Bug#1029010: llvm-toolchain-15: autopkgtest regression

[Faidon Liambotis]

On Fri, Mar 03, 2023 at 05:46:15PM +0000, Simon McVittie wrote:
> I've cut down what I think is the root cause of this compile failure to
> a more minimal bug report: see #1032317.

That's super helpful, thanks :) Spoiler alert: I have a suspicion on the
root cause, I'll follow up there.

> I don't think this is *really* a regression, because in the version in
> bookworm, the autopkgtest didn't exercise compilation of C++ into
> WebAssembly at all.

This statement strictly speaking is true, but applies only if you look
at LLVM 15 in isolation. It *is* a regression, in the sense that this
works with llvm-toolchain-14, where the WebAssembly work was first
pushed, today, in both bookworm and sid. For example, retracing your
steps in #1032317 with s/15/14/ does not result into a failure.

> If I understand correctly, when compared with bookworm, the version in
> sid adds a new feature (the necessary -dev packages for compiling C++ into
> WebAssembly) and also adds a smoke-test for that feature, but the feature
> doesn't yet work as intended. Is that accurate?

Kind of -- again, strictly speaking, true for libc++-15-dev-wasm32.
However, there is a metapackage, libc++-dev-wasm32, which Depends on the
default implementation, which is libc++-14-dev-wasm32 right now. That
metapackage has at least one notable reverse B-D, firefox, using it to
build certain security/sandboxing features (RLBox[1], AIUI). That is to
say, this feature works (w/ 14) and does very useful things today. it
(seemingly) broke when it was ported to llvm-toolchain-15, which
src:firefox does not depend on directly.

1: https://rlbox.dev/

Regards,
Faidon