5396 – [CTFE] Invalid code with nested functions in CTFE

The following code:
----
void outer(bool b)
{
 string inner()
 {
 if (b)
 {
 return "true";
 }
 else
 {
 return "false";
 }
 }
 pragma(msg, inner());
}
----
Compiles and evaluates without error, despite the dependence on the runtime value b.

Extended test cases (applies to delegate literals as well as inner functions):
void bug5396(int b)
{
 int inner() { return b; }
 static int staticInner() { return 6; }
 static assert(is(typeof(compiles!(
 function int () { return 7; }()
 ))));
 static assert(!is(typeof(compiles!(
 delegate int () { return b; }()
 ))));
 static assert(!is(typeof(compiles!(
 inner()
 ))));
 static assert(is(typeof(compiles!(
 staticInner()
 ))));
}
Patch in interpret.c, CallExp::interpret(). Problem is, this breaks bug 1461 which seems to be an important use case.
 if (!istate && fd && fd->isNested() && !fd->isStatic() &&
 /* BUG: Delegate literals report 'isNested()' even if they are
 * declared at module scope.
 */
 !(fd->isFuncLiteralDeclaration() && !fd->toParent2()->isFuncDeclaration()))
 {
 error("cannot directly interpret non-static nested function %s", fd->toChars());
 return EXP_CANT_INTERPRET;
 }
 if (pthis && fd)
 { // Member function call

https://github.com/D-Programming-Language/dmd/commit/04460186c70caa885935433138879d8684b1d14a