tests: implement test for nix log with ssh-ng:// builds

A few notes:

* The `echo hi` is needed to make sure that a file that can be read by
  `nix log` is properly created (i.e. some output is needed). This is
  known and to be fixed in #6051.
* We explicitly ignore the floating-CA case here: the `$out` of `input3`
  depends on `$out` of `input2`. This means that there are actually two
  derivations - I assume that this is because at eval time (i.e.
  `nix-instantiate -A`) the hash of `input2` isn't known yet and the
  other .drv is created as soon as `input2` was built. This is another
  issue on its own, so we ignore the case here explicitly.

tests/build-hook-ca-fixed.nix

@@ -11,13 +11,13 @@ let
       args = ["sh" "-e" args.builder or (builtins.toFile "builder-${args.name}.sh" "if [ -e .attrs.sh ]; then source .attrs.sh; fi; eval \"$buildCommand\"")];
       outputHashMode = "recursive";
       outputHashAlgo = "sha256";
-    } // removeAttrs args ["builder" "meta"])
-    // { meta = args.meta or {}; };
+    } // removeAttrs args ["builder" "meta" "passthru"])
+    // { meta = args.meta or {}; passthru = args.passthru or {}; };
 
   input1 = mkDerivation {
     shell = busybox;
     name = "build-remote-input-1";
-    buildCommand = "echo FOO > $out";
+    buildCommand = "echo hi; echo FOO > $out";
     requiredSystemFeatures = ["foo"];
     outputHash = "sha256-FePFYIlMuycIXPZbWi7LGEiMmZSX9FMbaQenWBzm1Sc=";
   };
@@ -25,7 +25,7 @@ let
   input2 = mkDerivation {
     shell = busybox;
     name = "build-remote-input-2";
-    buildCommand = "echo BAR > $out";
+    buildCommand = "echo hi; echo BAR > $out";
     requiredSystemFeatures = ["bar"];
     outputHash = "sha256-XArauVH91AVwP9hBBQNlkX9ccuPpSYx9o0zeIHb6e+Q=";
   };
@@ -34,6 +34,7 @@ let
     shell = busybox;
     name = "build-remote-input-3";
     buildCommand = ''
+      echo hi
       read x < ${input2}
       echo $x BAZ > $out
     '';
@@ -46,6 +47,7 @@ in
   mkDerivation {
     shell = busybox;
     name = "build-remote";
+    passthru = { inherit input1 input2 input3; };
     buildCommand =
       ''
         read x < ${input1}

tests/build-hook.nix

@@ -9,20 +9,20 @@ let
       inherit system;
       builder = busybox;
       args = ["sh" "-e" args.builder or (builtins.toFile "builder-${args.name}.sh" "if [ -e .attrs.sh ]; then source .attrs.sh; fi; eval \"$buildCommand\"")];
-    } // removeAttrs args ["builder" "meta"])
-    // { meta = args.meta or {}; };
+    } // removeAttrs args ["builder" "meta" "passthru"])
+    // { meta = args.meta or {}; passthru = args.passthru or {}; };
 
   input1 = mkDerivation {
     shell = busybox;
     name = "build-remote-input-1";
-    buildCommand = "echo FOO > $out";
+    buildCommand = "echo hi; echo FOO > $out";
     requiredSystemFeatures = ["foo"];
   };
 
   input2 = mkDerivation {
     shell = busybox;
     name = "build-remote-input-2";
-    buildCommand = "echo BAR > $out";
+    buildCommand = "echo hi; echo BAR > $out";
     requiredSystemFeatures = ["bar"];
   };
 
@@ -30,6 +30,7 @@ let
     shell = busybox;
     name = "build-remote-input-3";
     buildCommand = ''
+      echo hi
       read x < ${input2}
       echo $x BAZ > $out
     '';
@@ -41,6 +42,7 @@ in
   mkDerivation {
     shell = busybox;
     name = "build-remote";
+    passthru = { inherit input1 input2 input3; };
     buildCommand =
       ''
         read x < ${input1}

tests/build-remote.sh

@@ -54,6 +54,14 @@ nix path-info --store $TEST_ROOT/machine3 --all \
   | grep -v builder-build-remote-input-2.sh \
   | grep builder-build-remote-input-3.sh
 
+
+if [[ -z "$CONTENT_ADDRESSED" ]]; then
+  for i in input1 input3; do
+    drv="$(nix-instantiate $file -A passthru.$i --store $TEST_ROOT/machine0 --arg busybox $busybox)"
+    nix log --store $TEST_ROOT/machine0 "$drv"
+  done
+fi
+
 # Behavior of keep-failed
 out="$(nix-build 2>&1 failing.nix \
   --builders "$(join_by '; ' "${builders[@]}")"  \