Address Eigen warnings - Update itkeigen library

[blowekamp]

There are warning on cdash like the following:

Modules/ThirdParty/Eigen3/src/itkeigen/../itkeigen/Eigen/src/Core/GenericPacketMath.h:655:61: warning: declaration shadows a local variable [-Wshadow-uncaptured-local]
return pminmax_impl<NaNPropagation, IsInteger>::run(a, b, EIGEN_BINARY_OP_NAN_PROPAGATION(Packet, (pmin)));

https://open.cdash.org/viewBuildError.php?type=1&buildid=10616735

Proposed PR #5482, suppressed these warnings, but @seanm commented that the fix is already in the library upstream.

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[seanm]

@phcerdan you seem adept at the git magic to update eigen, think you could do it again? :)

[phcerdan]

@seanm I am glad to do it, but I think is even better if we do it together. What do you think about a pair-programming session, so you get a grasp on how to do it yourself? :)

[pzaffino]

Hi,
is there any chance to use Eigen5?

Thanks,
Paolo

[blowekamp]

@seanm @phcerdan I seen a fix for the warning was made upstream:

Fetched https://gitlab.com/libeigen/eigen/-/commits/master/Eigen/src/Core/GenericPacketMath.h?search=EIGEN_BINARY_OP_NAN_PROPAGATION

Fetched https://gitlab.com/libeigen/eigen/-/commits/master/Eigen/src/Core/GenericPacketMath.h

Fetched https://gitlab.com/libeigen/eigen/-/commit/430e35fbd15d3c946d2d2ba19ec41c16ba217cb3

The specific upstream commit that fixed the -Wshadow warning is:

Commit: 430e35fbd15d3c946d2d2ba19ec41c16ba217cb3
Author: Sean McBride
Date: July 11, 2025
Title: "Fixed -Wshadow warning by renaming variables"
Merge Request: !1936

The fix changed line 641 in GenericPacketMath.h:

-#define EIGEN_BINARY_OP_NAN_PROPAGATION(Type, Func) [](const Type& a, const Type& b) { return Func(a, b); }
+#define EIGEN_BINARY_OP_NAN_PROPAGATION(Type, Func) [](const Type& aa, const Type& bb) { return Func(aa, bb); }

This change eliminated the shadow warning by renaming the lambda parameters from a/b to aa/bb, preventing them from shadowing the outer function parameters when the macro is expanded within functions that also use parameter names a and b.

But has not been back ported to our fork or ITK repos. These warnings are obfuscating other warnings on the dashboard and would be good to address.

[seanm]

When I see warnings on my bots, I try as best as I can to fix them upstream. But the git magic to integrate 3rd party stuff into ITK is not something I know...

[dzenanz]

Eigen's case is extra complicated.

[seanm]

And my git-fu is extra weak :)

[blowekamp]

Is there any history or documentation on ITK's forked repo?
https://github.com/InsightSoftwareConsortium/eigen

[dzenanz]

@phcerdan is the best person to answer. I remember he original had ITK's Eigen fork in some GitLab instance (I can't find which one right now), and it was only recently added to ISC GitHub org.

[phcerdan]

Hi, the original eigen fork is in: https://gitlab.kitware.com/phcerdan/eigen/-/tree/for/itk-master?ref_type=heads, but is cloned into https://github.com/InsightSoftwareConsortium/eigen as is.

The original approach is very similar to what VTK was doing with their third party eigen. The main difference is that we wanted to allow modules that depend on other libraries that use eigen to not have to change their upstreams and be able to use eigen with the original headers (no need to use itkeigen/core.h or similar custom path. An example of this is the ITKTotalVariation that uses proxTV (which depends on regular eigen).

In a nutshell, we branch at some point from upstream, we decided to follow master given the lack of releases of Eigen (5.0 came after more than 2 years without releases), and then rebase on top our custom CMake code, which is basically, first ignore the upstream CMake, select the parts we want, and install those. Eigen is easier in that sense because it's a header only for us.

I can guide you @blowekamp on how to do it, and we can properly document it, etc. I am lacking the time needed to be the only one with experience doing this with Eigen, I apologize.