Fix Bitcoin Core build errors from libmultiprocess headers #370

pull ryanofsky wants to merge 4 commits into bitcoin-core:master from ryanofsky:pr/sockinline changing 7 files +7 −7

ryanofsky commented at 12:11 AM on October 2, 2026: collaborator

Problem: Bumping the libmultiprocess subtree in Bitcoin Core to current master breaks the build with -Werror. GCC reports SocketError as an unused const variable in every file that includes mp/util.h without using it (-Wunused-const-variable, enabled by bitcoin/bitcoin#36275; CI failure), and the #if KJ_NO_EXCEPTIONS check added in #364 fails -Wundef when the macro is not defined.

Solution: Make SocketError an inline constexpr variable, the same change Bitcoin Core made to its own SocketError in bitcoin/bitcoin#35852, and check defined(KJ_NO_EXCEPTIONS) before testing its value. Also enable both warnings in CI here (-Wunused-const-variable in the GCC configs, -Wundef in default and llvm) so these problems are caught before a subtree update. Details are in the commit messages.

util: Make SocketError inline constexpr

Declare SocketError as an inline variable so the header does not define a
separate internal-linkage copy in every translation unit that includes it.
Bitcoin Core's build now enables -Wunused-const-variable (bitcoin/bitcoin#36275),
which with GCC warns about unused const variables defined in headers and
fails the build with -Werror in every file that includes mp/util.h without
using SocketError. Bitcoin Core made the same change to its own SocketError
definition in bitcoin/bitcoin#35852.

This change was written with Claude Opus 5.5 (1M context).

701449c165

ci: Enable -Wunused-const-variable in GCC jobs

Bitcoin Core builds the libmultiprocess subtree with -Wunused-const-variable
(bitcoin/bitcoin#36275). With GCC this warns about unused const variables
defined in headers, so a header-level constexpr that is not inline breaks the
Bitcoin Core build. Enable it in the GCC-based CI configs to catch this here
first. Clang's -Wunused-const-variable does not warn about variables defined
in headers, so it is not added to the clang configs.

This change was written with Claude Opus 5.5 (1M context).

a8c64c7faa

proxy-types: Avoid -Wundef error when KJ_NO_EXCEPTIONS is not defined

Check that KJ_NO_EXCEPTIONS is defined before testing its value. Bitcoin
Core builds the libmultiprocess subtree with -Wundef, so the plain
`#if KJ_NO_EXCEPTIONS` check added in #364 fails the build with -Werror
whenever the macro is not defined, which is the normal case.

This change was written with Claude Opus 5.5 (1M context).

debd42955e

ci: Enable -Wundef in default and llvm jobs

Bitcoin Core builds the libmultiprocess subtree with -Wundef, so a
preprocessor check on an undefined macro breaks the Bitcoin Core build.
Enable it in one GCC and one clang config to catch this here first.

This change was written with Claude Opus 5.5 (1M context).

3577d23f61

DrahtBot commented at 12:11 AM on October 2, 2026: none


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ACK maflcko, ViniciusCestarii, hebasto, Sjors

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Conflicts

Reviewers, this pull request conflicts with the following ones:
- #342 (Allow request cancellation for wrapped C++ methods by xyzconstant)
- #231 (Add windows support by ryanofsky)
If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.
maflcko commented at 4:02 PM on October 2, 2026: contributor

lgtm ACK 3577d23f616ec6e8d601d14452a5793f9d386708
ViniciusCestarii commented at 4:56 PM on October 2, 2026: contributor

tACK 3577d23f616ec6e8d601d14452a5793f9d386708

Confirmed Bitcoin Core builds with libmultiprocess with these changes
hebasto approved
hebasto commented at 5:58 PM on October 3, 2026: member

ACK 3577d23f616ec6e8d601d14452a5793f9d386708, I have reviewed the code and it looks OK.
Sjors commented at 2:16 PM on October 7, 2026: member

ACK 3577d23f616ec6e8d601d14452a5793f9d386708
Sjors referenced this in commit 24b093a804 on Oct 7, 2026

Type	Reviewers
ACK	maflcko, ViniciusCestarii, hebasto, Sjors

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#364 util: Error out at compile time if KJ_NO_EXCEPTIONS is set

Fix Bitcoin Core build errors from libmultiprocess headers #370

Reviews

Conflicts