Fix the gc with indirect self-references via the realisations

If the derivation `foo` depends on `bar`, and they both have the same
output path (because they are CA derivations), then this output path
will depend both on the realisation of `foo` and of `bar`, which
themselves depend on each other.
This confuses SQLite which isn’t able to automatically solve this
diamond dependency scheme.

Help it by adding a trigger to delete all the references between the
relevant realisations.

Fix #5320

1 files changed, 13 insertions, 0 deletions

diff --git a/src/libstore/ca-specific-schema.sql b/src/libstore/ca-specific-schema.sql
index 64cc97fde..d2ea347fb 100644
--- a/src/libstore/ca-specific-schema.sql
+++ b/src/libstore/ca-specific-schema.sql
@@ -13,6 +13,19 @@ create table if not exists Realisations (
 
 create index if not exists IndexRealisations on Realisations(drvPath, outputName);
 
+-- We can end-up in a weird edge-case where a path depends on itself because
+-- it’s an output of a CA derivation, that happens to be the same as one of its
+-- dependencies.
+-- In that case we have a dependency loop (path -> realisation1 -> realisation2
+-- -> path) that we need to break by removing the dependencies between the
+-- realisations
+create trigger if not exists DeleteSelfRefsViaRealisations before delete on ValidPaths
+  begin
+    delete from RealisationsRefs where realisationReference = (
+      select id from Realisations where outputPath = old.id
+    );
+  end;
+
 create table if not exists RealisationsRefs (
     referrer integer not null,
     realisationReference integer,