Bug 11503 – Type system breaking caused by implicit conversion for the value returned from pure function

From: http://forum.dlang.org/post/[email protected] If an immutable value is returned by pure function, compiler _must_ not implicitly convert it to mutable. Test case: import std.stdio; struct S { immutable(S)* s; this(int) immutable pure { s = &this; } int data; } immutable(S)* makes() pure { return new immutable S(0); } void main() { S* s = makes(); // s is mutable and contains an immutable reference to itself pragma(msg, typeof(s)); // mutable pragma(msg, typeof(s.s)); // immutable writefln("%s", s); // same address writefln("%s", s.s); // same address //s.s.data = 7; // this is immutable s.data = 3; // but this is not!!! }

Simpler example: import std.stdio; immutable int[] x = [1, 2, 3]; auto makes() pure { return x; } void main() { auto a = x; int[] b = makes(); writefln("%s %s", a.ptr, b.ptr); }

Placed a $150 bounty.

Seems to be a fairly simple issue. Regression-testing a fix right now.

Commit pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/80619240a71ea68c7d4733f5010263b8a04a46de Issue 11503 - immutable return value from pure function implicitly converts to mutable.