Specify unlink-file-at in terms of POSIX. #852
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Unfortunately only MacOS has the POSIX behavior of returning EPERM when unlinking a directory; Linux returns EISDIR, and Windows returns EACCESS. Because EACCESS may arise for other reasons but which are outside the purview of WASI, we map all EACCESS to EPERM.
wingo
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When attempting to unlink a directory, POSIX specifies the result should be EPERM, but only MacOS implements that behavior. Paper over the differences. Also turn EACCESS into EPERM, to paper over Windows differences. Related to WebAssembly/WASI#852 and WebAssembly/wasi-testsuite#137. POSIX 2008 reference: https://pubs.opengroup.org/onlinepubs/9699919799/functions/unlink.html
wingo
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wingo
added a commit
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Dec 16, 2025
When attempting to unlink a directory, POSIX specifies the result should be EPERM, but only MacOS implements that behavior. Paper over the differences. Also turn EACCESS into EPERM, to paper over Windows differences. Related to WebAssembly/WASI#852 and WebAssembly/wasi-testsuite#137. POSIX 2008 reference: https://pubs.opengroup.org/onlinepubs/9699919799/functions/unlink.html
wingo
added a commit
to wingo/wasmtime
that referenced
this pull request
Dec 16, 2025
When attempting to unlink a directory, POSIX specifies the result should be EPERM, but only MacOS implements that behavior. Paper over the differences. Also turn EACCESS into EPERM, to paper over Windows differences. Related to WebAssembly/WASI#852 and WebAssembly/wasi-testsuite#137. POSIX 2008 reference: https://pubs.opengroup.org/onlinepubs/9699919799/functions/unlink.html
wingo
added a commit
to wingo/wasmtime
that referenced
this pull request
Dec 16, 2025
When attempting to unlink a directory, POSIX specifies the result should be EPERM, but only MacOS implements that behavior. Paper over the differences. Also turn EACCESS into EPERM, to paper over Windows differences. Related to WebAssembly/WASI#852 and WebAssembly/wasi-testsuite#137. POSIX 2008 reference: https://pubs.opengroup.org/onlinepubs/9699919799/functions/unlink.html
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If all major OS flavors return something different, then clearly POSIX is not the authoritative source here. Additionally, the page you referenced includes the footnote:
I personally don't see anything wrong with Linux' behavior of returning EISDIR; it is more to-the-point and precisely describes why it failed, instead of a catch-all EPERM. |
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Ah, thank you for that footnote, I missed it! And I do like Linux's return code! But if we want one semantics, EISDIR isn't it, as we can't translate results from other platforms without races. Another option would be to relax WASI to allow but not require |
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Unfortunately only MacOS has the POSIX behavior of returning EPERM when unlinking a directory; Linux returns EISDIR, and Windows returns EACCESS. Because EACCESS may arise for other reasons but which are outside the purview of WASI, we map all EACCESS to EPERM.