Merge pull request #5479 from NixOS/selfref-ca

Fix the removal of ca-induced self-references

src/libstore/ca-specific-schema.sql

@@ -13,12 +13,27 @@ 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 in (
+      select id from Realisations where outputPath = old.id
+    );
+  end;
+
 create table if not exists RealisationsRefs (
     referrer integer not null,
     realisationReference integer,
     foreign key (referrer) references Realisations(id) on delete cascade,
     foreign key (realisationReference) references Realisations(id) on delete restrict
 );
+-- used by deletion trigger
+create index if not exists IndexRealisationsRefsRealisationReference on RealisationsRefs(realisationReference);
 
 -- used by QueryRealisationReferences
 create index if not exists IndexRealisationsRefs on RealisationsRefs(referrer);

src/libstore/local-store.cc

@@ -81,7 +81,7 @@ int getSchema(Path schemaPath)
 
 void migrateCASchema(SQLite& db, Path schemaPath, AutoCloseFD& lockFd)
 {
-    const int nixCASchemaVersion = 3;
+    const int nixCASchemaVersion = 4;
     int curCASchema = getSchema(schemaPath);
     if (curCASchema != nixCASchemaVersion) {
         if (curCASchema > nixCASchemaVersion) {
@@ -143,6 +143,21 @@ void migrateCASchema(SQLite& db, Path schemaPath, AutoCloseFD& lockFd)
             )");
             txn.commit();
         }
+        if (curCASchema < 4) {
+            SQLiteTxn txn(db);
+            db.exec(R"(
+                create trigger if not exists DeleteSelfRefsViaRealisations before delete on ValidPaths
+                begin
+                    delete from RealisationsRefs where realisationReference in (
+                    select id from Realisations where outputPath = old.id
+                    );
+                end;
+                -- used by deletion trigger
+                create index if not exists IndexRealisationsRefsRealisationReference on RealisationsRefs(realisationReference);
+            )");
+            txn.commit();
+        }
+
         writeFile(schemaPath, fmt("%d", nixCASchemaVersion));
         lockFile(lockFd.get(), ltRead, true);
     }

tests/build-remote-content-addressed-floating.sh

@@ -2,7 +2,7 @@ source common.sh
 
 file=build-hook-ca-floating.nix
 
-enableFeatures "ca-derivations ca-references"
+enableFeatures "ca-derivations"
 
 CONTENT_ADDRESSED=true
 

tests/ca/common.sh

@@ -1,5 +1,5 @@
 source ../common.sh
 
-enableFeatures "ca-derivations ca-references"
+enableFeatures "ca-derivations"
 
 restartDaemon

tests/ca/selfref-gc.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+
+source common.sh
+
+requireDaemonNewerThan "2.4pre20210626"
+
+enableFeatures "ca-derivations nix-command flakes"
+
+export NIX_TESTS_CA_BY_DEFAULT=1
+cd ..
+source ./selfref-gc.sh

tests/local.mk

@@ -92,6 +92,7 @@ nix_tests = \
   plugins.sh \
   build.sh \
   ca/nix-run.sh \
+  selfref-gc.sh ca/selfref-gc.sh \
   db-migration.sh \
   bash-profile.sh \
   pass-as-file.sh \

tests/nix-profile.sh

@@ -3,7 +3,7 @@ source common.sh
 clearStore
 clearProfiles
 
-enableFeatures "ca-derivations ca-references"
+enableFeatures "ca-derivations"
 restartDaemon
 
 # Make a flake.

tests/selfref-gc.sh

@@ -0,0 +1,30 @@
+source common.sh
+
+requireDaemonNewerThan "2.6.0pre20211215"
+
+clearStore
+
+nix-build --no-out-link -E '
+  with import ./config.nix;
+
+  let d1 = mkDerivation {
+    name = "selfref-gc";
+    outputs = [ "out" ];
+    buildCommand = "
+      echo SELF_REF: $out > $out
+    ";
+  }; in
+
+  # the only change from d1 is d1 as an (unused) build input
+  # to get identical store path in CA.
+  mkDerivation {
+    name = "selfref-gc";
+    outputs = [ "out" ];
+    buildCommand = "
+      echo UNUSED: ${d1}
+      echo SELF_REF: $out > $out
+    ";
+  }
+'
+
+nix-collect-garbage