Minimal repro for functional test failures in Nix under macOS

minimal-repro.sh

#!/usr/bin/env bash

echo "=============================================="
echo "Minimal Reproduction: macOS Shebang Bug"
echo "=============================================="
echo ""
echo "Platform: $(uname -s) $(uname -m)"
echo "Nix version: $(nix --version)"
echo ""

# Test WITHOUT shebang
echo "=== Testing WITHOUT shebang (expect ~20% SIGSEGV) ==="
passed=0
failed=0

for i in $(seq 1 10); do
  timestamp=$(date +%s%N)

  cat > /tmp/no-shebang-test-$i.nix << EOF
{ pkgs ? import <nixpkgs> {} }:
let
  # Script WITHOUT shebang - like tests/functional/shell.nix
  fooNoShebang = pkgs.runCommand "foo-$timestamp" {} ''
    mkdir -p \$out/bin
    echo 'echo foo' > \$out/bin/foo
    chmod a+rx \$out/bin/foo
  '';
in pkgs.runCommand "test-$timestamp" {
  nativeBuildInputs = [ pkgs.bash pkgs.coreutils fooNoShebang ];
} ''
  set -e
  mkdir -p \$out
  export PATH="\${fooNoShebang}/bin:\$PATH"

  # Run foo in subshell capture (like the actual tests do)
  result=\$(foo)
  if [ "\$result" != "foo" ]; then
    exit 1
  fi
  echo "ok" > \$out/result
''
EOF

  result=$(nix-build /tmp/no-shebang-test-$i.nix --no-out-link 2>&1)
  exit_code=$?

  if [ $exit_code -eq 0 ]; then
    ((passed++))
    echo -n "."
  else
    ((failed++))
    if echo "$result" | grep -q "exit code 139"; then
      echo -n "X"  # SIGSEGV
    else
      echo -n "!"  # Other error
    fi
  fi

  rm -f /tmp/no-shebang-test-$i.nix
done

echo ""
echo "Results: $passed/10 passed, $failed/10 failed"
echo ""

# Test WITH shebang
echo "=== Testing WITH shebang (expect 100% success) ==="
passed=0
failed=0

for i in $(seq 1 10); do
  timestamp=$(date +%s%N)

  cat > /tmp/with-shebang-test-$i.nix << EOF
{ pkgs ? import <nixpkgs> {} }:
let
  shell = "\${pkgs.bash}/bin/bash";

  # Script WITH shebang - the fix
  fooWithShebang = pkgs.runCommand "foo-fixed-$timestamp" {} ''
    mkdir -p \$out/bin
    echo '#!'\${shell} > \$out/bin/foo
    echo 'echo foo' >> \$out/bin/foo
    chmod a+rx \$out/bin/foo
  '';
in pkgs.runCommand "test-fixed-$timestamp" {
  nativeBuildInputs = [ pkgs.bash pkgs.coreutils fooWithShebang ];
} ''
  set -e
  mkdir -p \$out
  export PATH="\${fooWithShebang}/bin:\$PATH"

  result=\$(foo)
  if [ "\$result" != "foo" ]; then
    exit 1
  fi
  echo "ok" > \$out/result
''
EOF

  result=$(nix-build /tmp/with-shebang-test-$i.nix --no-out-link 2>&1)
  exit_code=$?

  if [ $exit_code -eq 0 ]; then
    ((passed++))
    echo -n "."
  else
    ((failed++))
    echo -n "X"
  fi

  rm -f /tmp/with-shebang-test-$i.nix
done

echo ""
echo "Results: $passed/10 passed, $failed/10 failed"
echo ""