fix: allow rename to overwrite read-only destination on Windows when deduplicating Dune cache by Nevor · Pull Request #13713 · ocaml/dune

Nevor · 2026-03-02T13:59:27Z

In the Dune cache, when a temp artifact already exists in the cache, Dune attempts deduplication by deleting the temp artifact, linking it to the file already in the cache, and then moving the temp artifact to the build directory.

The last step fails on Windows because Dune sets a read-only attribute on the destination file, causing Unix.rename to fail with EACCES in this case. Since the operation fails, Dune does not consider the file cached. Combined with the fact that this seems to happen quite often [1] on Windows, this effectively nullifies the cache speedup.

This PR creates a helper function that removes the read-only attribute on the destination file before trying to overwrite it (similar to the existing win32_unlink) and use it in the deduplication logic of the cache, fixing the issue.

Note: This issue does not exist on Unix. This discrepancy is also being addressed directly on OCaml's side: ocaml/ocaml#14602.

The test dedup.t already exhibits the issue on Windows. The dune_cmd stat hardlinks _build/default/target command returns 1 instead of the expected 3. This PR bumps the result to 2. To make the test completely pass, another issue around Io.portable_hardlink on Windows still needs to be addressed [1].

[1] It seems that the fact that on windows dune always copies files instead of trying to create a hardlink is linked to the fact that this deduplication happen more often on windows. See #13714.

nojb

LGTM

A changes entry (see doc/changes) is in order, since this is an (important!) bug fix on Windows.

otherlibs/stdune/src/fpath.ml

…deduplicating Dune cache In the Dune cache, when a temp artifact already exists in the cache, Dune attempts deduplication by deleting the temp artifact, linking it to the file already in the cache, and then moving the temp artifact to the build directory. The last step fails on Windows because Dune sets a read-only attribute on the destination file, causing Unix.rename to fail with EACCES in this case. Since the operation fails, Dune does not consider the file cached. Combined with the fact that this seems to happen quite often [1] on Windows, this effectively nullifies the cache speedup. This PR creates a helper function that removes the read-only attribute on the destination file before trying to overwrite it (similar to the existing `win32_unlink`) and use it in the deduplication logic of the cache, fixing the issue. Note: This issue does not exist on Unix. This discrepancy is also being addressed directly on OCaml's side: ocaml/ocaml#14602. The test dedup.t already exhibits the issue on Windows. The `dune_cmd stat hardlinks _build/default/target` command returns 1 instead of the expected 3. This PR bumps the result to 2. To make the test completely pass, another issue around `Io.portable_hardlink` on Windows still needs to be addressed [1]. [1] It seems that the fact that on windows dune always copies files instead of trying to create a hardlink is linked to the fact that this deduplication happen more often on windows. Signed-off-by: Roven Lamar Gabriel <nevor@nevor.net>

doc/changes/fixed/13713.md

Signed-off-by: Roven Lamar Gabriel <nevor@nevor.net>

nojb · 2026-03-02T15:54:33Z

There is an OxCaml error in the CI. @Alizter: any insight?

otherlibs/stdune/src/fpath.ml

Co-authored-by: Ali Caglayan <alizter@gmail.com> Signed-off-by: Roven Lamar Gabriel <nevor@nevor.net>

otherlibs/stdune/src/fpath.ml

The `Io.portable_hardlink` function was systematically copying files on Windows instead of trying to create hard links. Hard links have been available for a while on NTFS and have also been available for ReFS for a coupe of years. This availability is not tied to developer mode capabilities (unlike symlinks), which means we can generally expect a Windows environment to be able to create hard links. This PR removes the systematic copy and adds the `EINVAL` error as a fallback signal in case Dune tries to create a hard link on a filesystem that does not support it. The later reduces the risk of a breaking change. Note that a copy fallback could be used when a cross-filesystem link is attempted (resulting in an `EXDEV` error), but this hasn't been added since the same error can happen on Unix and is already unhandled there. This change completely fixes the `dedup.t` test on Windows. This change also seems to address excessive cache duplication encountered on windows (see #13713). --------- Signed-off-by: Roven Lamar Gabriel <nevor@nevor.net>

otherlibs/stdune/src/fpath.ml

Signed-off-by: Nicolás Ojeda Bär <n.oje.bar@gmail.com>

…plication_rename_on_windows

Signed-off-by: Roven Lamar Gabriel <nevor@nevor.net>

nojb · 2026-03-02T20:46:34Z

CI failure is unrelated. Merging!

The `Io.portable_hardlink` function was systematically copying files on Windows instead of trying to create hard links. Hard links have been available for a while on NTFS and have also been available for ReFS for a coupe of years. This availability is not tied to developer mode capabilities (unlike symlinks), which means we can generally expect a Windows environment to be able to create hard links. This PR removes the systematic copy and adds the `EINVAL` error as a fallback signal in case Dune tries to create a hard link on a filesystem that does not support it. The later reduces the risk of a breaking change. Note that a copy fallback could be used when a cross-filesystem link is attempted (resulting in an `EXDEV` error), but this hasn't been added since the same error can happen on Unix and is already unhandled there. This change completely fixes the `dedup.t` test on Windows. This change also seems to address excessive cache duplication encountered on windows (see ocaml#13713). --------- Signed-off-by: Roven Lamar Gabriel <nevor@nevor.net>

…deduplicating Dune cache (ocaml#13713) In the Dune cache, when a temp artifact already exists in the cache, Dune attempts deduplication by deleting the temp artifact, linking it to the file already in the cache, and then moving the temp artifact to the build directory. The last step fails on Windows because Dune sets a read-only attribute on the destination file, causing `Unix.rename` to fail with `EACCES` in this case. Since the operation fails, Dune does not consider the file cached. Combined with the fact that this seems to happen quite often [1] on Windows, this effectively nullifies the cache speedup. This PR creates a helper function that removes the read-only attribute on the destination file before trying to overwrite it (similar to the existing `win32_unlink`) and use it in the deduplication logic of the cache, fixing the issue. _Note: This issue does not exist on Unix. This discrepancy is also being addressed directly on OCaml's side: ocaml/ocaml#14602 The test dedup.t already exhibits the issue on Windows. The `dune_cmd stat hardlinks _build/default/target` command returns 1 instead of the expected 3. This PR bumps the result to 2. To make the test completely pass, another issue around `Io.portable_hardlink` on Windows still needs to be addressed [1]. [1] It seems that the fact that on windows dune always copies files instead of trying to create a hardlink is linked to the fact that this deduplication happen more often on windows. See ocaml#13714. --------- Signed-off-by: Roven Lamar Gabriel <nevor@nevor.net>

@Alizter

CHANGES: ### Fixed - `Dyn.to_string` now uses a smarter way to convert floats. This ensures that floats are printed with enough precision to round-trip and are valid OCaml lexemes. (ocaml/dune#12982, fixes ocaml/dune#12980, @Alizter) - Fix `dune install --prefix` failing with relative paths outside the workspace like `../foo` (ocaml/dune#12993, fixes ocaml/dune#12241, @benodiwal) - Place the default trace file inside the build directory at the workspace root, rather than relative to the current directory. (ocaml/dune#13735, @vouillon) - Fixed interpreting relative paths in `%{bin:..}` and `%{bin-available:..}`. These are now interpreted correctly, relative to the dune file they're in. (ocaml/dune#13712, fixes ocaml/dune#9564, @anmonteiro) - Delete sandboxes with broken permissions (ocaml/dune#13511, @rgrinberg) - Fix compiling Menhir parsers that refer to sibling modules within a subdirectory of `(include_subdirs qualified)`. (ocaml/dune#13118, fixes ocaml/dune#11119, @anmonteiro) - Fixed the dependency specification of C stubs, which could result in C stubs not getting rebuilt when needed (which could in turn lead to segmentation faults and other hard-to-track bugs). (ocaml/dune#13652, fixes ocaml/dune#13651, @nojb) - Fix the Dune cache on Windows by correctly handling renames onto read-only files. Before this change, the Dune cache would be filled but the stored artifacts would not generally be usable by Dune. (ocaml/dune#13713, @Nevor) - Fix rpc not transferring promotion warnings to the client (ocaml/dune#12604, fixes ocaml/dune#12578, @ElectreAAS) - Fix issue where `dune exec -w` was unable to kill running programs on rebuild. (ocaml/dune#12360, fixes ocaml/dune#12323, @Alizter) - Fix package extraction on systems with tar implementations that don't auto-detect compression (e.g., OpenBSD). Dune now passes explicit decompression flags (-z for gzip, -j for bzip2) when needed, and provides clear error messages for unsupported formats like XZ and LZMA. (ocaml/dune#13688, fixes ocaml/dune#10123, @Alizter) - Resolve context and workspace binaries introduced by the respective `(env (binaries ..))` stanzas. (ocaml/dune#12952, fixes ocaml/dune#6220, @anmonteiro) - Fix `diff` promotions originating from sandboxed rules. Previously, they would be completely ignored as the sandbox with the promoted file would be destroyed if the promotion fired (ocaml/dune#13520, @rgrinberg) - Fix failure to digest installed directory targets, allowing them to be used as dependencies to other rules. (ocaml/dune#13045, @anmonteiro) - Fix handling of `(select ..)` field when used with `(include_subdirs ..)`. `(select <path> from ..)` modules now parse `path` as a relative path starting from the module group root (ocaml/dune#13175, fixes ocaml/dune#4383, ocaml/dune#12450, @anmonteiro) - Fix dune trying to kill processes that were already reaped due to race conditions (ocaml/dune#13245, @rgrinberg) - Add `O_CLOEXEC` to all files used for stdin/stdout/stderr (ocaml/dune#13385, @rgrinberg) - Fix `$ dune promote dir/foo` when `dir` does not exist (ocaml/dune#13493, @rgrinberg) - Fix `(select ..)` field evaluation when a transitive library has optional dependencies (fixes ocaml/dune#13299, ocaml/dune#13389, @anmonteiro) - Fix sandboxed builds of `library` stanzas that set `(stdlib (modules_before_stdlib ..))` (ocaml/dune#13624, @anmonteiro) - Dune cache: use of hard links under Windows. (ocaml/dune#13714, @Nevor) - Fixed non-build caches not following `$DUNE_CACHE_ROOT` and instead only relying on `$XDG_CACHE_HOME`. This means the normal build cache moves: `$DUNE_CACHE_ROOT -> $DUNE_CACHE_ROOT/db` (no changes if that variable was unset). Affected users can prevent a full cache invalidation by moving previous contents: `cd $DUNE_CACHE_ROOT; mkdir db; mv <contents of directory> db`. (ocaml/dune#11612, fixes ocaml/dune#11584, @ElectreAAS) - `$ dune promotion list` writes output to stdout rather than stderr (ocaml/dune#13462) - Improve handling of empty files in the `diff` action. These are now correctly distinguished from *empty* files. (ocaml/dune#13696, @rgrinberg) - Pass `/dev/null` to `--diff-command` instead of non-existent files (ocaml/dune#13696, @rgrinberg) - Fix failure when multiple `rocq.extraction` stanzas existing in a directory (ocaml/dune#13531, fixes ocaml/dune#8042, @rlepigre-skylabs-ai) - Print `$ dune promotion show` output to stdout rather than stderr (ocaml/dune#13481, @rgrinberg) - Fix deadlock in the `memo` library in the presence of dependency cycles (ocaml/dune#13625, @anmonteiro) - Fix promotions that modify a directory into a file (ocaml/dune#13516, fixes ocaml/dune#4067, @rgrinberg) - Fix installation of implementations of virtual libraries. This failed when the implementation had no private modules, but the virtual library did (ocaml/dune#10635, @rgrinberg) - Respect the `(dir ..)` field on packages when setting up cram tests (ocaml/dune#13581, @rgrinberg) ### Added - Add support for generating `.cms` files using oxcaml and adding `.cms` or `.cmt` files as compilation dependencies (ocaml/dune#13397, @spiessimon) - Add trace events for custom actions (ocaml/dune#13265, @rgrinberg) - Allow enabling extensions with `(using ..)` in `dune-workspace` files (ocaml/dune#13395, @spiessimon) - Add sandbox extraction trace event (ocaml/dune#13544, @rgrinberg) - Add the initial cwd to the first config event (ocaml/dune#13026, @rgrinberg) - Dune dune produces trace events in `DUNE_ACTION_TRACE_DIR` if this variable is set. (ocaml/dune#13302, @rgrinberg) - Add file watching events to the trace file (ocaml/dune#13038, @rgrinberg) - Introduce the `$ dune trace cat` subcommand to view the trace file. (ocaml/dune#13055, @rgrinberg) - Add diagnostic events to the trace. (ocaml/dune#13041, @rgrinberg) - Add `DUNE_JOBS` environment variable for controlling concurrency of Dune from environment. The `INSIDE_DUNE` variable also now no longer controls concurrency (ocaml/dune#12800, @Alizter) - Support for Rocq expected output tests (ocaml/dune#13632, @rlepigre-skylabs-ai) - Add `rusage` information to completed processes in the trace (@rgrinberg, ocaml/dune#13241) - Add process start events to the trace (ocaml/dune#13261, rgrinberg) - Generate odoc documentation in markdown using the `@doc-markdown` alias (ocaml/dune#12581, @davesnx) - Add timing information for every command executed by cram (ocaml/dune#13092, @rgrinberg) - Add the workspace root to the config trace event (ocaml/dune#12922, @rgrinberg) - Introduce the `dune-action-trace` library. This public library is to be used by custom actions to emit trace events while executed as part of a dune build. The trace events emitted through this library will be incorporated into dune's own trace (ocaml/dune#13348, @rgrinberg) - Add `dune-find-dominating` to `dune.el`, a command to find the dominating dune file. (ocaml/dune#12696, @arvidj) - Add a `--no-recursive` flag to `$ dune describe workspace` (ocaml/dune#13590, @rgrinberg) - Trace events for files written directly by dune (ocaml/dune#13618, @rgrinberg) - Allow expansion of special forms like `(:include ..)` and `%{read-lines:..}` in the `modules` specification for the `ocamllex`, `ocamlyacc` and `menhir` stanzas. (ocaml/dune#13105, ocaml/dune#13135, ocaml/dune#13157, @anmonteiro) - Add a trace event for snapshotting the asndbox (ocaml/dune#13541, @rgrinberg) - Add signal send and receive events to the trace (ocaml/dune#13193, @rgrinberg) - Emit final trace event before exiting. (ocaml/dune#13018, @rgrinberg) - `dune runtest` can now run individual test executables from `(tests)` stanzas and inline tests from `(library (inline_tests))` stanzas by providing their source files as arguments. (ocaml/dune#13064, fixes ocaml/dune#870, @Alizter) - Add a `shell` field to the cram stanza. This field allows customizing the shell to be `bash` rather than `sh` (ocaml/dune#13083, @haochenx) ### Changed - Start sandboxing the execution of tests defined with the `test` and `tests` stanzas (ocaml/dune#13510, ocaml/dune#13617, @rgrinberg) - Disabled cram tests can now be run explicitly with `dune runtest disabled.t`. The `enabled_if` field now only controls whether a test is included in the `@runtest` alias. (ocaml/dune#13081, @Alizter) - Process categories in trace events are moved to their own field in `args` (ocaml/dune#13024, @rgrinberg) - Sandbox running `ocamllex` and `ocamlyacc` actions. (ocaml/dune#13098, @anmonteiro) - Sandboxing mdx test actions is now the default starting from `0.5` (ocaml/dune#13504, @rgrinberg) - Start sandboxing Melange rules by default in the `(library ..)` and `(melange.emit ..)` stanzas (ocaml/dune#13619, @anmonteiro) - Introduce a promotion trace event and remove the corresponding verbose log message. (ocaml/dune#12949, ocaml/dune#13444, @rgrinberg) - Change dune's trace format to emit canonical s-expressions. This improves performance and is better aligned with dune's usage of the format elsewhere. `$ dune trace cat` can also emit the trace in `--chrome-trace` for perfetto, or `--sexp` for regular s-expressions for interactive usage. (ocaml/dune#13059, @rgrinberg) - Move all logging statements to the trace file. All log statements now contain structured payloads (ocaml/dune#13015, fixes ocaml/dune#12904, @rgrinberg) - Add a target resolution event to replace the equivalent log message (ocaml/dune#12955, @rgrinberg)

@Alizter

CHANGES: ### Fixed - `Dyn.to_string` now uses a smarter way to convert floats. This ensures that floats are printed with enough precision to round-trip and are valid OCaml lexemes. (ocaml/dune#12982, fixes ocaml/dune#12980, @Alizter) - Fix `dune install --prefix` failing with relative paths outside the workspace like `../foo` (ocaml/dune#12993, fixes ocaml/dune#12241, @benodiwal) - Place the default trace file inside the build directory at the workspace root, rather than relative to the current directory. (ocaml/dune#13735, @vouillon) - Fixed interpreting relative paths in `%{bin:..}` and `%{bin-available:..}`. These are now interpreted correctly, relative to the dune file they're in. (ocaml/dune#13712, fixes ocaml/dune#9564, @anmonteiro) - Delete sandboxes with broken permissions (ocaml/dune#13511, @rgrinberg) - Fix compiling Menhir parsers that refer to sibling modules within a subdirectory of `(include_subdirs qualified)`. (ocaml/dune#13118, fixes ocaml/dune#11119, @anmonteiro) - Fixed the dependency specification of C stubs, which could result in C stubs not getting rebuilt when needed (which could in turn lead to segmentation faults and other hard-to-track bugs). (ocaml/dune#13652, fixes ocaml/dune#13651, @nojb) - Fix the Dune cache on Windows by correctly handling renames onto read-only files. Before this change, the Dune cache would be filled but the stored artifacts would not generally be usable by Dune. (ocaml/dune#13713, @Nevor) - Fix rpc not transferring promotion warnings to the client (ocaml/dune#12604, fixes ocaml/dune#12578, @ElectreAAS) - Fix issue where `dune exec -w` was unable to kill running programs on rebuild. (ocaml/dune#12360, fixes ocaml/dune#12323, @Alizter) - Fix package extraction on systems with tar implementations that don't auto-detect compression (e.g., OpenBSD). Dune now passes explicit decompression flags (-z for gzip, -j for bzip2) when needed, and provides clear error messages for unsupported formats like XZ and LZMA. (ocaml/dune#13688, fixes ocaml/dune#10123, @Alizter) - Resolve context and workspace binaries introduced by the respective `(env (binaries ..))` stanzas. (ocaml/dune#12952, fixes ocaml/dune#6220, @anmonteiro) - Fix `diff` promotions originating from sandboxed rules. Previously, they would be completely ignored as the sandbox with the promoted file would be destroyed if the promotion fired (ocaml/dune#13520, @rgrinberg) - Fix failure to digest installed directory targets, allowing them to be used as dependencies to other rules. (ocaml/dune#13045, @anmonteiro) - Fix handling of `(select ..)` field when used with `(include_subdirs ..)`. `(select <path> from ..)` modules now parse `path` as a relative path starting from the module group root (ocaml/dune#13175, fixes ocaml/dune#4383, ocaml/dune#12450, @anmonteiro) - Fix dune trying to kill processes that were already reaped due to race conditions (ocaml/dune#13245, @rgrinberg) - Add `O_CLOEXEC` to all files used for stdin/stdout/stderr (ocaml/dune#13385, @rgrinberg) - Fix `$ dune promote dir/foo` when `dir` does not exist (ocaml/dune#13493, @rgrinberg) - Fix `(select ..)` field evaluation when a transitive library has optional dependencies (fixes ocaml/dune#13299, ocaml/dune#13389, @anmonteiro) - Fix sandboxed builds of `library` stanzas that set `(stdlib (modules_before_stdlib ..))` (ocaml/dune#13624, @anmonteiro) - Dune cache: use of hard links under Windows. (ocaml/dune#13714, @Nevor) - Fixed non-build caches not following `$DUNE_CACHE_ROOT` and instead only relying on `$XDG_CACHE_HOME`. This means the normal build cache moves: `$DUNE_CACHE_ROOT -> $DUNE_CACHE_ROOT/db` (no changes if that variable was unset). Affected users can prevent a full cache invalidation by moving previous contents: `cd $DUNE_CACHE_ROOT; mkdir db; mv <contents of directory> db`. (ocaml/dune#11612, fixes ocaml/dune#11584, @ElectreAAS) - `$ dune promotion list` writes output to stdout rather than stderr (ocaml/dune#13462) - Improve handling of empty files in the `diff` action. These are now correctly distinguished from *empty* files. (ocaml/dune#13696, @rgrinberg) - Pass `/dev/null` to `--diff-command` instead of non-existent files (ocaml/dune#13696, @rgrinberg) - Fix failure when multiple `rocq.extraction` stanzas existing in a directory (ocaml/dune#13531, fixes ocaml/dune#8042, @rlepigre-skylabs-ai) - Print `$ dune promotion show` output to stdout rather than stderr (ocaml/dune#13481, @rgrinberg) - Fix deadlock in the `memo` library in the presence of dependency cycles (ocaml/dune#13625, @anmonteiro) - Fix promotions that modify a directory into a file (ocaml/dune#13516, fixes ocaml/dune#4067, @rgrinberg) - Fix installation of implementations of virtual libraries. This failed when the implementation had no private modules, but the virtual library did (ocaml/dune#10635, @rgrinberg) - Respect the `(dir ..)` field on packages when setting up cram tests (ocaml/dune#13581, @rgrinberg) ### Added - Add support for generating `.cms` files using oxcaml and adding `.cms` or `.cmt` files as compilation dependencies (ocaml/dune#13397, @spiessimon) - Add trace events for custom actions (ocaml/dune#13265, @rgrinberg) - Allow enabling extensions with `(using ..)` in `dune-workspace` files (ocaml/dune#13395, @spiessimon) - Add sandbox extraction trace event (ocaml/dune#13544, @rgrinberg) - Add the initial cwd to the first config event (ocaml/dune#13026, @rgrinberg) - Dune dune produces trace events in `DUNE_ACTION_TRACE_DIR` if this variable is set. (ocaml/dune#13302, @rgrinberg) - Add file watching events to the trace file (ocaml/dune#13038, @rgrinberg) - Introduce the `$ dune trace cat` subcommand to view the trace file. (ocaml/dune#13055, @rgrinberg) - Add diagnostic events to the trace. (ocaml/dune#13041, @rgrinberg) - Add `DUNE_JOBS` environment variable for controlling concurrency of Dune from environment. The `INSIDE_DUNE` variable also now no longer controls concurrency (ocaml/dune#12800, @Alizter) - Support for Rocq expected output tests (ocaml/dune#13632, @rlepigre-skylabs-ai) - Add `rusage` information to completed processes in the trace (@rgrinberg, ocaml/dune#13241) - Add process start events to the trace (ocaml/dune#13261, rgrinberg) - Generate odoc documentation in markdown using the `@doc-markdown` alias (ocaml/dune#12581, @davesnx) - Add timing information for every command executed by cram (ocaml/dune#13092, @rgrinberg) - Add the workspace root to the config trace event (ocaml/dune#12922, @rgrinberg) - Introduce the `dune-action-trace` library. This public library is to be used by custom actions to emit trace events while executed as part of a dune build. The trace events emitted through this library will be incorporated into dune's own trace (ocaml/dune#13348, @rgrinberg) - Add `dune-find-dominating` to `dune.el`, a command to find the dominating dune file. (ocaml/dune#12696, @arvidj) - Add a `--no-recursive` flag to `$ dune describe workspace` (ocaml/dune#13590, @rgrinberg) - Trace events for files written directly by dune (ocaml/dune#13618, @rgrinberg) - Allow expansion of special forms like `(:include ..)` and `%{read-lines:..}` in the `modules` specification for the `ocamllex`, `ocamlyacc` and `menhir` stanzas. (ocaml/dune#13105, ocaml/dune#13135, ocaml/dune#13157, @anmonteiro) - Add a trace event for snapshotting the asndbox (ocaml/dune#13541, @rgrinberg) - Add signal send and receive events to the trace (ocaml/dune#13193, @rgrinberg) - Emit final trace event before exiting. (ocaml/dune#13018, @rgrinberg) - `dune runtest` can now run individual test executables from `(tests)` stanzas and inline tests from `(library (inline_tests))` stanzas by providing their source files as arguments. (ocaml/dune#13064, fixes ocaml/dune#870, @Alizter) - Add a `shell` field to the cram stanza. This field allows customizing the shell to be `bash` rather than `sh` (ocaml/dune#13083, @haochenx) ### Changed - Start sandboxing the execution of tests defined with the `test` and `tests` stanzas (ocaml/dune#13510, ocaml/dune#13617, @rgrinberg) - Disabled cram tests can now be run explicitly with `dune runtest disabled.t`. The `enabled_if` field now only controls whether a test is included in the `@runtest` alias. (ocaml/dune#13081, @Alizter) - Process categories in trace events are moved to their own field in `args` (ocaml/dune#13024, @rgrinberg) - Sandbox running `ocamllex` and `ocamlyacc` actions. (ocaml/dune#13098, @anmonteiro) - Sandboxing mdx test actions is now the default starting from `0.5` (ocaml/dune#13504, @rgrinberg) - Start sandboxing Melange rules by default in the `(library ..)` and `(melange.emit ..)` stanzas (ocaml/dune#13619, @anmonteiro) - Introduce a promotion trace event and remove the corresponding verbose log message. (ocaml/dune#12949, ocaml/dune#13444, @rgrinberg) - Change dune's trace format to emit canonical s-expressions. This improves performance and is better aligned with dune's usage of the format elsewhere. `$ dune trace cat` can also emit the trace in `--chrome-trace` for perfetto, or `--sexp` for regular s-expressions for interactive usage. (ocaml/dune#13059, @rgrinberg) - Move all logging statements to the trace file. All log statements now contain structured payloads (ocaml/dune#13015, fixes ocaml/dune#12904, @rgrinberg) - Add a target resolution event to replace the equivalent log message (ocaml/dune#12955, @rgrinberg)

@Alizter

CHANGES: ### Fixed - `Dyn.to_string` now uses a smarter way to convert floats. This ensures that floats are printed with enough precision to round-trip and are valid OCaml lexemes. (ocaml/dune#12982, fixes ocaml/dune#12980, @Alizter) - Fix `dune install --prefix` failing with relative paths outside the workspace like `../foo` (ocaml/dune#12993, fixes ocaml/dune#12241, @benodiwal) - Place the default trace file inside the build directory at the workspace root, rather than relative to the current directory. (ocaml/dune#13735, @vouillon) - Fixed interpreting relative paths in `%{bin:..}` and `%{bin-available:..}`. These are now interpreted correctly, relative to the dune file they're in. (ocaml/dune#13712, fixes ocaml/dune#9564, @anmonteiro) - Delete sandboxes with broken permissions (ocaml/dune#13511, @rgrinberg) - Fix compiling Menhir parsers that refer to sibling modules within a subdirectory of `(include_subdirs qualified)`. (ocaml/dune#13118, fixes ocaml/dune#11119, @anmonteiro) - Fixed the dependency specification of C stubs, which could result in C stubs not getting rebuilt when needed (which could in turn lead to segmentation faults and other hard-to-track bugs). (ocaml/dune#13652, fixes ocaml/dune#13651, @nojb) - Fix the Dune cache on Windows by correctly handling renames onto read-only files. Before this change, the Dune cache would be filled but the stored artifacts would not generally be usable by Dune. (ocaml/dune#13713, @Nevor) - Fix rpc not transferring promotion warnings to the client (ocaml/dune#12604, fixes ocaml/dune#12578, @ElectreAAS) - Fix issue where `dune exec -w` was unable to kill running programs on rebuild. (ocaml/dune#12360, fixes ocaml/dune#12323, @Alizter) - Resolve context and workspace binaries introduced by the respective `(env (binaries ..))` stanzas. (ocaml/dune#12952, fixes ocaml/dune#6220, @anmonteiro) - Fix `diff` promotions originating from sandboxed rules. Previously, they would be completely ignored as the sandbox with the promoted file would be destroyed if the promotion fired (ocaml/dune#13520, @rgrinberg) - Fix failure to digest installed directory targets, allowing them to be used as dependencies to other rules. (ocaml/dune#13045, @anmonteiro) - Fix handling of `(select ..)` field when used with `(include_subdirs ..)`. `(select <path> from ..)` modules now parse `path` as a relative path starting from the module group root (ocaml/dune#13175, fixes ocaml/dune#4383, ocaml/dune#12450, @anmonteiro) - Fix dune trying to kill processes that were already reaped due to race conditions (ocaml/dune#13245, @rgrinberg) - Add `O_CLOEXEC` to all files used for stdin/stdout/stderr (ocaml/dune#13385, @rgrinberg) - Fix `$ dune promote dir/foo` when `dir` does not exist (ocaml/dune#13493, @rgrinberg) - Fix `(select ..)` field evaluation when a transitive library has optional dependencies (fixes ocaml/dune#13299, ocaml/dune#13389, @anmonteiro) - Fix sandboxed builds of `library` stanzas that set `(stdlib (modules_before_stdlib ..))` (ocaml/dune#13624, @anmonteiro) - Dune cache: use of hard links under Windows. (ocaml/dune#13714, @Nevor) - Fixed non-build caches not following `$DUNE_CACHE_ROOT` and instead only relying on `$XDG_CACHE_HOME`. This means the normal build cache moves: `$DUNE_CACHE_ROOT -> $DUNE_CACHE_ROOT/db` (no changes if that variable was unset). Affected users can prevent a full cache invalidation by moving previous contents: `cd $DUNE_CACHE_ROOT; mkdir db; mv <contents of directory> db`. (ocaml/dune#11612, fixes ocaml/dune#11584, @ElectreAAS) - `$ dune promotion list` writes output to stdout rather than stderr (ocaml/dune#13462) - Improve handling of empty files in the `diff` action. These are now correctly distinguished from *empty* files. (ocaml/dune#13696, @rgrinberg) - Pass `/dev/null` to `--diff-command` instead of non-existent files (ocaml/dune#13696, @rgrinberg) - Fix failure when multiple `rocq.extraction` stanzas existing in a directory (ocaml/dune#13531, fixes ocaml/dune#8042, @rlepigre-skylabs-ai) - Print `$ dune promotion show` output to stdout rather than stderr (ocaml/dune#13481, @rgrinberg) - Fix deadlock in the `memo` library in the presence of dependency cycles (ocaml/dune#13625, @anmonteiro) - Fix promotions that modify a directory into a file (ocaml/dune#13516, fixes ocaml/dune#4067, @rgrinberg) - Fix installation of implementations of virtual libraries. This failed when the implementation had no private modules, but the virtual library did (ocaml/dune#10635, @rgrinberg) - Respect the `(dir ..)` field on packages when setting up cram tests (ocaml/dune#13581, @rgrinberg) ### Added - Add support for generating `.cms` files using oxcaml and adding `.cms` or `.cmt` files as compilation dependencies (ocaml/dune#13397, @spiessimon) - Add trace events for custom actions (ocaml/dune#13265, @rgrinberg) - Allow enabling extensions with `(using ..)` in `dune-workspace` files (ocaml/dune#13395, @spiessimon) - Add sandbox extraction trace event (ocaml/dune#13544, @rgrinberg) - Add the initial cwd to the first config event (ocaml/dune#13026, @rgrinberg) - Dune dune produces trace events in `DUNE_ACTION_TRACE_DIR` if this variable is set. (ocaml/dune#13302, @rgrinberg) - Add file watching events to the trace file (ocaml/dune#13038, @rgrinberg) - Introduce the `$ dune trace cat` subcommand to view the trace file. (ocaml/dune#13055, @rgrinberg) - Add diagnostic events to the trace. (ocaml/dune#13041, @rgrinberg) - Add `DUNE_JOBS` environment variable for controlling concurrency of Dune from environment. The `INSIDE_DUNE` variable also now no longer controls concurrency (ocaml/dune#12800, @Alizter) - Support for Rocq expected output tests (ocaml/dune#13632, @rlepigre-skylabs-ai) - Add `rusage` information to completed processes in the trace (@rgrinberg, ocaml/dune#13241) - Add process start events to the trace (ocaml/dune#13261, rgrinberg) - Generate odoc documentation in markdown using the `@doc-markdown` alias (ocaml/dune#12581, @davesnx) - Add timing information for every command executed by cram (ocaml/dune#13092, @rgrinberg) - Add the workspace root to the config trace event (ocaml/dune#12922, @rgrinberg) - Introduce the `dune-action-trace` library. This public library is to be used by custom actions to emit trace events while executed as part of a dune build. The trace events emitted through this library will be incorporated into dune's own trace (ocaml/dune#13348, @rgrinberg) - Add `dune-find-dominating` to `dune.el`, a command to find the dominating dune file. (ocaml/dune#12696, @arvidj) - Add a `--no-recursive` flag to `$ dune describe workspace` (ocaml/dune#13590, @rgrinberg) - Trace events for files written directly by dune (ocaml/dune#13618, @rgrinberg) - Allow expansion of special forms like `(:include ..)` and `%{read-lines:..}` in the `modules` specification for the `ocamllex`, `ocamlyacc` and `menhir` stanzas. (ocaml/dune#13105, ocaml/dune#13135, ocaml/dune#13157, @anmonteiro) - Add a trace event for snapshotting the asndbox (ocaml/dune#13541, @rgrinberg) - Add signal send and receive events to the trace (ocaml/dune#13193, @rgrinberg) - Emit final trace event before exiting. (ocaml/dune#13018, @rgrinberg) - `dune runtest` can now run individual test executables from `(tests)` stanzas and inline tests from `(library (inline_tests))` stanzas by providing their source files as arguments. (ocaml/dune#13064, fixes ocaml/dune#870, @Alizter) - Add a `shell` field to the cram stanza. This field allows customizing the shell to be `bash` rather than `sh` (ocaml/dune#13083, @haochenx) ### Changed - Start sandboxing the execution of tests defined with the `test` and `tests` stanzas (ocaml/dune#13510, ocaml/dune#13617, @rgrinberg) - Disabled cram tests can now be run explicitly with `dune runtest disabled.t`. The `enabled_if` field now only controls whether a test is included in the `@runtest` alias. (ocaml/dune#13081, @Alizter) - Process categories in trace events are moved to their own field in `args` (ocaml/dune#13024, @rgrinberg) - Sandbox running `ocamllex` and `ocamlyacc` actions. (ocaml/dune#13098, @anmonteiro) - Sandboxing mdx test actions is now the default starting from `0.5` (ocaml/dune#13504, @rgrinberg) - Start sandboxing Melange rules by default in the `(library ..)` and `(melange.emit ..)` stanzas (ocaml/dune#13619, @anmonteiro) - Introduce a promotion trace event and remove the corresponding verbose log message. (ocaml/dune#12949, ocaml/dune#13444, @rgrinberg) - Change dune's trace format to emit canonical s-expressions. This improves performance and is better aligned with dune's usage of the format elsewhere. `$ dune trace cat` can also emit the trace in `--chrome-trace` for perfetto, or `--sexp` for regular s-expressions for interactive usage. (ocaml/dune#13059, @rgrinberg) - Move all logging statements to the trace file. All log statements now contain structured payloads (ocaml/dune#13015, fixes ocaml/dune#12904, @rgrinberg) - Add a target resolution event to replace the equivalent log message (ocaml/dune#12955, @rgrinberg)

Nevor mentioned this pull request Mar 2, 2026

Dune cache: use hard links on Windows #13714

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rgrinberg requested a review from nojb March 2, 2026 14:01

Nevor force-pushed the fix_dune_cache_deduplication_rename_on_windows branch from 39f0925 to 8c334c1 Compare March 2, 2026 14:06

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Nevor added 2 commits March 2, 2026 14:44

Add change file.

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Signed-off-by: Roven Lamar Gabriel <nevor@nevor.net>

Rephrase changes entry as suggested by @nojb.

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Signed-off-by: Roven Lamar Gabriel <nevor@nevor.net>

Nevor force-pushed the fix_dune_cache_deduplication_rename_on_windows branch from b913ccc to 6361b99 Compare March 2, 2026 14:46

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Update otherlibs/stdune/src/fpath.ml

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Co-authored-by: Ali Caglayan <alizter@gmail.com> Signed-off-by: Roven Lamar Gabriel <nevor@nevor.net>

Nevor force-pushed the fix_dune_cache_deduplication_rename_on_windows branch from 91ddbb4 to 6d36ba6 Compare March 2, 2026 18:47

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nojb and others added 2 commits March 2, 2026 19:56

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Signed-off-by: Nicolás Ojeda Bär <n.oje.bar@gmail.com>

Merge remote-tracking branch 'upstream/main' into fix_dune_cache_dedu…

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Expand on both arguments.

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nojb force-pushed the fix_dune_cache_deduplication_rename_on_windows branch from e1a7b91 to b7aee6d Compare March 2, 2026 20:16

nojb mentioned this pull request Mar 2, 2026

{Sys,Unix}.rename: on Windows, allow renaming onto read-only file ocaml/ocaml#14602

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nojb merged commit cc1a16c into ocaml:main Mar 2, 2026
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shonfeder mentioned this pull request Mar 11, 2026

[new release] dune (18 packages) (3.22.0~alpha1) ocaml/opam-repository#29535

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[new release] dune (18 packages) (3.22.0~alpha2) ocaml/opam-repository#29547

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[new release] dune (18 packages) (3.22.0) ocaml/opam-repository#29562

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fix: allow rename to overwrite read-only destination on Windows when deduplicating Dune cache#13713

fix: allow rename to overwrite read-only destination on Windows when deduplicating Dune cache#13713
nojb merged 7 commits intoocaml:mainfrom
Nevor:fix_dune_cache_deduplication_rename_on_windows

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Nevor commented Mar 2, 2026 •

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