Set all Nix builder runtime vars for devx wrapper outside builds

setup.sh runs with set -eu and expects NIX_BUILD_TOP, TMPDIR, out,
and other variables that the Nix builder sets at runtime. The
previous fix only set $out; NIX_BUILD_TOP was the next failure.

Set all required builder runtime variables (NIX_BUILD_TOP, TMPDIR,
TMP, TEMP, TEMPDIR, NIX_STORE, out) in both mkEnvScript and the
CI validate step.

Verified locally on hydra: both static (ghc96-static-env) and
dynamic (ghc98-minimal-env) wrappers work correctly.

Author: angerman

.github/workflows/pr-validate.yml

@@ -104,10 +104,17 @@ jobs:
         echo "Cabal: $(cabal --version 2>/dev/null | head -1 || echo N/A)"
         TESTEOF
 
-        # stdenv's setup.sh requires $out for output variable assignment.
-        # Inside a Nix build $out is set automatically; when running
-        # directly we must provide a dummy value.
-        export out=$(mktemp -d)
+        # stdenv's setup.sh expects Nix builder runtime variables
+        # (NIX_BUILD_TOP, out, etc.) that only exist inside nix build.
+        # Provide them so the devx wrapper can source setup.sh.
+        export NIX_BUILD_TOP="$(mktemp -d)"
+        export TMPDIR="$NIX_BUILD_TOP"
+        export TMP="$NIX_BUILD_TOP"
+        export TEMP="$NIX_BUILD_TOP"
+        export TEMPDIR="$NIX_BUILD_TOP"
+        export NIX_STORE="/nix/store"
+        export out="$NIX_BUILD_TOP/out"
+        mkdir -p "$out"
         "$DEVX_PATH" "$SMOKE_TEST"
         echo "::endgroup::"
 

flake.nix

@@ -349,12 +349,18 @@
                   # attributes needed to initialize the full dev environment.
                   ${envExports}
 
-                  # setup.sh requires $out for output variable assignment
-                  # (_assignFirst). Inside a Nix build $out is set by the
-                  # builder; when running directly (container, CLI) we
-                  # provide a temporary directory so setup.sh succeeds.
-                  if [ -z "''${out:-}" ]; then
-                    export out=$(mktemp -d)
+                  # setup.sh expects Nix builder runtime variables that are
+                  # only set inside `nix build`. When running directly
+                  # (container, CI, CLI) we provide sensible defaults.
+                  if [ -z "''${NIX_BUILD_TOP:-}" ]; then
+                    export NIX_BUILD_TOP="$(mktemp -d)"
+                    export TMPDIR="$NIX_BUILD_TOP"
+                    export TMP="$NIX_BUILD_TOP"
+                    export TEMP="$NIX_BUILD_TOP"
+                    export TEMPDIR="$NIX_BUILD_TOP"
+                    export NIX_STORE="/nix/store"
+                    export out="$NIX_BUILD_TOP/out"
+                    mkdir -p "$out"
                   fi
 
                   # Source stdenv's setup.sh to initialize the development