cmake: De-duplicate libraries where possible #35756

hebasto commented at 3:47 PM on July 20, 2026: member

Set the CMP0156 and CMP0179 policies to NEW. CMP0156 de-duplicates libraries on link lines based on linker capabilities; CMP0179 makes this de-duplication keep the first occurrence of static libraries. This silences Apple linker "ignoring duplicate libraries" warnings.

Both policies are gated on CMP0179, which requires CMake >=3.31, to avoid the intermediate CMake 3.29/3.30 behaviour where only CMP0156 is available. This requirement is satisfied by the current Homebrew package and the Guix build environment. On older versions, the policy guard makes this a no-op.

The Guix scripts for macOS have been updated to turn linker warnings into errors, as is done for other targets.

hebasto added the label Build system on Jul 20, 2026

DrahtBot commented at 3:47 PM on July 20, 2026: contributor

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For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35756.

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fanquake commented at 3:53 PM on July 20, 2026: member

Would be good to clarify what has changed since you last PR'd this: #31504.

fanquake referenced this in commit 1714953eff on Jul 27, 2026

fanquake referenced this in commit 3f70305cf8 on Jul 27, 2026

fanquake referenced this in commit b12a70f330 on Jul 29, 2026

Kino1994 referenced this in commit 1c39296f20 on Aug 2, 2026

cmake: De-duplicate libraries where possible

Set the CMP0156 and CMP0179 policies to NEW. CMP0156 de-duplicates
libraries on link lines based on linker capabilities; CMP0179 makes
this de-duplication keep the first occurrence of static libraries.
This silences Apple linker "ignoring duplicate libraries" warnings.

Both policies are gated on CMP0179, which requires CMake >=3.31, to
avoid the intermediate CMake 3.29/3.30 behaviour where only CMP0156
is available. This requirement is satisfied by the current Homebrew
package and the Guix build environment. On older versions the policy
guard makes this a no-op.

1714370aa6

hebasto force-pushed on Aug 12, 2026

hebasto marked this as ready for review on Aug 12, 2026

hebasto commented at 11:19 AM on August 12, 2026: member

Would be good to clarify what has changed since you last PR'd this: #31504.

CMake's de-duplication behaviour has stabilised.
There is now a concrete motivation beyond log noise: extending the Guix warnings-as-errors treatment to Darwin (https://github.com/bitcoin/bitcoin/commit/b12a70f330d0ffcc3064ecf2643f8cfe765cf9c8) is blocked on the "ignoring duplicate libraries" warnings this PR silences.

From #31504 (comment):

Also not sure. Seems like this was introduced in 3.29, but then the behaviour was changed again 2 versions later in 3.31. Would we be opting into that as well? Then, depending on the version, we'd potentially have CMake behaving 3 different ways at link time.

Reworked to avoid the intermediate behaviour of CMake 3.29 or 3.30.

fanquake commented at 12:35 PM on August 12, 2026: member

motivation beyond log noise: extending the Guix warnings-as-errors treatment to Darwin

Why not do that here, if that is the motivation?

hebasto commented at 6:52 PM on August 12, 2026: member

My Guix build:

aarch64
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guix: Turn macOS linker warnings into errors e6c1483832

hebasto commented at 7:48 PM on August 12, 2026: member

motivation beyond log noise: extending the Guix warnings-as-errors treatment to Darwin

Why not do that here, if that is the motivation?

Thanks! Done.

My partial Guix build:

x86_64
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