Simplify the functions dealing with source/dest file paths (see #97)

This commit introduces pb/expand-file-specs, which expands a :files
list into a list of (SOURCE . DEST) pairs -- SOURCE is the relative
path of a source file or directory, and DEST is the relative path to
which it should be copied. By mapcar'ing this list, it's then easy to
get lists of the source and destination files, and copying files
becomes as easy as copying each SOURCE to its corresponding DEST.

package-build.el

@@ -466,54 +466,43 @@ of the same-named package which is to be kept."
           (directory-files package-build-recipes-dir t "^[^.]")))
 
 
-(defun pb/source-file-list (files)
-  "Generate a flat source file listing from FILES."
-  (mapcan (lambda (entry)
-            (if (consp entry)
-                (pb/source-file-list (cdr entry))
-              (list entry)))
-          files))
-
-(defun pb/target-file-list (files)
-  "Generate a flat target file listing from FILES."
-  (mapcan (lambda (entry)
-            (if (consp entry)
-                (loop for res in (pb/target-file-list (cdr entry))
-                      collect (concat (car entry) "/" res))
-              (list (file-name-nondirectory entry))))
-          files))
+(defun pb/expand-file-specs (dir specs &optional subdir)
+  "In DIR, expand SPECS, optionally under SUBDIR.
+The result is a list of (SOURCE . DEST), where SOURCE is a source
+file path and DEST is the relative path to which it should be copied."
+  (let ((default-directory dir)
+        (prefix (if subdir
+                    (format "%s/" subdir)
+                  "")))
+    (mapcan
+     (lambda (entry)
+       (if (consp entry)
+           (pb/expand-file-specs dir
+                                 (cdr entry)
+                                 (concat prefix (car entry)))
+         (mapcar (lambda (f)
+                   (cons f (concat prefix (file-name-nondirectory f))))
+                 (or (file-expand-wildcards entry)
+                     (error "No matching file(s) found in %s: %s"
+                            dir
+                            entry)))))
+     specs)))
 
 (defun pb/expand-config-file-list (dir config)
-  "In DIR, expand the :files for CONFIG and flatten the list."
-  (pb/expand-file-list dir (or (plist-get config :files) (list "*.el"))))
-
-(defun pb/expand-file-list (dir files)
-  "In DIR, expand FILES, some of which may be shell-style wildcards."
-  (mapcan (lambda (entry)
-            (if (consp entry)
-                (list (cons (car entry) (pb/expand-file-list dir (cdr entry))))
-              (let ((default-directory dir))
-                (file-expand-wildcards entry))))
-          files))
+  "In DIR, expand the :files for CONFIG using 'pb/expand-file-specs."
+  (pb/expand-file-specs dir (or (plist-get config :files) (list "*.el"))))
 
 (defun pb/expand-source-file-list (dir config)
-  "Shorthand way to expand paths in DIR for files listed in CONFIG."
-  (pb/source-file-list (pb/expand-config-file-list dir config)))
+  "Shorthand way to expand paths in DIR for source files listed in CONFIG."
+  (mapcar 'car (pb/expand-config-file-list dir config)))
 
-(defun pb/copy-package-files (files source target)
-  "Copy FILES from the SOURCE directory to TARGET directory.
-FILES is in the form (FILE-OR-CONS ...).
-
-FILE-OR-CONS is either a path relative to SOURCE or
-a cons of the form (TARGET-SUBDIR FILE-OR-CONS).
-
-TARGET-SUBDIR is a directory relative to TARGET."
-  (loop for fn in files
-        if (consp fn) do (pb/copy-package-files (cdr fn)
-                          source (expand-file-name (car fn) target))
-        else do (pb/copy-file
-                 (expand-file-name fn source)
-                 (expand-file-name (file-name-nondirectory fn) target))))
+(defun pb/copy-package-files (files source-dir target-dir)
+  "Copy FILES from SOURCE-DIR to TARGET-DIR.
+FILES is a list of (SOURCE . DEST) relative filepath pairs."
+  (loop for (source-file . dest-file) in files
+        do (pb/copy-file
+            (expand-file-name source-file source-dir)
+            (expand-file-name dest-file target-dir))))
 
 (defun pb/copy-file (file newname)
   "Copy FILE to NEWNAME and create parent directories for NEWNAME if they don't exist."
@@ -549,7 +538,7 @@ TARGET-SUBDIR is a directory relative to TARGET."
        ((not version)
         (message "Unable to check out repository for %s" name))
        ((= 1 (length files))
-        (let* ((pkg-source (expand-file-name (car files) pkg-cwd))
+        (let* ((pkg-source (expand-file-name (caar files) pkg-cwd))
                (pkg-target (expand-file-name
                             (concat file-name "-" version ".el")
                             package-build-archive-dir))
@@ -563,8 +552,8 @@ TARGET-SUBDIR is a directory relative to TARGET."
           (copy-file pkg-source pkg-target)
           (pb/add-to-archive-contents pkg-info 'single)))
        ((< 1 (length  files))
-        (let* ((pkg-files (pb/target-file-list files))
-               (pkg-dir (concat file-name "-" version))
+        (let* ((pkg-dir (concat file-name "-" version))
+               ;; TODO: What if the upstream "-pkg.el" file is in a subdir?
                (pkg-file (concat file-name "-pkg.el"))
                (pkg-info
                 (pb/merge-package-info
@@ -589,13 +578,11 @@ TARGET-SUBDIR is a directory relative to TARGET."
                                                  package-build-working-dir)))
                              pkg-info)
 
-          (add-to-list 'pkg-files pkg-file)
-
           (pb/create-tar
            (expand-file-name
             (concat file-name "-" version ".tar") package-build-archive-dir)
            pkg-dir
-           pkg-files)
+           (append (mapcar 'cdr files) (list pkg-file)))
 
           (delete-directory pkg-dir t nil)
           (pb/add-to-archive-contents pkg-info 'tar)))