Remove Cantera from formula - make it an optional user-installed dependency

Cantera's scons build system is incompatible with Homebrew's build
environment (it resets ENV variables). Instead of fighting this, make
Cantera optional and document how users can install it themselves if
needed. Most MFC users don't need Cantera anyway.

Author: sbryngelson

packaging/homebrew/mfc.rb

@@ -19,112 +19,13 @@ class Mfc < Formula
   depends_on "open-mpi"
   depends_on "openblas"
   depends_on "[email protected]"
-  depends_on "sundials"
-  depends_on "yaml-cpp"
-
-  resource "cantera" do
-    url "https://github.com/Cantera/cantera.git",
-        tag: "v3.1.0"
-  end
 
   def install
-    # Create Python virtual environment first (before MFC build)
+    # Create Python virtual environment
     venv = libexec/"venv"
     system Formula["[email protected]"].opt_bin/"python3.12", "-m", "venv", venv
     system venv/"bin/pip", "install", "--upgrade", "pip", "setuptools", "wheel"
 
-    # Build and install Cantera 3.1.0 from source BEFORE MFC build
-    resource("cantera").stage do
-      # Install Cantera build dependencies (including scons)
-      system venv/"bin/pip", "install", "cython", "numpy", "ruamel.yaml", "packaging", "scons"
-
-      # Configure Cantera build
-      # Cantera's scons needs explicit compiler selection and environment variables
-      sdk_path = MacOS.sdk_path
-
-      # Set environment variables that scons will use during compiler checks
-      ENV["CC"] = ENV.cc
-      ENV["CXX"] = ENV.cxx
-      ENV["CFLAGS"] = "-isysroot#{sdk_path}"
-      ENV["CXXFLAGS"] = "-isysroot#{sdk_path} -stdlib=libc++"
-      ENV["SDKROOT"] = sdk_path.to_s
-
-      # Also set include path variables for libc++ headers
-      cxx_inc_path = "#{sdk_path}/usr/include/c++/v1"
-      ENV["CPPFLAGS"] = ["-I#{cxx_inc_path}", ENV.fetch("CPPFLAGS", nil)].compact.join(" ")
-
-      # Run scons, explicitly passing compiler flags as Cantera scons variables
-      # Cantera uses cc_flags/cxx_flags, not CCFLAGS/CXXFLAGS
-      # Include both SDK include path and C++ header path for scons' configuration checks
-      sdk_inc_path = "#{sdk_path}/usr/include"
-      cxx_flags_with_includes = "#{ENV.fetch("CXXFLAGS", nil)} -I#{sdk_inc_path} -I#{cxx_inc_path}"
-
-      # Run scons build - output config.log if it fails
-      sundials_inc = Formula["sundials"].opt_include
-      yamlcpp_inc = Formula["yaml-cpp"].opt_include
-      sundials_lib = Formula["sundials"].opt_lib
-      yamlcpp_lib = Formula["yaml-cpp"].opt_lib
-
-      # Debug: Show what we're about to run
-      opoo "About to run Cantera scons build in: #{Dir.pwd}"
-      opoo "SDK path: #{sdk_path}"
-      opoo "C++ flags: #{cxx_flags_with_includes}"
-
-      success = system venv/"bin/python", "-m", "SCons", "build",
-                       "CC=#{ENV.cc}",
-                       "CXX=#{ENV.cxx}",
-                       "cc_flags=#{ENV.fetch("CFLAGS", nil)} -I#{sdk_inc_path}",
-                       "cxx_flags=#{cxx_flags_with_includes}",
-                       "python_package=y",
-                       "f90_interface=n",
-                       "system_sundials=y",
-                       "system_yamlcpp=y",
-                       "system_fmt=n",
-                       "extra_inc_dirs=#{cxx_inc_path}:#{sundials_inc}:#{yamlcpp_inc}",
-                       "extra_lib_dirs=#{sundials_lib}:#{yamlcpp_lib}",
-                       "prefix=#{libexec}/cantera",
-                       "python_cmd=#{venv}/bin/python",
-                       "-j#{ENV.make_jobs}"
-
-      unless success
-        opoo "=============================================="
-        opoo "Cantera scons build FAILED!"
-        opoo "Current directory: #{Dir.pwd}"
-        opoo "=============================================="
-
-        # Try to find and display config.log
-        config_log_candidates = ["config.log", "build/config.log", ".sconf_temp/conftest.out"]
-        config_log_candidates.each do |candidate|
-          next unless File.exist?(candidate)
-
-          opoo "Found #{candidate}:"
-          File.open(candidate, "r") do |f|
-            puts f.read
-          end
-        end
-
-        # Also search recursively
-        Dir.glob("**/config.log").each do |path|
-          opoo "Found config.log at: #{path}"
-          puts File.read(path)
-        end
-
-        # List directory contents
-        opoo "Directory listing:"
-        system "ls", "-laR"
-
-        odie "Cantera scons build failed - see config.log output above"
-      end
-
-      # Install Cantera
-      system venv/"bin/python", "-m", "SCons", "install"
-
-      # Install Cantera Python package into venv
-      cd "build/python" do
-        system venv/"bin/pip", "install", "--no-build-isolation", "."
-      end
-    end
-
     # Install Python toolchain (needed before build)
     prefix.install "toolchain"
 
@@ -138,113 +39,87 @@ def install
     # Now build MFC with pre-configured venv
     # Set VIRTUAL_ENV so mfc.sh uses existing venv instead of creating new one
     ENV["VIRTUAL_ENV"] = venv
-    ENV["PATH"] = "#{venv}/bin:#{ENV.fetch("PATH", nil)}"
-
-    system "./mfc.sh", "build",
-           "-t", "pre_process", "simulation", "post_process",
-           "-j", ENV.make_jobs
 
-    # Install binaries
-    # MFC installs each binary to a separate hashed subdirectory, find them individually
-    %w[pre_process simulation post_process].each do |binary|
-      binary_paths = Dir.glob("build/install/*/bin/#{binary}")
-      raise "Could not find #{binary}" if binary_paths.empty?
+    # Build MFC using pre-configured venv
+    system "./mfc.sh", "build", "-t", "pre_process", "simulation", "post_process", "-j", ENV.make_jobs.to_s
 
-      bin.install binary_paths.first
+    # Install binaries - they're in hashed subdirectories like build/install/<hash>/bin/*
+    Dir.glob("build/install/*/bin/*").each do |binary_path|
+      bin.install binary_path
     end
 
-    # Install mfc.sh script to libexec
+    # Install main mfc.sh script
     libexec.install "mfc.sh"
 
+    # Install toolchain directory (already done above, but make sure it stays in prefix)
+    # (already done with prefix.install above)
+
     # Install examples
-    pkgshare.install "examples"
+    prefix.install "examples"
 
-    # Create a wrapper that sets up a working environment for mfc.sh
-    # The wrapper uses a temporary directory since Cellar is read-only and
-    # activates the pre-installed Python virtual environment
+    # Create smart wrapper script that:
+    # 1. Works around read-only Cellar issue
+    # 2. Activates venv automatically so cantera/dependencies are available
     (bin/"mfc").write <<~EOS
       #!/bin/bash
       set -e
 
-      # Activate the pre-installed Python virtual environment
-      source "#{libexec}/venv/bin/activate"
-
-      # Create a working directory for MFC in user's cache
-      MFC_WORK_DIR="${TMPDIR:-/tmp}/mfc-homebrew-$$"
-      mkdir -p "$MFC_WORK_DIR"
-
-      # Function to clean up on exit
-      cleanup() {
-        rm -rf "$MFC_WORK_DIR"
-      }
-      trap cleanup EXIT
-
-      # Create minimal directory structure that mfc.sh expects
-      cd "$MFC_WORK_DIR"
-      ln -sf "#{prefix}/toolchain" toolchain
-      ln -sf "#{libexec}/mfc.sh" mfc.sh
-      ln -sf "#{pkgshare}/examples" examples
+      # Activate the pre-installed venv so all Python dependencies are available
+      # This makes cantera and other packages accessible if users install them in the venv
+      source "#{venv}/bin/activate"
 
-      # Link the venv so mfc.sh doesn't try to create its own
-      mkdir -p build
-      ln -sf "#{libexec}/venv" build/venv
+      # Create a temporary working directory (Cellar is read-only)
+      TMPDIR=$(mktemp -d)
+      trap "rm -rf $TMPDIR" EXIT
 
-      # Set up environment variables
-      export MFC_INSTALL_DIR="#{prefix}"
-      export MFC_BIN_DIR="#{bin}"
-      export BOOST_INCLUDE="#{Formula["boost"].opt_include}"
+      # Copy mfc.sh to temp dir (it may try to write build artifacts)
+      cp "#{libexec}/mfc.sh" "$TMPDIR/"
+      cd "$TMPDIR"
 
       # Run mfc.sh with all arguments
       exec ./mfc.sh "$@"
     EOS
-    chmod 0755, bin/"mfc"
   end
 
   def caveats
     <<~EOS
-      MFC has been installed with:
-        - mfc command-line tool: #{bin}/mfc
-        - pre_process: #{bin}/pre_process
-        - simulation:  #{bin}/simulation
-        - post_process: #{bin}/post_process
+      MFC has been installed successfully!
 
-      Examples are available in:
-        #{pkgshare}/examples
+      To use MFC:
+        mfc --help
+
+      Note: For cases requiring chemical kinetics (Cantera), you'll need to install
+      Cantera separately in the MFC virtual environment:
+
+        source #{libexec}/venv/bin/activate
+        pip install cantera
 
-      To run an example:
-        cd #{pkgshare}/examples/1D_sodshocktube
-        mfc run case.py
+      Alternatively, use conda:
+        conda install -c conda-forge cantera
 
-      Documentation: https://mflowcode.github.io/
+      Examples are available in:
+        #{prefix}/examples
     EOS
   end
 
   test do
-    # Test that the binaries exist and are executable
-    assert_path_exists bin/"mfc"
-    assert_predicate bin/"mfc", :executable?
-    assert_path_exists bin/"pre_process"
-    assert_predicate bin/"pre_process", :executable?
-    assert_path_exists bin/"simulation"
-    assert_predicate bin/"simulation", :executable?
-    assert_path_exists bin/"post_process"
-    assert_predicate bin/"post_process", :executable?
-
-    # Verify toolchain and mfc.sh were installed
-    assert_path_exists libexec/"mfc.sh"
-    assert_path_exists prefix/"toolchain"
-    assert_path_exists prefix/"toolchain/mfc"
-
-    # Verify Python venv was created with dependencies
-    assert_path_exists libexec/"venv"
-    assert_path_exists libexec/"venv/bin/python"
-    assert_path_exists libexec/"venv/bin/pip"
-
-    # Verify examples were installed
-    assert_path_exists pkgshare/"examples"
-    assert_path_exists pkgshare/"examples/1D_sodshocktube/case.py"
-
-    # Test mfc wrapper functionality with pre-installed venv
+    # Test that all binaries exist and are executable
+    %w[pre_process simulation post_process].each do |prog|
+      assert_predicate bin/prog, :exist?
+      assert_predicate bin/prog, :executable?
+    end
+
+    # Test that toolchain is installed
+    assert_predicate prefix/"toolchain", :exist?
+
+    # Test that venv exists and has required packages
+    assert_predicate libexec/"venv", :exist?
+    assert_predicate libexec/"venv/bin/python", :executable?
+
+    # Test that examples exist
+    assert_predicate prefix/"examples", :exist?
+
+    # Test that mfc wrapper works
     system bin/"mfc", "--help"
   end
 end