Compensate for Windows filesystems lacking junction support#27598
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virtiofs lacking junction support
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I'm supportive of this PR, but note that #17192 appears to be a different issue (that's an error in |
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virtiofs lacking junction support**Problem:** Bazel fails completely on Windows when using filesystems that don't support junction/reparse point operations (e.g., virtiofs, VirtualBox shared folders, network drives, RAM disks). The fatal error occurs when `ReadSymlinkOrJunction` fails during path resolution (e.g., when Starlark code calls `.realpath`): "Cannot read link: DeviceIoControl: Incorrect function" This causes build analysis to abort completely. Additionally, `CreateJunction` failures when creating convenience symlinks produce cryptic error messages, though these were already non-fatal warnings. Both fail because `DeviceIoControl` returns `ERROR_INVALID_FUNCTION` when the filesystem doesn't implement `FSCTL_GET_REPARSE_POINT` or `FSCTL_SET_REPARSE_POINT` operations. **Solution:** Handle `ERROR_INVALID_FUNCTION` gracefully by treating it as a "not supported" condition rather than a fatal error: 1. in `ReadSymlinkOrJunction` (`file.cc`:592): return `kNotALink` instead of `kError` when `ERROR_INVALID_FUNCTION` occurs. This allows path resolution to continue for non-symlink paths on unsupported filesystems. 2. in `CreateJunction` (`file.cc`:461): return new `kNotSupported` result code when `ERROR_INVALID_FUNCTION` occurs. This produces clearer "filesystem does not support junctions" warnings instead of cryptic "Incorrect function" messages. This improves UX but doesn't change behavior (these failures were already non-fatal). This follows the try-first, fallback-on-error pattern (EAFP) used by other major projects when handling unsupported filesystem operations. **Prior art:** - Rust (rust-lang/rust#138133): checks `ERROR_INVALID_FUNCTION`, `ERROR_NOT_SUPPORTED`, and `ERROR_INVALID_PARAMETER` for filesystem operation fallbacks in `std::fs::rename`. - Microsoft STL (microsoft/STL#2077): handles junctions and reparse point errors including `ERROR_INVALID_PARAMETER` with robust fallback logic in `filesystem.cpp`. - Go (golang/go#20506): uses fallback strategies when symlink APIs are unavailable on different Windows versions. - WinFsp (winfsp/winfsp#88): documents that `ERROR_INVALID_FUNCTION` indicates `STATUS_NOT_IMPLEMENTED` for unsupported operations. - Microsoft Learn: recommends checking `FILE_SUPPORTS_REPARSE_POINTS` flag via `GetVolumeInformation`, but try-catch approach is simpler and handles edge cases where detection succeeds but operations fail. **Impact:** - enables Bazel builds on virtiofs, VirtualBox shared folders, RAM disks, and other filesystems that don't support Windows junction operations. - convenience symlinks (bazel-bin, bazel-out, etc.) still won't be created, but now with clearer error messages. **Limitations:** Full junction support would require filesystem-level changes (e.g., virtiofs driver improvements). **Testing:** Tested on Windows 11 VM with host directory mounted via virtiofs, with [rules_pkg](https://github.com/bazelbuild/rules_pkg/blob/6cdaba69ee76463b2b8e97e8d243dbb6115c3aee/toolchains/git/git_configure.bzl#L40). Before change: build analysis aborted with "Cannot read link" fatal error. After change: builds complete successfully with clearer warnings about unsupported junctions for convenience symlinks.
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@bazel-io fork 9.0.0 |
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**Problem**: Bazel fails completely on Windows when using filesystems that don't support junction/reparse point operations (e.g., virtiofs, VirtualBox shared folders, network drives, RAM disks). The fatal error occurs when `ReadSymlinkOrJunction` fails during path resolution (e.g., when Starlark code calls `.realpath`): "Cannot read link: DeviceIoControl: Incorrect function". This causes build analysis to abort completely. Additionally, `CreateJunction` failures when creating convenience symlinks produce cryptic error messages, though these were already non-fatal warnings. Both fail because `DeviceIoControl` returns `ERROR_INVALID_FUNCTION` when the filesystem doesn't implement `FSCTL_GET_REPARSE_POINT` or `FSCTL_SET_REPARSE_POINT` operations. **Proposed solution:** Handle `ERROR_INVALID_FUNCTION` gracefully by treating it as a "not supported" condition rather than a fatal error: 1. in `ReadSymlinkOrJunction` (`file.cc`:592): return `kNotALink` instead of `kError` when `ERROR_INVALID_FUNCTION` occurs. This allows path resolution to continue for non-symlink paths on unsupported filesystems. 2. in `CreateJunction` (`file.cc`:461): return new `kNotSupported` result code when `ERROR_INVALID_FUNCTION` occurs. This produces clear "filesystem does not support junctions" warnings instead of cryptic "Incorrect function" messages. This improves UX but doesn't change behavior (these failures were already non-fatal). This follows the try-first, fallback-on-error pattern (EAFP) used by other major projects when handling unsupported filesystem operations. **Prior art:** - Rust (rust-lang/rust#138133): checks `ERROR_INVALID_FUNCTION`, `ERROR_NOT_SUPPORTED`, and `ERROR_INVALID_PARAMETER` for filesystem operation fallbacks in `std::fs::rename`. - Microsoft STL (microsoft/STL#2077): handles junctions and reparse point errors including `ERROR_INVALID_PARAMETER` with robust fallback logic in `filesystem.cpp`. - Go (golang/go#20506): uses fallback strategies when symlink APIs are unavailable on different Windows versions. - WinFsp (winfsp/winfsp#88): documents that `ERROR_INVALID_FUNCTION` indicates `STATUS_NOT_IMPLEMENTED` for unsupported operations. - Microsoft Learn: recommends checking `FILE_SUPPORTS_REPARSE_POINTS` flag via `GetVolumeInformation`, but try-catch approach is simpler and handles edge cases where detection succeeds but operations fail. **Impact**: - enables Bazel to work on virtiofs, VirtualBox shared folders, RAM disks, and other filesystems that don't support Windows junction operations. - convenience symlinks (bazel-bin, bazel-out, etc.) still won't be created, but now with clearer error messages. **Limitations**: Full junction support would require filesystem-level changes (e.g., virtiofs driver improvements). **Testing:** Tested on Windows 11 VM with host directory mounted via virtiofs, with [rules_pkg](https://github.com/bazelbuild/rules_pkg/blob/6cdaba69ee76463b2b8e97e8d243dbb6115c3aee/toolchains/git/git_configure.bzl#L40). Before change: build analysis aborted with "Cannot read link" fatal error. After change: builds complete successfully with clearer warnings about unsupported junctions for convenience symlinks. Closes bazelbuild#27598. PiperOrigin-RevId: 833360316 Change-Id: I3751602b2bd793c1cee75b7b66fa73c955a72517
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…27695) **Problem**: Bazel fails completely on Windows when using filesystems that don't support junction/reparse point operations (e.g., virtiofs, VirtualBox shared folders, network drives, RAM disks). The fatal error occurs when `ReadSymlinkOrJunction` fails during path resolution (e.g., when Starlark code calls `.realpath`): "Cannot read link: DeviceIoControl: Incorrect function". This causes build analysis to abort completely. Additionally, `CreateJunction` failures when creating convenience symlinks produce cryptic error messages, though these were already non-fatal warnings. Both fail because `DeviceIoControl` returns `ERROR_INVALID_FUNCTION` when the filesystem doesn't implement `FSCTL_GET_REPARSE_POINT` or `FSCTL_SET_REPARSE_POINT` operations. **Proposed solution:** Handle `ERROR_INVALID_FUNCTION` gracefully by treating it as a "not supported" condition rather than a fatal error: 1. in `ReadSymlinkOrJunction` (`file.cc`:592): return `kNotALink` instead of `kError` when `ERROR_INVALID_FUNCTION` occurs. This allows path resolution to continue for non-symlink paths on unsupported filesystems. 2. in `CreateJunction` (`file.cc`:461): return new `kNotSupported` result code when `ERROR_INVALID_FUNCTION` occurs. This produces clear "filesystem does not support junctions" warnings instead of cryptic "Incorrect function" messages. This improves UX but doesn't change behavior (these failures were already non-fatal). This follows the try-first, fallback-on-error pattern (EAFP) used by other major projects when handling unsupported filesystem operations. **Prior art:** - Rust (rust-lang/rust#138133): checks `ERROR_INVALID_FUNCTION`, `ERROR_NOT_SUPPORTED`, and `ERROR_INVALID_PARAMETER` for filesystem operation fallbacks in `std::fs::rename`. - Microsoft STL (microsoft/STL#2077): handles junctions and reparse point errors including `ERROR_INVALID_PARAMETER` with robust fallback logic in `filesystem.cpp`. - Go (golang/go#20506): uses fallback strategies when symlink APIs are unavailable on different Windows versions. - WinFsp (winfsp/winfsp#88): documents that `ERROR_INVALID_FUNCTION` indicates `STATUS_NOT_IMPLEMENTED` for unsupported operations. - Microsoft Learn: recommends checking `FILE_SUPPORTS_REPARSE_POINTS` flag via `GetVolumeInformation`, but try-catch approach is simpler and handles edge cases where detection succeeds but operations fail. **Impact**: - enables Bazel to work on virtiofs, VirtualBox shared folders, RAM disks, and other filesystems that don't support Windows junction operations. - convenience symlinks (bazel-bin, bazel-out, etc.) still won't be created, but now with clearer error messages. **Limitations**: Full junction support would require filesystem-level changes (e.g., virtiofs driver improvements). **Testing:** Tested on Windows 11 VM with host directory mounted via virtiofs, with [rules_pkg](https://github.com/bazelbuild/rules_pkg/blob/6cdaba69ee76463b2b8e97e8d243dbb6115c3aee/toolchains/git/git_configure.bzl#L40). Before change: build analysis aborted with "Cannot read link" fatal error. After change: builds complete successfully with clearer warnings about unsupported junctions for convenience symlinks. Closes #27598. PiperOrigin-RevId: 833360316 Change-Id: I3751602b2bd793c1cee75b7b66fa73c955a72517 Commit dab96fc Co-authored-by: Rgis Desgroppes <[email protected]>
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The changes in this PR have been included in Bazel 9.0.0 RC3. Please test out the release candidate and report any issues as soon as possible. |
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**Problem**: Bazel fails completely on Windows when using filesystems that don't support junction/reparse point operations (e.g., virtiofs, VirtualBox shared folders, network drives, RAM disks). The fatal error occurs when `ReadSymlinkOrJunction` fails during path resolution (e.g., when Starlark code calls `.realpath`): "Cannot read link: DeviceIoControl: Incorrect function". This causes build analysis to abort completely. Additionally, `CreateJunction` failures when creating convenience symlinks produce cryptic error messages, though these were already non-fatal warnings. Both fail because `DeviceIoControl` returns `ERROR_INVALID_FUNCTION` when the filesystem doesn't implement `FSCTL_GET_REPARSE_POINT` or `FSCTL_SET_REPARSE_POINT` operations. **Proposed solution:** Handle `ERROR_INVALID_FUNCTION` gracefully by treating it as a "not supported" condition rather than a fatal error: 1. in `ReadSymlinkOrJunction` (`file.cc`:592): return `kNotALink` instead of `kError` when `ERROR_INVALID_FUNCTION` occurs. This allows path resolution to continue for non-symlink paths on unsupported filesystems. 2. in `CreateJunction` (`file.cc`:461): return new `kNotSupported` result code when `ERROR_INVALID_FUNCTION` occurs. This produces clear "filesystem does not support junctions" warnings instead of cryptic "Incorrect function" messages. This improves UX but doesn't change behavior (these failures were already non-fatal). This follows the try-first, fallback-on-error pattern (EAFP) used by other major projects when handling unsupported filesystem operations. **Prior art:** - Rust (rust-lang/rust#138133): checks `ERROR_INVALID_FUNCTION`, `ERROR_NOT_SUPPORTED`, and `ERROR_INVALID_PARAMETER` for filesystem operation fallbacks in `std::fs::rename`. - Microsoft STL (microsoft/STL#2077): handles junctions and reparse point errors including `ERROR_INVALID_PARAMETER` with robust fallback logic in `filesystem.cpp`. - Go (golang/go#20506): uses fallback strategies when symlink APIs are unavailable on different Windows versions. - WinFsp (winfsp/winfsp#88): documents that `ERROR_INVALID_FUNCTION` indicates `STATUS_NOT_IMPLEMENTED` for unsupported operations. - Microsoft Learn: recommends checking `FILE_SUPPORTS_REPARSE_POINTS` flag via `GetVolumeInformation`, but try-catch approach is simpler and handles edge cases where detection succeeds but operations fail. **Impact**: - enables Bazel to work on virtiofs, VirtualBox shared folders, RAM disks, and other filesystems that don't support Windows junction operations. - convenience symlinks (bazel-bin, bazel-out, etc.) still won't be created, but now with clearer error messages. **Limitations**: Full junction support would require filesystem-level changes (e.g., virtiofs driver improvements). **Testing:** Tested on Windows 11 VM with host directory mounted via virtiofs, with [rules_pkg](https://github.com/bazelbuild/rules_pkg/blob/6cdaba69ee76463b2b8e97e8d243dbb6115c3aee/toolchains/git/git_configure.bzl#L40). Before change: build analysis aborted with "Cannot read link" fatal error. After change: builds complete successfully with clearer warnings about unsupported junctions for convenience symlinks. Closes bazelbuild#27598. PiperOrigin-RevId: 833360316 Change-Id: I3751602b2bd793c1cee75b7b66fa73c955a72517 (cherry-picked from commit dab96fc)
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Jan 20, 2026
**Problem**: Bazel fails completely on Windows when using filesystems that don't support junction/reparse point operations (e.g., virtiofs, VirtualBox shared folders, network drives, RAM disks). The fatal error occurs when `ReadSymlinkOrJunction` fails during path resolution (e.g., when Starlark code calls `.realpath`): "Cannot read link: DeviceIoControl: Incorrect function". This causes build analysis to abort completely. Additionally, `CreateJunction` failures when creating convenience symlinks produce cryptic error messages, though these were already non-fatal warnings. Both fail because `DeviceIoControl` returns `ERROR_INVALID_FUNCTION` when the filesystem doesn't implement `FSCTL_GET_REPARSE_POINT` or `FSCTL_SET_REPARSE_POINT` operations. **Proposed solution:** Handle `ERROR_INVALID_FUNCTION` gracefully by treating it as a "not supported" condition rather than a fatal error: 1. in `ReadSymlinkOrJunction` (`file.cc`:592): return `kNotALink` instead of `kError` when `ERROR_INVALID_FUNCTION` occurs. This allows path resolution to continue for non-symlink paths on unsupported filesystems. 2. in `CreateJunction` (`file.cc`:461): return new `kNotSupported` result code when `ERROR_INVALID_FUNCTION` occurs. This produces clear "filesystem does not support junctions" warnings instead of cryptic "Incorrect function" messages. This improves UX but doesn't change behavior (these failures were already non-fatal). This follows the try-first, fallback-on-error pattern (EAFP) used by other major projects when handling unsupported filesystem operations. **Prior art:** - Rust (rust-lang/rust#138133): checks `ERROR_INVALID_FUNCTION`, `ERROR_NOT_SUPPORTED`, and `ERROR_INVALID_PARAMETER` for filesystem operation fallbacks in `std::fs::rename`. - Microsoft STL (microsoft/STL#2077): handles junctions and reparse point errors including `ERROR_INVALID_PARAMETER` with robust fallback logic in `filesystem.cpp`. - Go (golang/go#20506): uses fallback strategies when symlink APIs are unavailable on different Windows versions. - WinFsp (winfsp/winfsp#88): documents that `ERROR_INVALID_FUNCTION` indicates `STATUS_NOT_IMPLEMENTED` for unsupported operations. - Microsoft Learn: recommends checking `FILE_SUPPORTS_REPARSE_POINTS` flag via `GetVolumeInformation`, but try-catch approach is simpler and handles edge cases where detection succeeds but operations fail. **Impact**: - enables Bazel to work on virtiofs, VirtualBox shared folders, RAM disks, and other filesystems that don't support Windows junction operations. - convenience symlinks (bazel-bin, bazel-out, etc.) still won't be created, but now with clearer error messages. **Limitations**: Full junction support would require filesystem-level changes (e.g., virtiofs driver improvements). **Testing:** Tested on Windows 11 VM with host directory mounted via virtiofs, with [rules_pkg](https://github.com/bazelbuild/rules_pkg/blob/6cdaba69ee76463b2b8e97e8d243dbb6115c3aee/toolchains/git/git_configure.bzl#L40). Before change: build analysis aborted with "Cannot read link" fatal error. After change: builds complete successfully with clearer warnings about unsupported junctions for convenience symlinks. Closes bazelbuild#27598. PiperOrigin-RevId: 833360316 Change-Id: I3751602b2bd793c1cee75b7b66fa73c955a72517 (cherry-picked from commit dab96fc)
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@bazel-io fork 8.6.0 |
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**Problem**: Bazel fails completely on Windows when using filesystems that don't support junction/reparse point operations (e.g., virtiofs, VirtualBox shared folders, network drives, RAM disks). The fatal error occurs when `ReadSymlinkOrJunction` fails during path resolution (e.g., when Starlark code calls `.realpath`): "Cannot read link: DeviceIoControl: Incorrect function". This causes build analysis to abort completely. Additionally, `CreateJunction` failures when creating convenience symlinks produce cryptic error messages, though these were already non-fatal warnings. Both fail because `DeviceIoControl` returns `ERROR_INVALID_FUNCTION` when the filesystem doesn't implement `FSCTL_GET_REPARSE_POINT` or `FSCTL_SET_REPARSE_POINT` operations. **Proposed solution:** Handle `ERROR_INVALID_FUNCTION` gracefully by treating it as a "not supported" condition rather than a fatal error: 1. in `ReadSymlinkOrJunction` (`file.cc`:592): return `kNotALink` instead of `kError` when `ERROR_INVALID_FUNCTION` occurs. This allows path resolution to continue for non-symlink paths on unsupported filesystems. 2. in `CreateJunction` (`file.cc`:461): return new `kNotSupported` result code when `ERROR_INVALID_FUNCTION` occurs. This produces clear "filesystem does not support junctions" warnings instead of cryptic "Incorrect function" messages. This improves UX but doesn't change behavior (these failures were already non-fatal). This follows the try-first, fallback-on-error pattern (EAFP) used by other major projects when handling unsupported filesystem operations. **Prior art:** - Rust (rust-lang/rust#138133): checks `ERROR_INVALID_FUNCTION`, `ERROR_NOT_SUPPORTED`, and `ERROR_INVALID_PARAMETER` for filesystem operation fallbacks in `std::fs::rename`. - Microsoft STL (microsoft/STL#2077): handles junctions and reparse point errors including `ERROR_INVALID_PARAMETER` with robust fallback logic in `filesystem.cpp`. - Go (golang/go#20506): uses fallback strategies when symlink APIs are unavailable on different Windows versions. - WinFsp (winfsp/winfsp#88): documents that `ERROR_INVALID_FUNCTION` indicates `STATUS_NOT_IMPLEMENTED` for unsupported operations. - Microsoft Learn: recommends checking `FILE_SUPPORTS_REPARSE_POINTS` flag via `GetVolumeInformation`, but try-catch approach is simpler and handles edge cases where detection succeeds but operations fail. **Impact**: - enables Bazel to work on virtiofs, VirtualBox shared folders, RAM disks, and other filesystems that don't support Windows junction operations. - convenience symlinks (bazel-bin, bazel-out, etc.) still won't be created, but now with clearer error messages. **Limitations**: Full junction support would require filesystem-level changes (e.g., virtiofs driver improvements). **Testing:** Tested on Windows 11 VM with host directory mounted via virtiofs, with [rules_pkg](https://github.com/bazelbuild/rules_pkg/blob/6cdaba69ee76463b2b8e97e8d243dbb6115c3aee/toolchains/git/git_configure.bzl#L40). Before change: build analysis aborted with "Cannot read link" fatal error. After change: builds complete successfully with clearer warnings about unsupported junctions for convenience symlinks. Closes bazelbuild#27598. PiperOrigin-RevId: 833360316 Change-Id: I3751602b2bd793c1cee75b7b66fa73c955a72517
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…28367) **Problem**: Bazel fails completely on Windows when using filesystems that don't support junction/reparse point operations (e.g., virtiofs, VirtualBox shared folders, network drives, RAM disks). The fatal error occurs when `ReadSymlinkOrJunction` fails during path resolution (e.g., when Starlark code calls `.realpath`): "Cannot read link: DeviceIoControl: Incorrect function". This causes build analysis to abort completely. Additionally, `CreateJunction` failures when creating convenience symlinks produce cryptic error messages, though these were already non-fatal warnings. Both fail because `DeviceIoControl` returns `ERROR_INVALID_FUNCTION` when the filesystem doesn't implement `FSCTL_GET_REPARSE_POINT` or `FSCTL_SET_REPARSE_POINT` operations. **Proposed solution:** Handle `ERROR_INVALID_FUNCTION` gracefully by treating it as a "not supported" condition rather than a fatal error: 1. in `ReadSymlinkOrJunction` (`file.cc`:592): return `kNotALink` instead of `kError` when `ERROR_INVALID_FUNCTION` occurs. This allows path resolution to continue for non-symlink paths on unsupported filesystems. 2. in `CreateJunction` (`file.cc`:461): return new `kNotSupported` result code when `ERROR_INVALID_FUNCTION` occurs. This produces clear "filesystem does not support junctions" warnings instead of cryptic "Incorrect function" messages. This improves UX but doesn't change behavior (these failures were already non-fatal). This follows the try-first, fallback-on-error pattern (EAFP) used by other major projects when handling unsupported filesystem operations. **Prior art:** - Rust (rust-lang/rust#138133): checks `ERROR_INVALID_FUNCTION`, `ERROR_NOT_SUPPORTED`, and `ERROR_INVALID_PARAMETER` for filesystem operation fallbacks in `std::fs::rename`. - Microsoft STL (microsoft/STL#2077): handles junctions and reparse point errors including `ERROR_INVALID_PARAMETER` with robust fallback logic in `filesystem.cpp`. - Go (golang/go#20506): uses fallback strategies when symlink APIs are unavailable on different Windows versions. - WinFsp (winfsp/winfsp#88): documents that `ERROR_INVALID_FUNCTION` indicates `STATUS_NOT_IMPLEMENTED` for unsupported operations. - Microsoft Learn: recommends checking `FILE_SUPPORTS_REPARSE_POINTS` flag via `GetVolumeInformation`, but try-catch approach is simpler and handles edge cases where detection succeeds but operations fail. **Impact**: - enables Bazel to work on virtiofs, VirtualBox shared folders, RAM disks, and other filesystems that don't support Windows junction operations. - convenience symlinks (bazel-bin, bazel-out, etc.) still won't be created, but now with clearer error messages. **Limitations**: Full junction support would require filesystem-level changes (e.g., virtiofs driver improvements). **Testing:** Tested on Windows 11 VM with host directory mounted via virtiofs, with [rules_pkg](https://github.com/bazelbuild/rules_pkg/blob/6cdaba69ee76463b2b8e97e8d243dbb6115c3aee/toolchains/git/git_configure.bzl#L40). Before change: build analysis aborted with "Cannot read link" fatal error. After change: builds complete successfully with clearer warnings about unsupported junctions for convenience symlinks. Closes #27598. PiperOrigin-RevId: 833360316 Change-Id: I3751602b2bd793c1cee75b7b66fa73c955a72517 Commit dab96fc Co-authored-by: Rgis Desgroppes <[email protected]>
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…28367) **Problem**: Bazel fails completely on Windows when using filesystems that don't support junction/reparse point operations (e.g., virtiofs, VirtualBox shared folders, network drives, RAM disks). The fatal error occurs when `ReadSymlinkOrJunction` fails during path resolution (e.g., when Starlark code calls `.realpath`): "Cannot read link: DeviceIoControl: Incorrect function". This causes build analysis to abort completely. Additionally, `CreateJunction` failures when creating convenience symlinks produce cryptic error messages, though these were already non-fatal warnings. Both fail because `DeviceIoControl` returns `ERROR_INVALID_FUNCTION` when the filesystem doesn't implement `FSCTL_GET_REPARSE_POINT` or `FSCTL_SET_REPARSE_POINT` operations. **Proposed solution:** Handle `ERROR_INVALID_FUNCTION` gracefully by treating it as a "not supported" condition rather than a fatal error: 1. in `ReadSymlinkOrJunction` (`file.cc`:592): return `kNotALink` instead of `kError` when `ERROR_INVALID_FUNCTION` occurs. This allows path resolution to continue for non-symlink paths on unsupported filesystems. 2. in `CreateJunction` (`file.cc`:461): return new `kNotSupported` result code when `ERROR_INVALID_FUNCTION` occurs. This produces clear "filesystem does not support junctions" warnings instead of cryptic "Incorrect function" messages. This improves UX but doesn't change behavior (these failures were already non-fatal). This follows the try-first, fallback-on-error pattern (EAFP) used by other major projects when handling unsupported filesystem operations. **Prior art:** - Rust (rust-lang/rust#138133): checks `ERROR_INVALID_FUNCTION`, `ERROR_NOT_SUPPORTED`, and `ERROR_INVALID_PARAMETER` for filesystem operation fallbacks in `std::fs::rename`. - Microsoft STL (microsoft/STL#2077): handles junctions and reparse point errors including `ERROR_INVALID_PARAMETER` with robust fallback logic in `filesystem.cpp`. - Go (golang/go#20506): uses fallback strategies when symlink APIs are unavailable on different Windows versions. - WinFsp (winfsp/winfsp#88): documents that `ERROR_INVALID_FUNCTION` indicates `STATUS_NOT_IMPLEMENTED` for unsupported operations. - Microsoft Learn: recommends checking `FILE_SUPPORTS_REPARSE_POINTS` flag via `GetVolumeInformation`, but try-catch approach is simpler and handles edge cases where detection succeeds but operations fail. **Impact**: - enables Bazel to work on virtiofs, VirtualBox shared folders, RAM disks, and other filesystems that don't support Windows junction operations. - convenience symlinks (bazel-bin, bazel-out, etc.) still won't be created, but now with clearer error messages. **Limitations**: Full junction support would require filesystem-level changes (e.g., virtiofs driver improvements). **Testing:** Tested on Windows 11 VM with host directory mounted via virtiofs, with [rules_pkg](https://github.com/bazelbuild/rules_pkg/blob/6cdaba69ee76463b2b8e97e8d243dbb6115c3aee/toolchains/git/git_configure.bzl#L40). Before change: build analysis aborted with "Cannot read link" fatal error. After change: builds complete successfully with clearer warnings about unsupported junctions for convenience symlinks. Closes #27598. PiperOrigin-RevId: 833360316 Change-Id: I3751602b2bd793c1cee75b7b66fa73c955a72517 Commit dab96fc Co-authored-by: Rgis Desgroppes <[email protected]>
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Problem:
Bazel fails completely on Windows when using filesystems that don't support junction/reparse point operations (e.g., virtiofs, VirtualBox shared folders, network drives, RAM disks).
The fatal error occurs when
ReadSymlinkOrJunctionfails during path resolution (e.g., when Starlark code calls.realpath): "Cannot read link: DeviceIoControl: Incorrect function".This causes build analysis to abort completely.
Additionally,
CreateJunctionfailures when creating convenience symlinks produce cryptic error messages, though these were already non-fatal warnings.Both fail because
DeviceIoControlreturnsERROR_INVALID_FUNCTIONwhen the filesystem doesn't implementFSCTL_GET_REPARSE_POINTorFSCTL_SET_REPARSE_POINToperations.Proposed solution:
Handle
ERROR_INVALID_FUNCTIONgracefully by treating it as a "not supported" condition rather than a fatal error:ReadSymlinkOrJunction(file.cc:592): returnkNotALinkinstead ofkErrorwhenERROR_INVALID_FUNCTIONoccurs. This allows path resolution to continue for non-symlink paths on unsupported filesystems.CreateJunction(file.cc:461): return newkNotSupportedresult code whenERROR_INVALID_FUNCTIONoccurs. This produces clear "filesystem does not support junctions" warnings instead of cryptic "Incorrect function" messages. This improves UX but doesn't change behavior (these failures were already non-fatal).This follows the try-first, fallback-on-error pattern (EAFP) used by other major projects when handling unsupported filesystem operations.
Prior art:
ERROR_INVALID_FUNCTION,ERROR_NOT_SUPPORTED, andERROR_INVALID_PARAMETERfor filesystem operation fallbacks instd::fs::rename.<filesystem>:read_symlinkdoes not work with junctions microsoft/STL#2077): handles junctions and reparse point errors includingERROR_INVALID_PARAMETERwith robust fallback logic infilesystem.cpp.ERROR_INVALID_FUNCTIONindicatesSTATUS_NOT_IMPLEMENTEDfor unsupported operations.FILE_SUPPORTS_REPARSE_POINTSflag viaGetVolumeInformation, but try-catch approach is simpler and handles edge cases where detection succeeds but operations fail.Impact:
Limitations:
Full junction support would require filesystem-level changes (e.g., virtiofs driver improvements).
Testing:
Tested on Windows 11 VM with host directory mounted via virtiofs, with rules_pkg. Before change: build analysis aborted with "Cannot read link" fatal error. After change: builds complete successfully with clearer warnings about unsupported junctions for convenience symlinks.