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+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 Julien Lepiller <julien@lepiller.eu>
+;;; Copyright © 2020 Pierre Neidhardt <mail@ambrevar.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 copy-build-system)
+  #:use-module ((guix build gnu-build-system) #:prefix gnu:)
+  #:use-module (guix build utils)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 ftw)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:export (%standard-phases
+            copy-build))
+
+;; Commentary:
+;;
+;; System for building packages that don't require much compilation, mostly
+;; only to copy files around.
+;;
+;; Code:
+
+(define* (install #:key install-plan outputs #:allow-other-keys)
+  "Copy files from the \"source\" build input to the \"out\" output according to INSTALL-PLAN.
+
+An install plan is a list of plans in the form:
+
+  (SOURCE TARGET [FILTERS])
+
+In the above, FILTERS are optional.
+
+- When SOURCE matches a file or directory without trailing slash, install it to
+  TARGET.
+  - If TARGET has a trailing slash, install SOURCE basename beneath TARGET.
+  - Otherwise install SOURCE as TARGET.
+
+- When SOURCE is a directory with a trailing slash, or when FILTERS are used,
+  the trailing slash of TARGET is implied.
+  - Without FILTERS, install the full SOURCE _content_ to TARGET.
+    The paths relative to SOURCE are preserved within TARGET.
+  - With FILTERS among `#:include`, `#:include-regexp`, `#:exclude`,
+    `#:exclude-regexp`:
+    - With `#:include`, install only the paths which suffix exactly matches
+      one of the elements in the list.
+    - With `#:include-regexp`, install subpaths matching the regexps in the list.
+    - The `#:exclude*` FILTERS work similarly.  Without `#:include*` flags,
+      install every subpath but the files matching the `#:exlude*` filters.
+      If both `#:include*` and `#:exclude*` are specified, the exclusion is done
+      on the inclusion list.
+
+Examples:
+
+- `(\"foo/bar\" \"share/my-app/\")`: Install bar to \"share/my-app/bar\".
+- `(\"foo/bar\" \"share/my-app/baz\")`: Install bar to \"share/my-app/baz\".
+- `(\"foo/\" \"share/my-app\")`: Install the content of foo inside \"share/my-app\",
+  e.g. install \"foo/sub/file\" to \"share/my-app/sub/file\".
+- `(\"foo/\" \"share/my-app\" #:include (\"sub/file\"))`: Install only \"foo/sub/file\" to
+\"share/my-app/sub/file\".
+- `(\"foo/sub\" \"share/my-app\" #:include (\"file\"))`: Install \"foo/sub/file\" to
+\"share/my-app/file\"."
+  (define (install-simple source target)
+    "Install SOURCE to TARGET.
+TARGET must point to a store location.
+SOURCE may be a file or a directory.
+If a directory, the directory itself is installed, not its content.
+if TARGET ends with a '/', the source is installed underneath."
+    (let ((target (if (string-suffix? "/" target)
+                      (string-append target (basename source))
+                      target)))
+      (mkdir-p (dirname target))
+      (copy-recursively source target)))
+
+  (define (install-file file target)
+    (let ((dest (string-append target
+                               (if (string-suffix? "/" target)
+                                   (string-append "/" file)
+                                   file))))
+      (format (current-output-port) "`~a' -> `~a'~%" file dest)
+      (mkdir-p (dirname dest))
+      (copy-file file dest)))
+
+  (define* (make-file-predicate suffixes matches-regexp #:optional (default-value #t))
+    "Return a predicate that returns #t if its file argument matches the
+SUFFIXES or the MATCHES-REGEXP.  If neither SUFFIXES nor MATCHES-REGEXP is
+given, then the predicate always returns DEFAULT-VALUE."
+    (if (or suffixes matches-regexp)
+        (let* ((suffixes (or suffixes '()))
+               (regexps (map make-regexp (or matches-regexp '())))
+               (predicates (append
+                            (map (lambda (str)
+                                   (cut string-suffix? str <>))
+                                 suffixes)
+                            (map (lambda (regexp)
+                                   (cut regexp-exec regexp <>))
+                                 regexps))))
+          (lambda (file)
+            (any (cut <> file) predicates)))
+        (const default-value)))
+
+  (define* (install-file-list source target #:key include exclude include-regexp exclude-regexp)
+    ;; We must use switch current directory to source so that `find-files'
+    ;; returns file paths relative to source.
+    (with-directory-excursion source
+      (let* ((exclusion-pred (negate (make-file-predicate exclude exclude-regexp #f)))
+             (inclusion-pred (make-file-predicate include include-regexp))
+             (file-list
+              (filter! exclusion-pred
+                       (find-files "." (lambda (file _stat)
+                                         (inclusion-pred file))))))
+        (map (cut install-file <> (if (string-suffix? "/" target)
+                                      target
+                                      (string-append target "/")))
+             file-list))))
+
+  (define* (install source target #:key include exclude include-regexp exclude-regexp)
+    (set! target (string-append (assoc-ref outputs "out") "/" target))
+    (let ((filters? (or include exclude include-regexp exclude-regexp)))
+      (when (and (not (file-is-directory? source))
+                 filters?)
+        (error "Cannot use filters when SOURCE is a file."))
+      (let ((multi-files-in-source?
+             (or (string-suffix? "/" source)
+                 (and (file-is-directory? source)
+                      filters?))))
+        (if multi-files-in-source?
+            (install-file-list source target
+                               #:include include
+                               #:exclude exclude
+                               #:include-regexp include-regexp
+                               #:exclude-regexp exclude-regexp)
+            (install-simple source target)))))
+
+  (for-each (lambda (plan) (apply install plan)) install-plan)
+  #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)
+    (delete 'configure)
+    (delete 'build)
+    (delete 'check)
+    (replace 'install install)))
+
+(define* (copy-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))
+
+;;; copy-build-system.scm ends here