BUG: Do not compile NrrdIO's sampleIO.c demo into the library

[hjmjohnson]

sampleIO.c is NrrdIO's usage demo and defines main(). Compiling it into libITKNrrdIO makes the library export main(), so downstream executables that link ITK's NrrdIO alongside gtest_main can silently resolve to the demo instead of their own entry point — on ITK 6.0.0 this silently deleted 17 BRAINSTools unit tests from a passing suite (413 → 396). One-line removal; ITK builds no executable from this file.

This is the minimal unblock for ITKv6 downstreams. The durable fix is upstream in NrrdIO (nrrdio_SRCS derived from NrrdIO_Srcs.txt rather than kept as a second hand-written copy), which a future re-vendor picks up.

Symptom — a GTest binary that was silently NrrdIO's demoIO

The executables build and run. They are simply the wrong program:

$ ImageCalculatorUtilsGTest --gtest_list_tests      # ITK 6.0.0, before
(from Teem 2.0.0, early 2026)
demoIO: trouble reading "--gtest_list_tests":
[nrrd] nrrdLoad: fopen("--gtest_list_tests","rb") failed

gtest_discover_tests runs the binary at build time to enumerate tests, receives Teem's banner instead of a test list, parses zero, and registers nothing. ctest then reports 396 tests passed — success, with 17 tests absent rather than failing. Nothing errors or warns at any layer.

$ nm -g libITKNrrdIO-6.0.a | grep ' T _main'
sampleIO.c.o: T _main            # ITK 6.0.0  -- a library defining main()
                                 # ITK 5.4.6  -- no match

ITK 5.4.6 is unaffected because its vendored list predates the change.

Why sampleIO.c is not library code

Three artifacts already vendored beside CMakeLists.txt say so:

file	says
0-README.txt:93	"Tiny little command-line program demonstrating the basic NrrdIO API."
sample-GNUmakefile:56,74	ALL = libNrrdIO.a sampleIO — two separate products; sampleIO : sampleIO.c ... -L. -lNrrdIO links against the library
NrrdIO_Srcs.txt	41 Teem-extracted sources; omits sampleIO.c

Only nrrdio_SRCS in CMakeLists.txt listed it — and that is the list the build executes. git grep sampleIO confirms ITK has no add_executable for it; it built as nothing but an archive member.

It entered ITK via 9f0a5d3 (ENH: Update NrrdIO from upstream), inherited from NrrdIO's own hand-maintained list.

Verification (local, BRAINSTools against ITK main)

BRAINSTools 767ba471 built against ITK main, this change the only variable:

check	before	after
libITKNrrdIO-6.0.a main() definitions	1	0
ImageCalculatorUtilsGTest --gtest_list_tests	Teem demoIO banner	Running main() from gtest_main.cc, 16 tests
registered tests (ctest -N)	396	413 — matches ITK 5.4.6 exactly

Found by a downstream build testbed that builds ITK consumers against a changed ITK; not visible to ITK's own CI, which does not build BRAINSTools' GTest suite.

[dzenanz]

This problem is hilarious, despite being real.

[greptile-apps]

Greptile Summary

This PR removes the NrrdIO demo source from the library build. The main changes are:

• Drops sampleIO.c from nrrdio_SRCS in Modules/ThirdParty/NrrdIO/src/NrrdIO/CMakeLists.txt.
• Keeps the vendored CMake library source list aligned with NrrdIO_Srcs.txt.
• Prevents the sampleIO demo program's main() from being compiled into ITKNrrdIO.

Confidence Score: 5/5

This PR is safe to merge with minimal risk.

The change is a one-line removal from a vendored CMake source list, and the surrounding vendored metadata confirms sampleIO.c is a standalone demo executable source rather than library code.

No files require special attention.

T-Rex Logs

What T-Rex did

• The T-Rex reviewer examined the general contract validation proof set, noting the build-time transcripts and tool state, static validation findings about sampleIO.c, and the GNUmake dry-run results showing the library and sampleIO compilation order.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
Modules/ThirdParty/NrrdIO/src/NrrdIO/CMakeLists.txt	Removes sampleIO.c from the NrrdIO library source list so the vendored library no longer compiles the demo program's main() into ITKNrrdIO.

_{Reviews (1): Last reviewed commit: "BUG: Do not compile NrrdIO's sampleIO.c ..." | Re-trigger Greptile}