Fix missing GC root in zipAttrsWith

[edolstra]

Motivation

Fixes #11547.

My SNAFU was that I assumed that all the Value *s we put in attrsSeen are already reachable (which they are), but I forgot about the elems pointer in ListBuilder.

Thanks to @puckipedia and @yorickvP for diagnosing.

Context

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[Mic92]

Fixes the the issue for me. nix 2.24 crashes in 10s

#!/usr/bin/env nix-shell
#!nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/4b87f8820eba50283dbcc38442d49439a4117529.tar.gz -i bash -p nix parallel rr
set -e

SCRIPT_DIR=$(dirname -- "$0";)
RRDIR="$SCRIPT_DIR/rr-testing"
cd "$SCRIPT_DIR"
export GC_FREE_SPACE_DIVISOR=69 GC_ENABLE_INCREMENTAL=1

gorun() {
    for (( i=0; i < 80; i = i + 1 )); do
        #_RR_TRACE_DIR=$RRDIR parallel -N0 --verbose --halt-on-error 2 --lb rr record --chaos -- nix eval --eval-store "$(pwd)/store" -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/4b87f8820eba50283dbcc38442d49439a4117529.tar.gz  -I nixos-config=./configuration.nix -f '"<nixpkgs/nixos>"' config.system.build.toplevel ::: {1..80}
        #parallel -N0 --verbose --halt-on-error 2 --lb /nix/store/qi0z5ar7ln3ahmnnd2336221bz5zm2zn-nix-2.25.0pre20240919_75dc688/bin/nix eval --eval-store "$(pwd)/store" -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/4b87f8820eba50283dbcc38442d49439a4117529.tar.gz  -I nixos-config=./configuration.nix -f '"<nixpkgs/nixos>"' config.system.build.toplevel ::: {1..80}
        parallel -N0 --verbose --halt-on-error 2 --lb nix eval --eval-store "$(pwd)/store" -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/4b87f8820eba50283dbcc38442d49439a4117529.tar.gz  -I nixos-config=./configuration.nix -f '"<nixpkgs/nixos>"' config.system.build.toplevel ::: {1..80}
    done
}

nix --version

while true; do
    rm -rvf "$RRDIR"
    gorun
done

This script keeps running:

#!/usr/bin/env nix-shell
#!nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/4b87f8820eba50283dbcc38442d49439a4117529.tar.gz -i bash -p nix parallel rr
set -e

SCRIPT_DIR=$(dirname -- "$0";)
RRDIR="$SCRIPT_DIR/rr-testing"
cd "$SCRIPT_DIR"
export GC_FREE_SPACE_DIVISOR=69 GC_ENABLE_INCREMENTAL=1

gorun() {
    for (( i=0; i < 80; i = i + 1 )); do
        parallel -N0 --verbose --halt-on-error 2 --lb /nix/store/qi0z5ar7ln3ahmnnd2336221bz5zm2zn-nix-2.25.0pre20240919_75dc688/bin/nix eval --eval-store "$(pwd)/store" -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/4b87f8820eba50283dbcc38442d49439a4117529.tar.gz  -I nixos-config=./configuration.nix -f '"<nixpkgs/nixos>"' config.system.build.toplevel ::: {1..80}
    done
}

nix --version

while true; do
    rm -rvf "$RRDIR"
    gorun
done