Bug 21709 – std.conv.emplace not usable in betterC - 2.096

Our CI updated to dmd 2.096 and this error showed up: /root/dlang/dmd-2.096.0/linux/bin64/../../src/druntime/import/core/internal/lifetime.d(35,13): Error: Cannot use try-catch statements with -betterC /root/dlang/dmd-2.096.0/linux/bin64/../../src/druntime/import/core/internal/lifetime.d(57,21): Error: template instance `core.internal.lifetime.emplaceRef!(EntityManager, EntityManager, uint, uint, uint).emplaceRef.S.__ctor!()` error instantiating CI job url: https://gitlab.com/mmcomando/bubel-ecs/-/jobs/1095299347 From error message it seems that core.internal.lifetime.emplaceRef uses try-catch statement which is not supported by -betterC. I have tried to look for the code on github but I have not found lines with try-catch in druntime/import/core/internal/lifetime.d(35,13) so I am not sure if try-catch is the problem. Part of our code which uses emplace: static T* make(T, Args...)(Args args) { T* ret = cast(T*) malloc(T.sizeof); static import std.conv; static if (__traits(isPOD, T)) { __gshared immutable T init = T.init; memcpy(ret, &init, T.sizeof); } else static if (is(T == struct)) std.conv.emplace(ret, args); return ret; }

I was told that this code reproduces the issue: import std.conv : emplace; struct AA { ~this() { } } extern(C) void main() { AA aa; emplace(&aa, AA.init); }

This regression was introduced by enabling -preview=dtorfields by default[1]. This preview inserts a destructor call into constructors that is executed when they abort with an exception (using a generated try ... catch ...). DMD apparently fails to infer `nothrow` given that `-betterC` prohibits exceptions. [1] https://github.com/dlang/dmd/pull/11656

(In reply to moonlightsentinel from comment #2) > (using a generated try ... catch EDIT: Only for functions that aren't `nothrow`

dlang/dmd pull request #12277 "Fix 21709 - Don't generate try-catch in betterC code for dtorfields" was merged into stable: - afebdfa54ec01005da6ec62bc1249917b3b75a76 by MoonlightSentinel: Fix 21709 - Don't generate try-catch in betterC code for dtorfields The code may never throw exceptions in betterC mode, so it cannot abort the ctor with an uncaught exception. https://github.com/dlang/dmd/pull/12277

*** Issue 21720 has been marked as a duplicate of this issue. ***

Thanks for quick fix!

dlang/dmd pull request #12408 "Merge stable into master" was merged into master: - 6a36649a96f8f01e2e39a4224ff6bd58fc4e1667 by MoonlightSentinel: Fix 21709 - Don't generate try-catch in betterC code for dtorfields The code may never throw exceptions in betterC mode, so it cannot abort the ctor with an uncaught exception. https://github.com/dlang/dmd/pull/12408