Let general-column deal reliable with empty args (issue 346030043 by address@hidden)

[thomasmorley65]

Reviewers: ,

Description:
Let general-column deal reliable with empty args

Previously an args-list of empty-stencils issued a programming error:
  Improbable offset for stencil: -inf staff space
This patch removes empty stencils from the args-list.
If args-list is empty, an empty stencil is returned.

Please review this at https://codereview.appspot.com/346030043/

Affected files (+16, -6 lines):
  M scm/define-markup-commands.scm


Index: scm/define-markup-commands.scm
diff --git a/scm/define-markup-commands.scm b/scm/define-markup-commands.scm
index  
0eb9ed93542ea9e7f61abaaf5a890fb8ff6ed0db..a1a8d86593fabd48a40a1909e1ed38b02ff70a5d  
100644
--- a/scm/define-markup-commands.scm
+++ b/scm/define-markup-commands.scm
@@ -1999,12 +1999,22 @@ setting of the @code{direction} layout property.
                (interpret-markup-list layout props args)))

 (define (general-column align-dir baseline mols)
-  "Stack @var{mols} vertically, aligned to  @var{align-dir} horizontally."
-
-  (let* ((aligned-mols (map (lambda (x) (ly:stencil-aligned-to x X  
align-dir)) mols))
-         (stacked-stencil (stack-lines -1 0.0 baseline aligned-mols))
-         (stacked-extent (ly:stencil-extent stacked-stencil X)))
-    (ly:stencil-translate-axis stacked-stencil (- (car stacked-extent)) X  
)))
+  "Stack @var{mols} vertically, aligned to @var{align-dir} horizontally.
+Remove empty stencils from @var{mols}.  If @var{mols} is an empty list  
return
address@hidden"
+  (let ((aligned-mols
+          (filter-map
+            (lambda (x)
+              (if (ly:stencil-empty? x)
+                  #f
+                  (ly:stencil-aligned-to x X align-dir)))
+            mols)))
+    (if (pair? aligned-mols)
+        (let* ((stacked-stencil (stack-lines -1 0.0 baseline aligned-mols))
+               (stacked-extent (ly:stencil-extent stacked-stencil X)))
+          (ly:stencil-translate-axis
+            stacked-stencil (- (car stacked-extent)) X))
+        empty-stencil)))

 (define-markup-command (center-column layout props args)
   (markup-list?)