exportReferencesGraph started including a valid: true field

[flokli]

Describe the bug

I started writing some types for the reference graph structure that Nix emits when its exportReferencesGraph feature is used.

I initially included the valid boolean (which seems to be always true).

I then triggered the build on another machine running an older version of Nix (2.3), and my parsing code failed, as the valid field was not present.

While probably not too much code relies on this, and instead looks at individual fields it knows to be present, we should produce the same JSON across versions. It'd be good if this output stays consistent across versions, and the additional field in there gets removed again.

Steps To Reproduce

Build stdenv.mkDerivation { name = "hello"; __structuredAttrs = true; exportReferencesGraph.blub = [ pkgs.hello ]; nativeBuildInputs = [pkgs.jq]; buildCommand = "jq -rc .blub $NIX_ATTRS_JSON_FILE > $out"; } on a machine with current Nix, and on one with Nix 2.3. Observe how the resulting output differs and the Nix version used is observable through that.

Priorities

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[Kranzes]

Potentially caused by #9242

[flokli]

That PR description even mentions the stability in structured attrs:

This keeps the human oriented CLI logic (which is currently stable) and the core domain logic (export reference graphs with structured attrs, which is stable), separate, which I think is better.

[tomberek]

New output has a "valid" field.

  {
    "closureSize": 2216152,
    "narHash": "sha256:0z1mdik09afiskvxjzcxl60sq0rzvh7lx6a7hxs2q1s379r6n1n5",
    "narSize": 358784,
    "path": "/nix/store/w4djxksksd1p8m054k537plqnif5858k-libidn2-2.3.4",
    "references": [
      "/nix/store/4r64z7v5l40pg6r0hd169bcs85c8c42b-libunistring-1.1",
      "/nix/store/w4djxksksd1p8m054k537plqnif5858k-libidn2-2.3.4"
    ],
    "valid": true
  }

Perhaps just:

diff --git a/src/libstore/parsed-derivations.cc b/src/libstore/parsed-derivations.cc
index 72f45143d..09801919f 100644
--- a/src/libstore/parsed-derivations.cc
+++ b/src/libstore/parsed-derivations.cc
@@ -151,8 +151,6 @@ static nlohmann::json pathInfoToJSON(
         // Add the path to the object whose metadata we are including.
         jsonPath["path"] = store.printStorePath(storePath);

-        jsonPath["valid"] = true;
-
         jsonPath["closureSize"] = ({
             uint64_t totalNarSize = 0;
             StorePathSet closure;

[Ericson2314]

This issue has been present since f86f2b9 (merged Mar 2, 2023), when someone thought they were just updating the command-line interface but actually were also changing this feature.

My #9242 tried to separate these two use-cases somewhat, which just made the oddity more visible.