+     '("QT_PLUGIN_PATH" "/lib/qt5/plugins")
+     '("QML2_IMPORT_PATH" "/lib/qt5/qml")))))
+
+(define* (wrap-all-programs #:key inputs outputs
+                            (qt-wrap-excluded-outputs '())
+                            #:allow-other-keys)
+  "Implement phase \"qt-wrap\": look for GSettings schemas and
+gtk+-v.0 libraries and create wrappers with suitably set environment variables
+if found.
+
+Wrapping is not applied to outputs whose name is listed in
+QT-WRAP-EXCLUDED-OUTPUTS.  This is useful when an output is known not
+to contain any Qt binaries, and where wrapping would gratuitously
+add a dependency of that output on Qt."
+  (define (find-files-to-wrap directory)
+    (append-map
+     (lambda (dir)
+       (if (directory-exists? dir) (find-files dir ".*") (list)))
+     (list (string-append directory "/bin")
+           (string-append directory "/sbin")
+           (string-append directory "/libexec")
+           (string-append directory "/lib/libexec"))))
+
+  (define input-directories
+    ;; FIXME: Filter out unwanted inputs, e.g. cmake
+    (match inputs
+           (((_ . dir) ...)
+            dir)))
+
+  (define handle-output
+    (match-lambda
+     ((output . directory)
+      (unless (member output qt-wrap-excluded-outputs)
+        (let ((bin-list     (find-files-to-wrap directory))
+              (vars-to-wrap (variables-for-wrapping
+                             (append (list output)
+                                         input-directories))))
+          (when (not (null? vars-to-wrap))
+            (for-each (cut apply wrap-program <> vars-to-wrap)
+                      bin-list)))))))
+
+  (for-each handle-output outputs)
+  #t)
+
+(define %standard-phases
+  (modify-phases cmake:%standard-phases
+    (add-after 'install 'qt-wrap wrap-all-programs)))
+
+(define* (qt-build #:key inputs (phases %standard-phases)
+                   #:allow-other-keys #:rest args)
+  "Build the given package, applying all of PHASES in order."
+  (apply cmake:cmake-build #:inputs inputs #:phases phases args))