Filter std:: instantiations out of Halide.dll's export list

[alexreinking]

CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS exports every external symbol in Halide's object files, including COMDAT instantiations of std:: templates (e.g. std::vector<Halide::Func>::~vector). The windows-32 (MSVC x86) job is just under link.exe's 65535-export limit on main; #9486 adds one source file and trips LNK1189: library limit of 65535 objects exceeded.

For MSVC shared builds only, Halide now turns off WINDOWS_EXPORT_ALL_SYMBOLS and instead:

1. writes its object list (including Halide_initmod) with file(GENERATE) from $<TARGET_OBJECTS>,
2. runs cmake -E __create_def as a PRE_LINK step — the same internal command CMake uses for export-all — to produce the full .def,
3. runs a CMake script, cmake/FilterDllExports.cmake, which drops symbols whose outermost enclosing scope is std, stdext, Concurrency, llvm or clang, and
4. links with /DEF:<filtered.def>.

The filter reads the enclosing scope from the MSVC mangling rather than matching substrings, since Halide functions taking std::string also contain @std@@. Anything it can't parse confidently is kept, as are C symbols (halide_*) and everything in Halide::. Consumers instantiate their own copies of std templates, so they don't need them from the DLL. Template argument lists without nested templates are a regular language, so the script repeatedly collapses innermost ?$name@args@ template-ids with a regex until the qualified name is flat, then reads its outermost scope — no character loops (~4 s on 65k synthetic symbols). Export counts are reported only at --log-level=VERBOSE; it warns above 95% of the limit and fails with a clear error (instead of LNK1189) above it. clang-cl, non-Windows and static builds are unchanged.

Checklist

• Tests added or updated (not required for docs, CI config, or typo fixes)
• Documentation updated (if public API changed)
• Python bindings updated (if public API changed)
• Benchmarks are included here if the change is intended to affect performance.
• Commits include AI attribution where applicable (see Code of Conduct)

Validation: the new filter_dll_exports ctest (runs the script on 41 hand-written mangled names vs. expected output) passes on macOS; the Halide target configures and builds on macOS with the non-Windows path unchanged; forcing the MSVC branch on and inspecting build.ninja showed the PRE_LINK command and /DEF: flag on the link step.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.87%. Comparing base (95127ea) to head (a505414).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9489      +/-   ##
==========================================
+ Coverage   70.77%   70.87%   +0.10%     
==========================================
  Files         261      261              
  Lines       79989    79989              
  Branches    19494    19494              
==========================================
+ Hits        56612    56696      +84     
+ Misses      17487    17451      -36     
+ Partials     5890     5842      -48     

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[derek-gerstmann]

Oh man ... good find! We definitely don't want all of std:: !!