From ef03df0af156df7179e31569725de314990e74ea Mon Sep 17 00:00:00 2001
From: Maximilian Bosch <maximilian@mbosch.me>
Date: Fri, 26 Jan 2024 16:57:37 +0100
Subject: [PATCH 1/2] Build: use `nix path-info` to test for build output
 availability

When using the Perl bindings, this usually takes the wrong store, i.e.
`auto` even if `store_uri` is a flat-file binary cache.

See also https://github.com/NixOS/nix/issues/9859

Using fork/exec here on purpose to make sure that the output of `nix path-info`
isn't spammed into stderr. This could probably done with
`system("foo &>/dev/null")`, but I didn't want to worry about shell
injection issues then. And finally, I can't seem to silence STDERR for
`system` with a list as argument. Not a Perl dev though, so not sure if
there's a better way.
---
 src/lib/Hydra/Controller/Build.pm | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/lib/Hydra/Controller/Build.pm b/src/lib/Hydra/Controller/Build.pm
index c3869838d..22f3c797f 100644
--- a/src/lib/Hydra/Controller/Build.pm
+++ b/src/lib/Hydra/Controller/Build.pm
@@ -71,6 +71,17 @@ sub findBuildStepByDrvPath {
 
 sub build :Chained('buildChain') :PathPart('') :Args(0) :ActionClass('REST') { }
 
+sub isValidPathNixCLI {
+    my $path = shift;
+    my $pid = fork();
+    if (!$pid) {
+        open STDERR, ">", "/dev/null";
+        exec "nix", "path-info", $path, "--store", getStoreUri();
+    }
+    waitpid $pid, 0;
+    return $? == 0;
+}
+
 sub build_GET {
     my ($self, $c) = @_;
 
@@ -82,7 +93,7 @@ sub build_GET {
     # false because `$_->path` will be empty
     $c->stash->{available} =
         $c->stash->{isLocalStore}
-        ? all { $_->path && isValidPath($_->path) } $build->buildoutputs->all
+        ? all { $_->path && isValidPathNixCLI($_->path) } $build->buildoutputs->all
         : 1;
     $c->stash->{drvAvailable} = isValidPath $build->drvpath;
 

From 15b7d91b512ce565319ecbf6c6fa63f408ea41a9 Mon Sep 17 00:00:00 2001
From: Maximilian Bosch <maximilian@mbosch.me>
Date: Fri, 26 Jan 2024 18:57:47 +0100
Subject: [PATCH 2/2] Build: enable nix-command on `nix path-info` call,
 silence stdout as well

`nix-store -q` (and `--outputs`) doesn't seem to complain if a path
doesn't exist in a store anymore, so let's do it that way.

This approach works fine on Nix 2.3 as well, it only warns about
`experimental-features` being an unknown option, but that's silenced
along with the rest of stderr.
---
 src/lib/Hydra/Controller/Build.pm | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/lib/Hydra/Controller/Build.pm b/src/lib/Hydra/Controller/Build.pm
index 22f3c797f..003cf0c59 100644
--- a/src/lib/Hydra/Controller/Build.pm
+++ b/src/lib/Hydra/Controller/Build.pm
@@ -76,7 +76,8 @@ sub isValidPathNixCLI {
     my $pid = fork();
     if (!$pid) {
         open STDERR, ">", "/dev/null";
-        exec "nix", "path-info", $path, "--store", getStoreUri();
+        open STDOUT, ">", "/dev/null";
+        exec "nix", "path-info", $path, "--store", getStoreUri(), "--option", "experimental-features", "nix-command";
     }
     waitpid $pid, 0;
     return $? == 0;