fix bugzilla Issue 24836 - struct return by hidden struct arg does no…

[WalterBright]

…t need copy to become an rvalue

[dlang-bot]

Thanks for your pull request, @WalterBright!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	24836	normal	struct return by hidden struct arg does not need copy to become an rvalue

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#17033"

[WalterBright]

Oh why oh why are the phobos unittests run before the test suite? The build process builds the compiler, then tries to compile d_do_test, which relies on:

import std.algorithm;
import std.array;
import std.conv;
import std.datetime.stopwatch;
import std.datetime.systime;
import std.exception;
import std.file;
import std.format;
import std.meta : AliasSeq;
import std.process;
import std.random;
import std.range : chain;
import std.regex;
import std.path;
import std.stdio;
import std.string;
import core.sys.posix.sys.wait;

which tries to run the unittests while building it, and so everything must work perfectly in phobos and d_do_test for it to even get to the test suite. The comments in it say it is supposed to be called by the Makefile - what Makefile?

[WalterBright]

Why is it missing the simplest:

1. how to build it
2. how to run it

?

[WalterBright]

I found another way to debug it. d_do_test still needs much in the way of documentation.

[WalterBright]

Testing optimizations is rarely very practical.