Issue 3560: Completion_heads_engraver with \scaleDurations

input/regression/completion-heads-factor.ly

-\version "2.16.0"
+\version "2.17.28"
 
-\header{
+\header {
 texidoc="
-
-If the @code{Note_heads_engraver} is replaced by the @code{Completion_heads_engraver},
-notes with a duration factor still keep their requested appearance.
-
+If the @code{Note_heads_engraver} is replaced by the
+@code{Completion_heads_engraver}, notes with a duration factor will be
+split into notes with the same factor, allowing for consistent use of
+@code{\\scaleDurations} for matching meters.
 "
 }
 
-\layout { ragged-right= ##t }
+SplitThem =
+\with {
+  \remove "Note_heads_engraver"
+  \consists "Completion_heads_engraver"
+  \remove "Rest_engraver"
+  \consists "Completion_rest_engraver"
+}
 
+tup =
+#(define-music-function (parser location m) (ly:music?)
+#{
+  \tag old $m
+  \tag new \tuplet 3/2 $m
+#})
 
-\new Voice \with {
-    \remove "Note_heads_engraver"
-    \consists "Completion_heads_engraver"
-} \relative c'{
+untup =
+#(define-music-function (parser location m) (ly:music?)
+#{
+  \tag old \shiftDurations 0 1 $m
+  \tag new $m
+#})
 
-  c\breve |
-  c1*2 |
-  c2*4 |
-  c8*20
+melody =
+{
+  \tup { c'1 e' g' }
+  \tup { g'\breve a' g' }
+  \untup g'\longa
 }
+
+\score {
+  <<
+    \new MensuralStaff
+    {
+      \clef "alto"
+      \time 3/2
+      \keepWithTag old \melody
+      \bar "|."
+    }
+    \new Staff \with { timeSignatureFraction = 2/2
+                       \override BarLine.transparent = ##t }
+    {
+      \new Voice
+      {
+        \scaleDurations 3/1
+        \shiftDurations 1 0
+        \keepWithTag new \melody
+      }
+      \revert Staff.BarLine.transparent
+    }
+    \new Staff \with { timeSignatureFraction = 2/2 }
+    {
+      \new Voice \SplitThem
+      {
+        \scaleDurations 3/1
+        \shiftDurations 1 0
+        \keepWithTag new \melody
+      }
+    }
+  >>
+}