pgffor: new expand list option

doc/generic/pgf/text-en/pgfmanual-en-pgffor.tex

@@ -372,6 +372,27 @@ \section{Repeating Things: The Foreach Statement}
 \end{codeexample}
         %
     \end{key}
+
+    \begin{key}{/pgf/foreach/expand list=\marg{boolean} (default false)}
+        If this key is set to true the contents of the list are fully expanded
+        with |\edef| before further processing.  This allows using complex
+        macros which generate a list upon expansion without having to use an
+        intermediate macro.
+        %
+\begin{codeexample}[]
+\def\Iota#1#2{%
+  \ifnum\numexpr#1\relax<\numexpr#2\relax
+    \the\numexpr#1\relax,%
+    \expandafter\Iota\expandafter{\the\numexpr(#1)+1\relax}{#2}%
+  \else
+    \the\numexpr#2\relax
+  \fi}
+\foreach [expand list=true] \x in {\Iota{1}{5}} {
+  \x
+}
+\end{codeexample}
+      %
+    \end{key}
 \end{command}
 
 \begin{command}{\breakforeach}

tex/generic/pgf/utilities/pgffor.code.tex

@@ -79,10 +79,13 @@
     \fi%
 }
 
+\def\pgffor@expand@list@true{\let\pgffor@expand@list\edef}
+\def\pgffor@expand@list@false{\let\pgffor@expand@list\def}
 \def\pgffor@macro@list#1{%
   \expandafter\pgffor@normal@list\expandafter{#1}}
 \def\pgffor@normal@list#1{%
-  \def\pgffor@values{#1, \pgffor@stop,}%
+  \pgffor@expand@list\pgffor@values{#1}%
+  \expandafter\def\expandafter\pgffor@values\expandafter{\pgffor@values, \pgffor@stop,}%
   \ifx\pgffor@values\pgffor@emptyvalues
     \def\pgffor@values{\pgffor@stop,}%
   \fi%
@@ -619,6 +622,9 @@
     count/.code=\pgffor@count@parse#1\pgffor@stop,
     parse/.is if=pgffor@assign@parse,
     parse/.default=false,
+    expand list/.is if=pgffor@expand@list@,
+    expand list/.default=true,
+    expand list=false,
 }
 
 \def\pgffor@assign@parse#1{%