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….def on MSVC The generated module-definition file already exports, and therefore keeps, every symbol. The redundant /INCLUDE flags exceed the 32,767 character Windows command-line limit for thousands of symbols. Also stop naming the DLL MyDLL in the generated module-definition file.
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #3713 +/- ##
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Coverage 87.89% 87.89%
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Files 310 310
Lines 19771 19772 +1
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+ Hits 17377 17378 +1
Misses 2394 2394
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mosuem
marked this pull request as ready for review
September 30, 2026 12:30
This was referenced Sep 30, 2026
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Description
On Windows,
LinkerOptions.treeshakepasses an/INCLUDE:<symbol>flag per kept symbol and a generated module-definition (.def) file that exports the same symbols. TheEXPORTSin the.deffile already makelink.exeresolve (pull in from the archive) and keep every symbol, so the/INCLUDE:flags are redundant.They are also harmful for large APIs: with thousands of symbols (e.g. BoringSSL or ICU4X bindings), the flags exceed the 32,767 character command-line limit of Windows and the link fails. Packages such as
package:boringcurrently work around this by parsing the COFF archive and writing their own.deffile withLinkerOptions.manual. With this change,LinkerOptions.treeshakeworks for them directly.Changes:
/INCLUDE:flags forcl.exewhen the.deffile is generated (LinkerOptions.treeshakewith non-nullsymbolsToKeep).LinkerOptions.manualis unchanged.LIBRARY MyDLLplaceholder (and the trailing whitespace) from the generated.deffile, so the DLL name comes from/OUTinstead of a mismatchingMyDLL(LNK4070).treeshake_many_symbols_test.dart, which keeps 1,500 of 2,000 long-named plain C functions (without__declspec(dllexport)), i.e. ~110K characters of/INCLUDE:flags before this change.The existing
windows_module_definition_test.dart(and its cross variant for ia32/arm64) already covers that the generated.defalone pulls in a non-exported function from the archive; this PR relies on Windows CI for that, as I only ran the tests on Linux locally.Not included (possible follow-ups): skipping requested symbols that the archive doesn't define (both
/INCLUDE:and.defexports fail with LNK2001 for those;package:boringfilters them via the COFF symbol table).Related Issues
None filed.
PR Checklist
dart tool/ci.dart --alllocally and resolved all issues identified. (Randart formatanddart analyze --fatal-infosonpkgs/native_toolchain_c.)CHANGELOG.mdfor the relevant packages.0.19.6-wip.)