snakemake-graph-save: Return the name of the output file

This will allow the graphing commands to save and display the graph
when the user is running an Emacs that was not built with ImageMagick
support.

When the user provides all-blank input or does not confirm an
overwrite, raise a user error so that the caller doesn't have to check
for a nil return value.

1 files changed, 14 insertions, 6 deletions

diff --git a/snakemake.el b/snakemake.el
index fb8d59d..830da96 100644
--- a/snakemake.el
+++ b/snakemake.el
@@ -530,23 +530,31 @@ $ snakemake -s <current file> --{dag,rulegraph} | display"
 
 (defun snakemake-graph-save ()
   "Save graph in current buffer to file.
+
 The graph will be processed by `snakemake-dot-program'.  The
 default extension of the output file is
 `snakemake-graph-default-extension', but you can enter any
-extension that the dot program supports."
+extension that the dot program supports.
+
+Return the name of the output file."
   (interactive)
   (unless snakemake-graph-id
     (user-error "Not in Snakemake graph buffer"))
   (let ((file (read-file-name "To file: " nil nil nil
                               (concat snakemake-graph-id
                                       snakemake-graph-default-extension))))
-    (unless (or (string-match-p "\\`\\s-*\\'" file)
-                (and (file-exists-p file)
-                     (not (y-or-n-p
-                           (concat file " already exists.  Overwrite?")))))
+    (cond
+     ((string-match-p "\\`\\s-*\\'" file)
+      (user-error "No output file specified"))
+     ((and (file-exists-p file)
+           (not (y-or-n-p
+                 (concat file " already exists.  Overwrite?"))))
+      (user-error "Aborted"))
+     (t
       (call-process-region (point-min) (point-max)
                            snakemake-dot-program nil (list :file file) nil
-                           "-T" (file-name-extension file)))))
+                           "-T" (file-name-extension file))
+      file))))
 
 (defvar snakemake-graph-mode-map
   (let ((map (make-sparse-keymap)))