Bug 7994 – Impure mixin generator of pure code inside pure functions too

This is yet another small refinement for the implementation of purity in D (I think this is more than an enhancement request, because I think the second example is supposed to work in a good purity implementation). This is wrong D2 code: import std.stdio; string foo() pure { return `writeln("hello");`; } void main() pure { mixin(foo()); } And the error message is correct because mixin(foo) causes main() call an impure function (DMD 2.060alpha): test.d(6): Error: pure function 'main' cannot call impure function 'writeln' But in this case: string foo() { import std.string; return xformat("%d", 1); } void main() pure { int x = mixin(foo()); } It gives: test.d(6): Error: pure function 'main' cannot call impure function 'foo' This time the error message is wrong, because desite foo() itself is not pure, mixin() calls it at compile-time, and the resulting main is equivalent to this, that is pure and correct: void main() pure { int x = 1; } So mixin() needs to be allowed to call impure functions too, even inside pure functions, as long as the resulting mixed-in code is pure. This is quite handy, because the generation of text to mix-in often calls functions like xformat and text that currently are not pure.

*** This issue has been marked as a duplicate of issue 6169 ***