build: asdf-build-system: Use SBCL source in CL packages.

* guix/build/asdf-build-system.scm (copy-files-to-output): Don't attempt to
  reset timestamps on files without write access.
  (install): When parent SBCL package is in the inputs, use its source.  This
  way we get possibly patched sources in CL packages as well (e.g. for FFI).
  This is also useful for sources that generate files on load-op, like cl-unicode.

* guix/build-system/asdf.scm (package-with-build-system): Forward the SBCL
  parent as a native input so that it can be used in the above install phase.

guix/build-system/asdf.scm

@@ -230,7 +230,10 @@ set up using CL source package conventions."
              ((#:phases phases) (list phases-transformer phases))))
           (inputs (new-inputs package-inputs))
           (propagated-inputs (new-propagated-inputs))
-          (native-inputs (new-inputs package-native-inputs))
+          (native-inputs (append (if target-is-source?
+                                     (list (list (package-name pkg) pkg))
+                                     '())
+                                 (new-inputs package-native-inputs)))
           (outputs (if target-is-source?
                        '("out")
                        (package-outputs pkg)))))

guix/build/asdf-build-system.scm

@@ -85,7 +85,8 @@ valid."
     ;; files before compiling.
     (for-each (lambda (file)
                 (let ((s (lstat file)))
-                  (unless (eq? (stat:type s) 'symlink)
+                  (unless (or (eq? (stat:type s) 'symlink)
+                              (not (access? file W_OK)))
                     (utime file 0 0 0 0))))
               (find-files source #:directories? #t))
     (copy-recursively source target #:keep-mtime? #t)
@@ -97,12 +98,53 @@ valid."
      (find-files target "\\.asd$"))
     #t))
 
-(define* (install #:key outputs #:allow-other-keys)
+(define* (install #:key inputs outputs #:allow-other-keys)
-  "Copy and symlink all the source files."
+  "Copy and symlink all the source files.
+The source files are taken from the corresponding compile package (e.g. SBCL)
+if it's present in the native-inputs."
   (define output (assoc-ref outputs "out"))
-  (copy-files-to-output output
+  (define package-name
     (package-name->name+version
-                         (strip-store-file-name output))))
+     (strip-store-file-name output)))
+  (define (no-prefix pkgname)
+    (if (string-index pkgname #\-)
+        (string-drop pkgname (1+ (string-index pkgname #\-)))
+        pkgname))
+  (define parent
+    (match (assoc package-name inputs
+                  (lambda (key alist-car)
+                    (let* ((alt-key (no-prefix key))
+                           (alist-car (no-prefix alist-car)))
+                      (or (string=? alist-car key)
+                          (string=? alist-car alt-key)))))
+      (#f #f)
+      (p (cdr p))))
+  (define parent-name
+    (and parent
+         (package-name->name+version (strip-store-file-name parent))))
+  (define parent-source
+    (and parent
+         (string-append parent "/share/common-lisp/"
+                        (string-take parent-name
+                                     (string-index parent-name #\-))
+                        "-source")))
+
+  (define (first-subdirectory directory) ; From gnu-build-system.
+    "Return the file name of the first sub-directory of DIRECTORY."
+    (match (scandir directory
+                    (lambda (file)
+                      (and (not (member file '("." "..")))
+                           (file-is-directory? (string-append directory "/"
+                                                              file)))))
+      ((first . _) first)))
+  (define source-directory
+    (if (and parent-source
+             (file-exists? parent-source))
+        (string-append parent-source "/" (first-subdirectory parent-source))
+        "."))
+
+  (with-directory-excursion source-directory
+    (copy-files-to-output output package-name)))
 
 (define* (copy-source #:key outputs asd-system-name #:allow-other-keys)
   "Copy the source to the library output."