Bug 19213 – goto skips declaration of variable in std.algorithm.iteration.joiner

The upgrade of libphobos 2.081.2-1 -> 2.082.0-1 on Arch Linux introduced this error. I do not have the time to investigate the error in detail but wanted to report it anyway. Here is the full error message: /usr/include/dlang/dmd/std/algorithm/iteration.d-mixin-2675(2677,31): Error: goto skips declaration of variable std.algorithm.iteration.joiner!(FilterResult!(isAmgiguouslyAlignedRead, ChunkByImpl!(haveEqualIds, FilterResult!(unaryFun, AlignmentChain[])))).joiner.Result.this.__tmpfordtor3418 at /usr/include/dlang/dmd/std/algorithm/iteration.d-mixin-2675(2687,28)

So, you have a piece of code that compiled with 2.081.2 that now fails with 2.082.0, and this is the error message? We need a code example that reproduces the problem, or we can't really do anything.

If you can't easily provide a simplified example, when you have time, you can use dustmite to try to reduce your code to provide one: https://github.com/CyberShadow/DustMite/wiki

I ran into this myself when attempting compile a service that we've had in production for more than a year after updating to DMD 2.083.0. I was able to create a small artificial repro case, runnable here: https://run.dlang.io/is/ssx7CP import std.algorithm; import std.range; void main() { static struct Rec { int foo; } auto results = [[1,2], [3,4]] .map!(q => q.map!Rec.chunkBy!"a.foo") .joiner; } This is definitely a regression as this code builds with DMD 2.080.1 and prior.

I reduced the example a bit more. The struct is not involved in the error. import std.algorithm; import std.range; void main() { auto results = [[1,2], [3,4]] .map!(q => q.chunkBy!"a") .joiner; }

While I'm not convinced the `goto`s in the `pop{Front,Back}EmptyElements` mixins in Phobos are the most elegant way of expressing the logic, the issue is that the frontend warns about a skipped *temporary* variable declaration, whose lifetime doesn't extend to the goto target. It may be enough to exclude `STC.temp` vars from the error, just like for `STC.exptemp` in https://github.com/dlang/dmd/blob/06d579823bddf8cae735408f6cc81d4789ace520/src/dmd/statement.d#L2270. I think the temporaries are bound to their statement (which cannot cross the goto label) but I'm not 100% sure that's always the case.

(In reply to kinke from comment #5) > While I'm not convinced the `goto`s in the `pop{Front,Back}EmptyElements` > mixins in Phobos are the most elegant way of expressing the logic, the issue > is that the frontend warns about a skipped *temporary* variable declaration, > whose lifetime doesn't extend to the goto target. > This is true: the issue spawns from the frontend. Until this get's fixed, I have a PR to fix this https://github.com/dlang/phobos/pull/6803

Commits pushed to master at https://github.com/dlang/phobos https://github.com/dlang/phobos/commit/6572e4abb338127e2fd12cd562133e8f71a35311 Fix Issue 19213 - goto skips declaration of variable in std.algorithm.iteration.joiner https://github.com/dlang/phobos/commit/07ea0e020113320f01a2028d40e5d494934dc9b0 Merge pull request #6803 from edi33416/issue_19213 Fix Issue 19213 - goto skips declaration of variable in std.algorithm…