Bug 8949 – [CTFE] ICE(ctfeexpr.c) copying a reference to a null AA

This code doesn't work: string test() { import std.csv; static struct Layout { string a, b; } static struct MapData { string[string] map; } MapData md; foreach (data; csvReader!Layout("a,")) { md.map[data.a] = data.b; } return md.map.get("b", null); } void main() { //import std.stdio; //writeln(test()); // <- OK pragma(msg, test()); // <- NG } Result: main.d(9): Error: Internal Compiler Error: CTFE literal Layout(['a'],null).b Assertion failure: '0' on line 353 in file 'ctfeexpr.c'

Reduced test case: struct S { int[int] a; } void baz(ref int[int] x) { auto m = x.dup; } int bar() { S s; baz(s.a); return 1; } static assert(bar()); --- Applies to any case where you pass an AA by reference _when it is null_, and then duplicate it. <sigh> This is the bizarre "magic null" semantics that happen only with AAs. It causes dozens of special cases.

The original case has worked from 2.063. The reduced test case in comment#1 works from 2.066 git-head, because AA implementation is changed to UFCS style.