BUG: Use check_symbol_exists for TIFFFieldReadCount detection

[blowekamp]

Summary

Fixes #6148.

When building with a system TIFF library (ITK_USE_SYSTEM_TIFF=ON), the CMake check for TIFFFieldReadCount used check_type_size(), which internally calls sizeof() on the argument. Passing a function name to sizeof() is non-standard — GCC and Clang accept it as an extension but MSVC rejects it — so ITK_TIFF_HAS_TIFFFieldReadCount was never defined on Windows builds using an external libTIFF.

Without that define, itkTIFFImageIO falls through to the libtiff 4.0.0–4.0.2 workaround that directly accesses the internal _TIFFField struct. That struct layout is no longer correct for modern libtiff versions, causing reads of garbage data and NULL pointer crashes when encountering tags with unsupported data types (e.g. an ICC profile tag).

Fix

Replace check_type_size(TIFFFieldReadCount ...) with check_symbol_exists(TIFFFieldReadCount "tiffio.h" ...), which correctly detects the function on all compilers including MSVC.

[dzenanz]

/azp run ITK.macOS

[dzenanz]

LGTM

[hjmjohnson]

@greptile Review this PR.

[greptile-apps]

Greptile Summary

This PR fixes a CMake detection issue for TIFFFieldReadCount when building with a system TIFF library (ITK_USE_SYSTEM_TIFF=ON). The old check_type_size() call applied sizeof() to a function name — non-standard behavior that compiles on GCC/Clang as an extension but fails silently on MSVC, leaving ITK_TIFF_HAS_TIFFFieldReadCount undefined and causing downstream crashes with modern libtiff. The fix correctly replaces it with check_symbol_exists(), which is the proper CMake mechanism for detecting function symbols across all compilers.

Confidence Score: 5/5

Safe to merge — targeted, correct CMake fix with no functional regressions.

The change is minimal and well-reasoned: it swaps one CMake introspection call for the semantically correct one, adds the necessary module include, preserves all surrounding logic, and leaves the check_type_size(TIFFField* …) call (which operates on a real type) untouched. CMAKE_REQUIRED_LIBRARIES is already set before both checks. No issues were found.

No files require special attention.

Important Files Changed

Filename	Overview
Modules/ThirdParty/TIFF/CMakeLists.txt	Replaces check_type_size(TIFFFieldReadCount …) with check_symbol_exists(TIFFFieldReadCount "tiffio.h" …) and adds include(CheckSymbolExists); CMAKE_REQUIRED_LIBRARIES and the check_type_size(TIFFField* …) call are left intact and correct.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[CMake configure with ITK_USE_SYSTEM_TIFF=ON] --> B[find_package TIFF::TIFF]
    B --> C[include CheckSymbolExists]
    C --> D["check_symbol_exists(TIFFFieldReadCount tiffio.h ...)"]
    D -->|Symbol found| E[ITK_TIFF_HAS_TIFFFieldReadCount = 1]
    D -->|Symbol not found| F[ITK_TIFF_HAS_TIFFFieldReadCount unset]
    E --> G[check_type_size TIFFField*]
    F --> G
    G --> H[configure_file itk_tiff.h.in → itk_tiff.h]
    H -->|ITK_TIFF_HAS_TIFFFieldReadCount defined| I[itkTIFFImageIO uses TIFFFieldReadCount API]
    H -->|Not defined| J[itkTIFFImageIO falls back to legacy _TIFFField struct access → crashes with modern libtiff]

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_{Reviews (2): Last reviewed commit: "BUG: Use check_symbol_exists for TIFFFie..." | Re-trigger Greptile}