The following compiled with '-betterC': ===================================== @nogc nothrow: struct S { @nogc nothrow: this(this) { impl++; } ~this() { } int* impl; } struct C { S s1; S s2; } extern(C) int main() { return 0; } ===================================== Produces a meaningless error (no line number no file name): `Error: Cannot use try-catch statements with -betterC` Commenting either the postblit ctor or dtor makes the error go away. Expected: To get no error.
Errors out on dmd 2.0.78.3 and dmd 2.0.79-beta1 https://run.dlang.io/is/R6BWSz
Even more reduced test case: --- struct S { this(this) { } ~this() { } } struct C { S s1; S s2; } ---
Declaring `C` as --- struct C { S s1; } --- makes the test case compile.
A PR has been submitted to remove generation of the try-catch if the postblit is `nothrow`: https://github.com/dlang/dmd/pull/8184 I don't consider this a complete fix to this issue, but if it is accepted, it will allow one to attribute their postblit with `nothrow` to avoid the error in -betterC. I'm pondering a more thorough solution for -betterC, and intend to tackle that as another PR.
Ideally -betterC should imply `nothrow`, and any lowered code should work with this assumption. What is important to keep in mind is that if you require `this(this)` to be annotated with `nothrow` in order to compile - you need to fix the error message for the case where it isn't and using -betterC, the current error message is very bad.
I though more about this and I think betterC should imply nothrow *only for* compiler generated code. Making betterC nothrow by default will change semantics and basically split the language in two, as betterC code will have 2 different defaults depending on the switch. This means that betterC should start error out on non nothrow code, with a deprecation period for interim.
Commit pushed to master at https://github.com/dlang/dmd https://github.com/dlang/dmd/commit/8a33fb6c692d0b2c1f03ceeb65c28beaebd932a0 Add test for issue 18493
Commits pushed to master at https://github.com/dlang/druntime https://github.com/dlang/druntime/commit/d676ffa836204dded541101b74dff8ae8131ad5d Fix Issue 18493 - [betterC] Can't use aggregated type with postblit https://github.com/dlang/druntime/commit/a2cabb8e668434521aff45f4d064fcf48780fb11 Merge pull request #2184 from JinShil/betterC_nothrow Fix Issue 18493 - [betterC] Can't use aggregated type with postblit merged-on-behalf-of: Sebastian Wilzbach <sebi.wilzbach@gmail.com>
This is not yet fixed. Still needs https://github.com/dlang/dmd/pull/8253 and maybe some more druntime work.
@RazvanN7 created dlang/dmd pull request #15076 "Fix Issue 18493 - [betterC] Can't use aggregated type with postblit" fixing this issue: - Fix Issue 18493 - [betterC] Can't use aggregated type with postblit https://github.com/dlang/dmd/pull/15076
dlang/dmd pull request #15076 "Fix Issue 18493 - [betterC] Can't use aggregated type with postblit" was merged into master: - 490c8a26f6563e86b9df3cd4180afc2e6c8bb08c by RazvanN7: Fix Issue 18493 - [betterC] Can't use aggregated type with postblit https://github.com/dlang/dmd/pull/15076