A different take on git submodule support for flakes #5497

kaii-zen · 2021-11-04T18:51:25Z

As the title implies, this is a whole 'nother take. Ça veut dire, it does not interact AT ALL with submodules = true;. It does involve more code though.

Idea

If a tree has a .gitmodules in it, then we:

Get the paths where submodules go
Get the respective URLs that go with those paths
Traverse the git tree to work out the revs
Construct flake-friendly URLs (git+xxxx://host/who/what?rev=xxxx etc)
Build an attrset that maps paths to flake-friendly URLs
Slap this into the attrset returned by fetchTree

That's it. It looks like this:

❯ nix eval --impure --expr 'builtins.fetchTree git+https://github.com/runtimeverification/iele-semantics' | nixfmt
{
  lastModified = 1636045922;
  lastModifiedDate = "20211104171202";
  modules = {
    "deps/secp256k1" =
      "git+https://github.com/bitcoin-core/secp256k1?allRefs=1&rev=f532bdc9f77f7bbf7e93faabfbe9c483f0a9f75f";
    plugin =
      "git+https://github.com/runtimeverification/blockchain-k-plugin?allRefs=1&rev=cc7384e565e4c8df4d17a3330cd9951d32d4830f";
    "tests/ethereum-tests" =
      "git+https://github.com/ethereum/tests.git?allRefs=1&rev=7057d0e021f7dbee37a2ddb6acf34f4946bc157d";
    "web/k-web-theme" =
      "git+https://github.com/runtimeverification/k-web-theme?allRefs=1&rev=189fe6650488f8f04dc89d25a61cdfd888cd9dd8";
  };
  narHash = "sha256-9GDWDomnRyJ47mDbygoBHThq9Q+3JGZDYTIHB8SsMlc=";
  outPath = "/nix/store/6d1w3h7fygfwl1f42x1bx6xhsrsmh7qj-source";
  rev = "431a4a44dad39aedb1dff126475cdce3b8d91e83";
  revCount = 1399;
  shortRev = "431a4a4";
  submodules = false;
}

It's just plain contextless strings so unless I'm fundamentally misunderstanding things, no dragons lie therein.
From here the user is empowered to do as much or as little as she wants with it: use builtins.getFlake for a flake, builtins.fetchTree for a non-flake, or ignore it altogether.

See tests/flakes-with-submodules.sh for a (rudimentary) example of how this might be used within a flake.

This could potentially be used as a basis for a more "flakeful" UX, where submodules behave like indirect (registry) inputs and get populated with the Right Thing if and only if they get added to the outputs function args set... or not.

Since my C++ is rusty and my familiarity with the Nix codebase is flakey (both puns intended btw 🙃), I invite y'all to punch holes in my reasoning and point out any blind spots so that we can address them and hopefully reach a solution that everyone's happy with.

I trust that this would save the sanity of at least a handful of Nixers/Nixresses out there who are forced to interact with git submodules against their better judgement (or in accordance with their poor judgement. to each their own 🤷‍♀️), thereby empowering them to once again pursue their (title-cased) Hopes and Dreams!

kk 'nuff prose. known issues/caveats:

this does add the submodule data to the cache, so a rm -rf ~/.cache/nix is required (otherwise you'd get error: input attribute 'modules' is missing)
~~dirty submodule scenario isn't handled yet~~ added, and fixed so that it also works without __contentAddressed = true; (thanks @shlevy!)
does not solve the "I want self to have submodules = true;" use case (Support self-fetching parameters in flake.nix #5312)
might segfault, murder your kittens or both

Shout out to @cleverca22 for essentially onboarding me to the codebase (... and writing most of the harder parts)

Cheers

Kha

Very cool. I had something like this in mind as well, but then decided for the simpler approach in #5399 for now.

Kha · 2021-11-05T07:41:53Z

src/libfetchers/git.cc

+{
+    auto rootTree = getRootTree(path, gitrev);
+    printTalkative("root tree is %s", rootTree);
+    auto entries = gitTreeList(path, rootTree);


Is this double git cat-file different from git ls-tree $rev?

Idk
/cc @cleverca22

looks like you can just skip directly to ls-tree on a rev

but you still need to recurse manually, git ls-tree $rev $path/ for each dir

Kha · 2021-11-05T07:51:12Z

src/libfetchers/git.cc

+  return results;
+}
+
+std::map<string,string> parseSubmodules(const string & contents) {


Since .gitmodules is technically an arbitrarily formatted git config file, it might be nicer to have git parse the file into a stricter format, which can also be combined with locating & reading the blob: git config --blob $rev:.gitmodules --list

That's a very neat trick thank you!

Kha · 2021-11-05T07:59:07Z

src/libfetchers/git.cc

+  return results;
+}
+
+string findCommitHash(const Path & path, const std::map<string, std::pair<gitType, string>> & _entries, const string & pathToFind) {


I think git ls-tree $rev $submodulePath gives you the same information.

ahhh, and that solves the recursion i mentioned a few comments up

Kha · 2021-11-05T08:21:02Z

src/libfetchers/git.cc

+          prefix = prefix + "file://";
+
+
+      attrs.emplace(subPath, prefix + url + "?allRefs=1&rev=" + commitHash);


If the submodule commit is available only in the local clone and not in the remote, we need to pass the former + submodule path as url here I think.

Actually we should probably always do this if the commit is locally available to avoid redundant fetches

knedlsepp · 2021-11-05T08:57:10Z

Would this be able to handle nested submodules?

kaii-zen · 2021-11-05T14:29:00Z

Would this be able to handle nested submodules?

Not as conveniently as it would be with simply enabling submodules for self. In my understanding the only way to achieve that is by enabling it across the board, which we cannot because it breaks existing workflows.

The happy use case here is when each of your submodules is a flake itself, handling its own submodules without you having to care about it.

With other use cases, such as requiring the recursively cloned source tree for the build itself, you'd have to write some nix code to manipulate the URL provided into an attrset (until #5434 adds &submodule=1 support) to which you'd // { submodule = true; } before passing it along to builtins.fetchTree. Somewhat ugly but works and can be factored out, tucked away and reused when necessary. IMHO this is still 100% better than the current state of affairs where you're simply out of luck 🤷‍♀️

shlevy · 2021-12-02T10:19:27Z

tests/flakes-with-submodules.sh

+fi
+
+clearStore
+rm -rf $TEST_HOME/.{cache,config}


There's clearCache... Why do you need to nuke config?

This part was just copied verbatim from flakes.sh

not necessarily necessary but it helps me wrap my head around things

oddly this doesn't reproduce the problem I'm experiencing IRL where "dirtying" the submodule has no effect until the cache is either nuked or runs out of TTL

This allows changes to dirty submodules to propagate correctly and trigger a re-eval as one would expect. This previously only worked with `__contentAddressed = true;`.

shlevy · 2021-12-06T18:09:43Z

src/libfetchers/fetchers.cc

@@ -257,6 +257,13 @@ std::optional<time_t> Input::getLastModified() const
    return {};
 }

+std::optional<std::string> Input::getModules() const
+{
+    if (auto s = maybeGetStrAttr(attrs, "modules"))


I'm surprised that this works... Isn't modules an attrset? Doesn't maybeGetStrAttr throw if the attribute isn't a string?

It's already stored as JSON. fetchTree reconstructs it into an attrset here: https://github.com/NixOS/nix/pull/5497/files#diff-e473b01a82cc31e51baa89b26b4fe5083e56df27cd834b9722789841ef9d5620R38-R50

not the prettiest thing in the world but it works 🤷‍♀️

😱

Does the process producing the JSON sort keys?

oops, you're right. we only sort in fetchTree 😅

Hmmm... looks like nlohmann takes care of it, unless I'm missing something: https://json.nlohmann.me/features/object_order/

FlorianFranzen · 2022-01-22T16:05:08Z

I rebased this on the latest master and pushed it to my fork under FlorianFranzen/nix/submodules. I have started using this instead of loading submodules by default and it safes me a lot of rebuilds. Would love to have getTree lazyly execute when I access any modules, otherwise I think it is a great first step in submodule support.

kaii-zen · 2022-01-24T15:33:34Z

I rebased this on the latest master and pushed it to my fork under FlorianFranzen/nix/submodules. I have started using this instead of loading submodules by default and it safes me a lot of rebuilds. Would love to have getTree lazyly execute when I access any modules, otherwise I think it is a great first step in submodule support.

We actually did try to implement that using a thunk at some point but it ended up causing an infinite recursion (IIRC) so was reverted and scoped out... December kinda forced a context switch and I haven't had the time to re-wrap my head around this but I really want to see this through as it's been a recurring pain point in my workflow. Anyways I'm happy it's useful. Help me draw more attention 😎

FlorianFranzen · 2022-02-03T21:34:39Z

@cleverca22 Any chance we could get some input on this? I see you did some earlier reviews.

I will have a look at how to implement a lazy version of this. If necessary I could also add an experimental feature flag for it.

I would also like to see this integrated with nix flake metadata.

FlorianFranzen · 2022-02-03T21:55:18Z

tests/fetchGit.sh

@@ -37,6 +37,8 @@ path0_=$(nix eval --impure --raw --expr "(builtins.fetchTree { type = \"git\"; u
 export _NIX_FORCE_HTTP=1
 [[ $(tail -n 1 $path0/hello) = "hello" ]]

+ls -l $repo
+nix eval --debug --impure --raw --expr "(builtins.fetchGit file://$repo).outPath"


Are these really needed?

Looks like debugging leftovers

dmadisetti

Really excited for this change. Please let us know if any additional support is needed- but this looks fine to me

dmadisetti · 2022-03-16T07:28:48Z

tests/fetchGit.sh

@@ -37,6 +37,8 @@ path0_=$(nix eval --impure --raw --expr "(builtins.fetchTree { type = \"git\"; u
 export _NIX_FORCE_HTTP=1
 [[ $(tail -n 1 $path0/hello) = "hello" ]]

+ls -l $repo
+nix eval --debug --impure --raw --expr "(builtins.fetchGit file://$repo).outPath"


Looks like debugging leftovers

Smaug123 · 2022-04-27T18:08:44Z

src/libfetchers/git.cc

+  commit
+};
+
+string getBlob(const Path & path, const string & gitrev, const string & blobhash) {


Forgive my ignorance, but is there a reason this isn't static (given that getRootTree is)?

Probably because I suck at C++. @cleverca22 do you have a better answer? 😅

Smaug123 · 2022-04-27T18:12:54Z

tests/flakes-with-submodules.sh

+git -C $flakeWithSubmodules submodule add $nonFlakeDir
+git -C $flakeWithSubmodules submodule add $flakeDir
+git -C $flakeWithSubmodules add .
+git -C $flakeWithSubmodules commit -m'add submodules'


If I were being a Mighty Stickler I'd request a test that declares this feature's behaviour in the presence of recursive submodules. (That is, repo A has a submodule B, which itself has a submodule C.)

(Ah, I see you commented above that this isn't really supported. And anyway I wouldn't consider this blocking!)

Smaug123 · 2022-04-27T18:29:09Z

src/libfetchers/git.cc

+}
+
+/* Check whether this repo has any commits. There are
+   probably better ways to do this. */


Strictly speaking there's a hilarious but more correct answer:

git cat-file --batch-check='%(objecttype)' --batch-all-objects --unordered | grep commit

But I'm sure any sane repo is in fact going to have an entry in /refs/heads.

Smaug123 · 2022-05-14T12:21:26Z

Does anyone know any blockers for this going in? And/or who has The Power To Merge?

gregistech · 2022-06-28T17:24:05Z

Would love to see this implemented for secrets management.

dmadisetti · 2022-06-28T17:36:24Z

@thegergo02 A bit of a hack now for submodule secrets management is to reference a local "fake flake" and then override it with --override-input secret_flake submodule/path

Fake flake example: https://github.com/dmadisetti/.dots/blob/template/nix/spoof/flake.nix (I have a bit of templating stuff around it)
Main Flake: https://github.com/dmadisetti/.dots/blob/2c8b22900aa368f285a8eef88d658c2ffc01d48b/flake.nix#L33

Smaug123 · 2022-06-29T07:17:01Z

Oh yuck, the merge with master is pretty hairy :(

FlorianFranzen · 2022-10-28T10:42:16Z

I do not mind putting in the work to get this rebased onto master. But I will need some feedback if this is something that actually has a chance of being merged.

And given the ongoing work on #6530, it probably also makes sense to wait till that is merged.

kaii-zen · 2022-10-28T17:01:17Z

I do not mind putting in the work to get this rebased onto master. But I will need some feedback if this is something that actually has a chance of being merged.

And given the ongoing work on #6530, it probably also makes sense to wait till that is merged.

Makes two of us 🤭

Ericson2314 · 2023-08-04T20:41:29Z

Triaged in the Nix Team meeting this morning (n.b. I could not make it):

One part might be obsolete given some changes on master. @edolstra will enquire.
The rest (exposing the submodules at the Nix level) should be discussed

nixos-discourse · 2023-08-09T05:14:16Z

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2023-08-04-nix-team-meeting-minutes-77/31487/1

fricklerhandwerk · 2023-10-20T17:14:58Z

Discussed in Nix team meeting 2023-10-13:

Shouldn't be a blocker for stabilizing fetchTree
- Maybe submodules should be experimental then
The lazy-trees branch has another solution for that (as part of the libgit rewrite), could be backported
- Similar idea overall
- @edolstra wants to open a first PR for that today
@edolstra: Prefer the libgit approach
Decision: The tests are great and should be incorporated. The rest is very likely conflicting with the planned libgit rewrite.

@FlorianFranzen @kaii-zen @Ericson2314 would one of you be interested in splitting out the tests?

nixos-discourse · 2023-10-20T17:30:37Z

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2023-10-13-nix-team-meeting-minutes-94/34395/1

This was referenced Nov 4, 2021

Support building flakes from a Git repo url with submodules #5434

Merged

Optimize submodules fetching #5399

Closed

nix flakes: add support for git submodules #4423

Closed

kaii-zen marked this pull request as ready for review November 4, 2021 19:01

Kha reviewed Nov 5, 2021

View reviewed changes

kaii-zen force-pushed the submodules branch from e671a4b to b8ae0ab Compare November 6, 2021 01:57

shlevy reviewed Dec 2, 2021

View reviewed changes

kaii-zen force-pushed the submodules branch from 9b4e01a to 74e7bcb Compare December 2, 2021 16:43

Shay Bergmann and others added 17 commits December 2, 2021 17:24

implement passing submodules information when tree is not dirty

03e71c5

parse the cat-file output to find the submodules

4d6b738

serialize submodule info into the cache

73bbc24

Fix fetchGit.sh tests

d54d8ec

Get flake.sh tests to pass

2c9ec9d

Fix wrong path

1ca14d5

Fix dirty tree scenario

f5fa4b0

Explicitly add file:// when bare path is given

28d6715

Add test to demonstrate

2ff9b20

Add tests for unclean submodule state

b2bf6cc

Factor out some logic I might need

594a51e

not necessarily necessary but it helps me wrap my head around things

Implement support for unclean submodule scenario

f55b99f

printTalkative spam

ce081f0

Fix wrong repo path

124e703

Support specifying branch in .gitmodules

50d13e7

Test recomposing source with submodules

551cb98

oddly this doesn't reproduce the problem I'm experiencing IRL where "dirtying" the submodule has no effect until the cache is either nuked or runs out of TTL

Add the submodule info to flake fingerprint

c2cde79

This allows changes to dirty submodules to propagate correctly and trigger a re-eval as one would expect. This previously only worked with `__contentAddressed = true;`.

kaii-zen force-pushed the submodules branch from 74e7bcb to c2cde79 Compare December 6, 2021 16:40

shlevy reviewed Dec 6, 2021

View reviewed changes

FlorianFranzen reviewed Feb 3, 2022

View reviewed changes

dmadisetti reviewed Apr 5, 2022

View reviewed changes

Smaug123 reviewed Apr 27, 2022

View reviewed changes

MagicRB mentioned this pull request May 24, 2022

Impl: Propagate Flake inputs #6550

Open

RCoeurjoly mentioned this pull request Jun 6, 2022

[WIP] Add nix flake to provide development shell coq-universe/coq-universe#15

Merged

akirak mentioned this pull request Jan 7, 2023

taxy/taxy-magit-section split alphapapa/taxy.el#3

Open

fricklerhandwerk added the flakes label Mar 3, 2023

		prefix = prefix + "file://";


		attrs.emplace(subPath, prefix + url + "?allRefs=1&rev=" + commitHash);

A different take on git submodule support for flakes #5497

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A different take on git submodule support for flakes #5497

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kaii-zen commented Nov 4, 2021 • edited Loading

Idea

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Kha Nov 5, 2021 • edited Loading

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FlorianFranzen commented Jan 22, 2022

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Smaug123 Apr 27, 2022 • edited Loading

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Smaug123 commented May 14, 2022

gregistech commented Jun 28, 2022

dmadisetti commented Jun 28, 2022

Smaug123 commented Jun 29, 2022

FlorianFranzen commented Oct 28, 2022

kaii-zen commented Oct 28, 2022

Ericson2314 commented Aug 4, 2023

nixos-discourse commented Aug 9, 2023

fricklerhandwerk commented Oct 20, 2023

nixos-discourse commented Oct 20, 2023

kaii-zen commented Nov 4, 2021 •

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