selector interpolation and nesting

[bassjobsen]

I'm not sure why the compiled CSS of the following snippets differs, could someone explain that?

@var1: ~"a,b";
@{var1}{c{p:1;}}

@var2: ~"a";
@var3: ~"b";
@{var2},@{var3}{c{p:1;}} 

Compiled CSS:

a,b c {
  p: 1;
}
a c,
b c {
  p: 1;
}

[seven-phases-max]

Currently selector interpolation ignores any comma or & in an interpolated variable (thus such variable is always interpreted as a single selector element). Eventually this is considered as something to be improved (see #1421, #1694, #1967 etc.).
A subtle remark though: ~"" is not necessary in this example (and ideally also to be avoided whenever possible in those "future" improvements since the purpose of ~"" (at least I prefer it to be so and thus hardly pushing this idea) is somewhat opposite).

[seven-phases-max]

Closing as a duplicate of #1421.