feat: compile_commands.json generation - #14185
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rgrinberg
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Is the alias really necessary? It's producing a single target, might as well just use that target instead of the alias. It would be fine to add this target to the check alias however. |
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I'm using an alias so that generating the target is a bit more intentional since it also promotes. Putting it in I considered introducing a configuration option, however because it is a workspace wide thing it would have to go in a config or workspace file. Having it in a dune-project file seems more natural but then that opens the question of how to compose the option which I don't know how to solve. I'm wondering if there is an easy thing we can do here. Promoting is obviously useful for clangd and ccls but I don't know if it will be something people want all the time. |
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When do you think somebody might want to build |
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It's the promoting part that's making me think here. |
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If the file isn't promoted, it's completely useless as the lsp servers will never find it. |
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@rgrinberg Should we be guarding this behind dune lang. Will that work well with workspaces? |
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I'm going to add it to |
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If you do it with the workspace, people will be able to take advantage of this feature in composed dune builds as well as packages where they haven't upgraded the dune version. On the other hand, doing it in the package is simpler for most users. |
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Generate a compilation database (compile_commands.json) for C and C++ foreign stubs. This enables language servers like clangd and ccls to provide code navigation, completion, and diagnostics for C stubs in OCaml projects. The file is generated and promoted to the workspace root when building `@check`, gated behind (lang dune 3.23). It is only produced for the merlin context and removed by dune clean. The implementation refactors foreign_rules.ml to extract shared helpers (c_compile_args, build_include_flags, compilation_flags) that are reused by both the existing C compilation rules and the new compile_commands generation. Signed-off-by: Ali Caglayan <alizter@gmail.com>
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I've rechecked locally that all is working and |
This was referenced Apr 30, 2026
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CHANGES:
### Fixed
- Auto-inject `"menhir" {>= "20180523"}` into generated opam files when the
menhir extension is used. Dune's menhir rules rely on `--infer-write-query`
and `--infer-read-reply`, which require at least this version; without the
lower bound, builds fail with older menhir installations.
(ocaml/dune#10707, @robinbb)
- Fix `--display=quiet` not suppressing "Entering directory" and "Leaving
directory" messages when using `--root`. These messages are now deferred
until there is actual output, so silent builds produce no noise.
(ocaml/dune#12974, fixes ocaml/dune#12854, @Alizter)
- Fix an internal error when a module is shared between a `rocq.theory` and
`rocq.extraction` stanza. The error now includes a hint pointing to the
conflicting stanza. (ocaml/dune#13733, @Durbatuluk1701)
- Fix cookies defined on `ppx_rewriter` being lost when that rewriter was used
as a dependency of another `ppx_rewriter`. (ocaml/dune#13737, fixes ocaml/dune#3426, @Alizter)
- Improve opam file generation for packages that set `(dir ..)`. Such packages
will now have a test target that is limited to this directory. (ocaml/dune#13778, @rgrinberg)
- Stop duplicating dune diagnostics to subscribers over RPC (ocaml/dune#13816,
@rgrinberg)
- Fix dependency cycle when using the `package` with a library
conditionally enabled via `enabled_if`. (ocaml/dune#13833, @toots)
- Fix underspecification of dependencies in the sandbox for modules with
interfaces. (ocaml/dune#13842, @anmonteiro)
- Honor sandbox settings specified inside `(:include ..)` expressions in the `deps` field
(ocaml/dune#13898, @rgrinberg)
- Fix `dune pkg lock` failing when a `pin` stanza contains a `file://` URL with
a relative path outside the workspace (ocaml/dune#13915, fixes ocaml/dune#10254, @shunueda)
- Use all stat attributes to detect patch back source tree changes (ocaml/dune#13986, @rgrinberg)
- Use device and inode number for invalidating cached digests (ocaml/dune#13991, @rgrinberg)
- Stop trying to set SO_REUSEADDR on unix sockets when setting up dune rpc
(ocaml/dune#14056, @rgrinberg)
- Fix autolocking to correctly detect changes to `(depends)` in watch mode
(ocaml/dune#14066, fixes ocaml/dune#13234, @Alizter)
- Fix incremental builds for libraries using `(wrapped (transition ...))`.
The compat shim modules were never recompiled when the inner module's
interface changed, causing "inconsistent assumptions" errors.
(ocaml/dune#14090, fixes ocaml/dune#14089, @Alizter)
- Fix Rocq configuration detection to use `rocq c --config` subcommand
instead of `rocq --config` (ocaml/dune#14093, fixes ocaml/dune#13774, @Durbatuluk1701)
- Bump dune rpc's request pending request limit 10 to 100 (ocaml/dune#14094, @rginberg)
- Invalidate stale cached digests in all build commands (ocaml/dune#14126, @rgrinberg)
- Fix `root_module` generating duplicate module definitions when a
findlib sub-package shares a directory with its parent (e.g.,
`logs.lwt` alongside `logs`). (ocaml/dune#14135, fixes ocaml/dune#6148, @robinbb)
- Fix `dune subst` prepending a duplicate `version:` field to opam
files that already contain one, instead of replacing it in place.
(ocaml/dune#14136, fixes ocaml/dune#878, @robinbb)
- Fix `@ocaml-index` alias being generated for all contexts, causing build
errors in multi-context workspaces where some libraries are disabled in
non-default contexts. The alias is now only generated for the merlin context.
(ocaml/dune#14137, fixes ocaml/dune#12007, @robinbb)
- Remove the warning about the deprecation of the coq stanza for
dune lang before 3.21 since it has been introduced in this
version (ocaml/dune#14187, @bobot)
- `$ dune init` now generates projects with correct .opam files (ocaml/dune#14192, @rgrinberg)
- Send SIGTERM before SIGKILL when cancelling child processes in watch
mode, giving cleanup handlers a chance to run before escalating.
(ocaml/dune#14224, ocaml/dune#14170, fixes ocaml/dune#2445, @robinbb)
- Correctly specify dependencies for `generate_runner` in inline tests (ocaml/dune#14276, @rgrinberg)
- Fix duplicate dune version bounds in generated opam files. When users
declare `(dune (>= X.Y))` matching or exceeding the `(lang dune X.Y)`
version, the generated opam `depends` no longer contains redundant
constraints like `{>= "2.7" & >= "2.7"}`. (ocaml/dune#3916, ocaml/dune#11106, @robinbb)
- Fix inline tests not being executed for byte-only libraries. When a library
has `(modes byte)`, the inline test runner is now linked in byte mode so the
library's test code is included. (ocaml/dune#9757, @robinbb)
### Added
- Add support for `c_library_flags` in foreign_stubs (ocaml/dune#13484, @madroach)
- Move the management of Jsoo config details out of dune (ocaml/dune#13613, @vouillon)
- Js_of_ocaml: share standalone runtimes (ocaml/dune#13621, @vouillon)
- Allow multiple `(dirs ..)` stanzas in the same Dune file. Starting with
`(lang dune 3.23)`, Dune takes the union of the specified directories
(ocaml/dune#13734, fixes ocaml/dune#6249, @anmonteiro)
- Sandboxed rules are now allowed to produce diff promotions when `(corrections
produce)` is set on the rules. Whenever such an action produces `foo.corrected`, it will
be automatically registered as a promotion for `foo` (ocaml/dune#13813, @rgrinberg)
- `$ dune clean` now accepts arguments to only remove certain targets from the
_build directory (ocaml/dune#13875, @rgrinberg)
- `$ dune promote` now promotes all paths that are a prefix of the path provided.
For example, `$ dune promote foo` will promote `foo`, `foo/bar`, `foo/bar/baz`
(but not `foobar`). (ocaml/dune#13876, @rgrinberg)
- Allow for the `diff` action to diff entire directories (ocaml/dune#13880, fixes ocaml/dune#3567, @rgrinberg)
- A hint is now emitted when trying to build a target inside a directory that
was excluded by a `(dirs ...)` stanza (ocaml/dune#13919, @mefyl).
- Add --debug-backtraces to `$ dune {promote,trace,cache}` (ocaml/dune#13933, @rgrinberg)
- Actions are now able to observe their project directory via
`DUNE_PROJECT_ROOT` (ocaml/dune#13934, @rgrinberg)
- Support hardlink sandboxing on Windows. (ocaml/dune#13987, addresses part of ocaml/dune#4362, @Alizter)
- `rocq.extraction`: Add `extracted_files` field in `(rocq 0.13)`, replacing
`extracted_modules`, supporting extraction to languages other than OCaml
(ocaml/dune#13997, @Durbatuluk1701).
- Infer source directories as dependencies when they're as reference
directories in `diff` actions.
- Add trace events for build start/stop/restarts (ocaml/dune#14163, ocaml/dune#14166, @rgrinberg)
- Generate `compile_commands.json` for C/C++ foreign stubs when building
`@check` with `(lang dune 3.23)`. This enables `clangd`, `ccls`, and other
tools that consume compilation databases. (ocaml/dune#14185, fixes ocaml/dune#3531, @Alizter)
- Add trace events for accepting clients and shutting down RPC (ocaml/dune#14232, @rgrinberg)
- Back up the default trace file as `trace.csexp.old` before each build,
preserving the previous trace for comparison. This does not apply when
`--trace-file` is used. (ocaml/dune#14269, @Alizter)
### Changed
- Dune digests target files and directories in background threads (ocaml/dune#13341,
@rgrinbreg)
- `Dyn.pp` now prints valid OCaml literals for more constructors:
- `Char` is quoted (e.g., `'a'`)
- `Int32`/`Int64`/`Nativeint` include literal suffixes (`l`/`L`/`n`)
- `Float` handles `infinity`, `neg_infinity`, and `nan`
(ocaml/dune#13394, grants ocaml/dune#13378, @Alizter)
- Bump the minimal OCaml version required to build Dune from 4.08 to 4.14.
(ocaml/dune#13533, @Alizter)
- Starting from 3.23, user rules are sandboxed by default (ocaml/dune#13805, @rgrinberg)
- Dune will no longer stat paths in the _build directory. This was done as protection
from user rules accidentally touching things in the _build directory. This is forbidden,
and dune offers rule sandboxing to prevent this (ocaml/dune#13875, @rgrinberg)
- Improve mtime precision by no longer approximating them with floats (ocaml/dune#13962,
@rgrinberg).
- Remove `--makefile` (or `-m`) in `$ dune rules`. The sexp output is the only
supported way of reflecting dune rules (ocaml/dune#14069, @rgrinberg)
- Do not automatically promote files. Now, opam files must be manually
promoted with `$ dune promote`. Their generation is triggered by `@install`,
`@runtest`, and `@opam`. In release mode, .opam files aren't generated at all
and whatever is in the source is used (ocaml/dune#14108, @rgrinberg)
- Inline test runner generation is now sandboxed (ocaml/dune#14257, @rgrinberg)
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We generate
compile_commonds.jsonand promote it to the workspace root when dune lang is 3.23. This is a compilation database containing the flags and compiler invocations for foreign stubs and archives, used by C/C++ editor support.