Bug 20448 – Error: unknown when mutating an escaped member reference from a template function

The following complete program ``` import std.stdio : writeln; struct S { int x, y; } ref int member(string mem)(S p) { return p.x; } void main() { S p; //writeln(p.member!"x"); p.member!"x" = 2; writeln(p); } ``` fails to compile with this error: Error: unknown, please file report on issues.dlang.org With the mutation commented out, and the writeln uncommented, it fails more gracefully: ./x271.d(11): Error: returning p.x escapes a reference to parameter p, perhaps annotate with return ./x271.d(16): Error: template instance x271.member!"x" error instantiating Meanwhile a non-template version also has a proper error message: ``` import std.stdio : writeln; struct S { int x, y; } ref int member(S p) { return p.x; } void main() { S p; p.member = 2; writeln(p); } ``` ./x272.d(10): Error: returning p.x escapes a reference to parameter p, perhaps annotate with return

It looks like an UFCS problem. Using `member!"x"(p)` instead of `p.member!"x"` yields the correct error message.

@RazvanN7 created dlang/dmd pull request #10676 "Fix Issue 20448 - Error: unknown when mutating an escaped member reference from a template function" fixing this issue: - Fix Issue 20448 - Error: unknown when mutating an escaped member reference from a template function https://github.com/dlang/dmd/pull/10676

dlang/dmd pull request #10676 "Fix Issue 20448 - Error: unknown when mutating an escaped member reference from a template function" was merged into master: - 414460467bca449f5f28b44fe80ac8da5a0ea4ad by RazvanN7: Fix Issue 20448 - Error: unknown when mutating an escaped member reference from a template function https://github.com/dlang/dmd/pull/10676