Bug 21244 – Error: expression `hasToString!(..., char)` of type `void` does not have a boolean value

Looks like a DMD problem with recursive templated types. Partial reduction: //////////////////////// test.d //////////////////////// import std.format; import std.stdio; struct M(_) { struct N { M* next; void print() { next.print(); } void toString(void delegate(const(char)[]) sink) { if (next) sink.formattedWrite("%s", *next); } } N* root; void print() { writeln(this); } void toString(void delegate(const(char)[]) sink) { if (root) sink.formattedWrite("%s", *root); } } M!int x; //////////////////////////////////////////////////////// Yields a wall of errors starting with: .../std/format.d(4420): Error: expression hasToString!(M!int, char) of type void does not have a boolean value

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