libstore-c: add nix_store_get_fs_closure #14025

RossComputerGuy · 2025-09-19T17:33:11Z

Motivation

Adds a way to call the store API's computeFSClosure function from C.

Context

I'd like to be able to call this from the nixops4 Rust bindings.

Upstreams DeterminateSystems#209

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src/libstore-c/nix_api_store.cc

src/libstore-c/nix_api_store.h

Ericson2314 · 2025-09-19T21:13:10Z

src/libstore-c/nix_api_store.h

+ * @param[out] context Optional, stores error information
+ * @param[in] store nix store reference
+ * @param[in] store_path The path to compute from
+ * @param[in] flip_direction


@roberth is the right thing to just copy the doc from the C++ function?

If the docs are good, then that's fine

Ericson2314 · 2025-09-19T21:14:47Z

src/libstore-c/nix_api_store.h

+ * @param[in] callback The function to call for every store path
+ * @param[in] userdata The userdata to pass to the callback
+ */
+nix_err nix_store_get_fs_closure(


I think it would be better to put this above nix_store_realise

Ericson2314 · 2025-09-19T21:15:30Z

I assigned to @roberth as he is defacto code owner of this.

roberth · 2025-09-19T21:45:42Z

src/libstore-c/nix_api_store.h

+ * @param[in] flip_direction
+ * @param[in] include_outputs
+ * @param[in] include_derivers
+ * @param[in] callback The function to call for every store path


Let's afford the impl some more freedom

Suggested change

* @param[in] callback The function to call for every store path

* @param[in] callback The function to call for every store path, in no particular order

Ericson2314 · 2025-09-19T22:07:06Z

Oh and actually I would like to not expose flip direction, as many stores don't support the reverse direction.

(I had an old blocked store API PR fo this, it would be nice to not repeat the same IMO mistake in the C API.)

RossComputerGuy · 2025-09-19T22:28:09Z

Oh and actually I would like to not expose flip direction, as many stores don't support the reverse direction.

Should the C++ API reflect that? Imo, I prefer having feature parity to the C++ API as close as C can get.

roberth · 2025-09-19T22:58:25Z

Is it feasible to create a small store path graph using the store operations at this point?
Ideally we could test this without getting the evaluator involved, but otherwise, we could have a test in libexpr-tests instead, where we can do instantiations and realisations, no problem.

RossComputerGuy · 2025-09-22T19:38:00Z

Is it feasible to create a small store path graph using the store operations at this point?

I think we're close to making that possible, I'm not sure what else is needed but I think it may be possible.

roberth

Error propagation is trickier than necessary without early abort
A test would be important for the operational stability of this feature

roberth · 2025-10-06T10:24:33Z

src/libstore-c/nix_api_store.cc

+    bool include_outputs,
+    bool include_derivers,
+    void * userdata,
+    void (*callback)(void * userdata, const StorePath * store_path))


Suggested change

void (*callback)(void * userdata, const StorePath * store_path))

void (*callback)(nix_c_context * context, void * userdata, const StorePath * store_path))

roberth · 2025-10-06T10:25:15Z

src/libstore-c/nix_api_store.cc

+        if (callback) {
+            for (const auto & path : set) {
+                const StorePath tmp{path};
+                callback(userdata, &tmp);


Early abort if the callback sets an error

roberth · 2025-10-15T11:31:46Z

Oh and actually I would like to not expose flip direction, as many stores don't support the reverse direction.

We can just error in those cases. Just because something isn't universal doesn't mean we shouldn't support it at all.
I don't think anyone has any ambition to restructure the internal closure computations; seems quite uninteresting at this point, so I don't think this parameter will hold anyone back either in their refactors.
It's not like we'd get rid of the functionality anyway. The CLI needs it, for one.

roberth · 2025-10-15T11:32:28Z

LGTM with added tests in #14254.
Merging that will merge this :)

RossComputerGuy requested a review from edolstra as a code owner September 19, 2025 17:33

github-actions bot added the c api Nix as a C library with a stable interface label Sep 19, 2025

Ericson2314 reviewed Sep 19, 2025

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Ericson2314 reviewed Sep 19, 2025

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RossComputerGuy force-pushed the upstream-RossComputerGuy/feat/expose-computefsclosure branch 2 times, most recently from 3267618 to 9237e52 Compare September 19, 2025 17:57

RossComputerGuy mentioned this pull request Sep 19, 2025

feat: nix_store::store add get_fs_closure function nixops4/nixops4#120

Closed

Ericson2314 requested a review from roberth September 19, 2025 21:11

Ericson2314 reviewed Sep 19, 2025

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RossComputerGuy force-pushed the upstream-RossComputerGuy/feat/expose-computefsclosure branch from 9237e52 to d93cd0a Compare September 19, 2025 21:30

roberth reviewed Sep 19, 2025

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RossComputerGuy force-pushed the upstream-RossComputerGuy/feat/expose-computefsclosure branch from d93cd0a to 1f8a5cc Compare September 19, 2025 21:47

roberth reviewed Oct 6, 2025

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libstore-c: add nix_store_get_fs_closure

9abcc68

RossComputerGuy force-pushed the upstream-RossComputerGuy/feat/expose-computefsclosure branch from 1f8a5cc to 9abcc68 Compare October 6, 2025 16:12

roberth mentioned this pull request Oct 15, 2025

libstore-c: add nix_store_get_fs_closure #14025 with tests and realise error fix #14254

Open

	* @param[in] callback The function to call for every store path
	* @param[in] callback The function to call for every store path, in no particular order

	void (callback)(void userdata, const StorePath * store_path))
	void (callback)(nix_c_context context, void * userdata, const StorePath * store_path))

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libstore-c: add nix_store_get_fs_closure #14025

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RossComputerGuy commented Sep 19, 2025

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Ericson2314 commented Sep 19, 2025

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Ericson2314 commented Sep 19, 2025

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RossComputerGuy commented Sep 19, 2025

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roberth commented Sep 19, 2025

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RossComputerGuy commented Sep 22, 2025

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roberth commented Oct 15, 2025

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roberth commented Oct 15, 2025

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