fix #20617 Move constructors should not be POD

[WalterBright]

Blocked by #20616

[dlang-bot]

Thanks for your pull request, @WalterBright!

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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#20618"

[WalterBright]

I have no idea what this useless message means:

Executing: /home/runner/work/dmd/dmd/compiler/test/test_results/d_do_test-ut
1 modules passed unittests
Test directive `BAD` must be followed by a `:`
 ... runnable/test20855.d            -fPIC (-O)
 ... runnable/test18545.d            -fPIC (-inline -release -g -O)
 ... runnable/test28.d               -fPIC (-inline -release -g -O)
 ... runnable/test34.d               -fPIC (-inline -release -g -O)
 ... runnable/lazy.d                 -fPIC (-inline -release -g -O)
 ... runnable/test42.d               -fPIC (-inline -release -g -O)
 ... runnable/argufilem.d            -fPIC (-inline -release -g -O)
 ... runnable/xtest46.d             -preview=rvaluerefparam  -fPIC (-inline -release -g -O)
 ... runnable/xtest46_gc.d          -lowmem -Jrunnable -preview=rvaluerefparam  -fPIC (-inline -release -g -O)
 ... runnable/testgc3.d              -fPIC ()
 ... runnable/link14588.d            -fPIC (-allinst -unittest -debug -inline)
 ... runnable/link13415.d           -inline  -fPIC (-allinst -unittest -debug)
 ... runnable/paranoia.d             -fPIC ()
 ... runnable/template9.d           -preview=rvaluerefparam  -fPIC ()
 ... runnable/test23148.sh
 ... runnable/testassert_release.d   -fPIC (-checkaction=context)
 ... runnable/cov2.d                -cov  -fPIC ()
 ... runnable/test23083.d            -fPIC (-inline -release -g -O)
 ... runnable/test1[70](https://github.com/dlang/dmd/actions/runs/12540628566/job/34968140892?pr=20618#step:12:71)72.d           -inline  -fPIC (-release -O)
 ... runnable/test809.d              -fPIC (-inline -release -g -O)
 ... runnable/issue24401.d           -fPIC ()
 ... runnable/test3449.d             -fPIC (-inline -release -g -O)
 ... runnable/test19086.d           -g -L-export-dynamic  -fPIC ()
 ... runnable/test22376.c            -fPIC (-inline -release -g -O)
 ... runnable/sroa13220.d           -O -inline -boundscheck=off  -fPIC (-release -g)
 ... runnable/test21822.d            -fPIC (-inline -release -g -O)
 ... runnable/link14198a.sh
Failed to compile the `unit` test executable! (exit code -11)

[WalterBright]

What is the unit test executable? And why is there no message about what the error is?

[thewilsonator]

I think that refers to https://github.com/dlang/dmd/tree/master/compiler/test/unit those tests

[WalterBright]

Sadly, run.d neglects to mention where it is getting the dmd compiler to run from, etc., and how that can be redirected. The error message comes from the file unit_test_runner.d, which suffers from a near total lack of documentation. It has a main(), but has no instructions on how to build it, or even what files are needed.

We should go back to makefiles.

[thewilsonator]

Looking into it more closely https://github.com/dlang/dmd/blob/master/compiler/test/run.d#L132 is the command that is run when "unit test" is printed.

[thewilsonator]

#20620

[WalterBright]

I have sadly come to the conclusion that proper move constructors will break existing code. It seems to happen too much. This means that proper move construction can only happen when there are also copy constructors, as having both a move and a copy constructor has been previously disallowed. This is not too great a burden, as having a move constructor without a copy constructor doesn't seem to make much sense.