build(mfem): updated mfem build policy (ensure mfem is build in release mode and with DEBUG off as that can dramatically speed things up)

build-config/mfem/build_policy.hpp.in

@@ -0,0 +1,10 @@
+#pragma once
+// Meson MFEM policy: buildtype=@BUILD_TYPE@, optimization=@OPTIMIZATION@,
+// debug symbols=@DEBUG_SYMBOLS@, NDEBUG=@NDEBUG@.
+// This generated header tracks configuration changes for every MFEM consumer.
+#ifdef __cplusplus
+#include <mfem/config/config.hpp>
+#if defined(MFEM_DEBUG) != @MFEM_DEBUG@
+#error "MFEM_DEBUG does not match the Meson build; rebuild the MFEM bundle."
+#endif
+#endif

build-config/mfem/meson.build

@@ -327,6 +327,12 @@ endif
 system_mfem = disabler()
 system_mfem_dependencies = []
 mfem_provider = 'source bundle'
+# MFEM derives its debug-check macro from CMake's build type, independently
+# of debug symbols. Keep NDEBUG under Meson's existing assertion policy.
+mfem_debug_checks = get_option('buildtype') == 'debug'
+mfem_ndebug = get_option('b_ndebug') == 'true' or (
+  get_option('b_ndebug') == 'if-release' and get_option('buildtype') in ['release', 'plain']
+)
 
 if effective_allow_preinstalled
   system_candidate = dependency(
@@ -416,6 +422,16 @@ if effective_allow_preinstalled
     endif
 
     if system_compatible
+      if not mfem_debug_checks and not cpp.compiles(
+        '#include <mfem/config/config.hpp>\n' +
+        '#ifdef MFEM_DEBUG\n#error MFEM debug checks are enabled\n#endif\n' +
+        'int main(){return 0;}',
+        dependencies: system_candidate_dependencies,
+        name: 'system MFEM has debug checks disabled for this build type',
+      )
+        error('This build type requires MFEM without MFEM_DEBUG. Reconfigure with ' +
+          '-Dallow_preinstalled=false to build a matching MFEM, or select a release MFEM installation.')
+      endif
       system_mfem = system_candidate
       system_mfem_dependencies = system_candidate_dependencies
       mfem_provider = 'system'
@@ -552,6 +568,11 @@ else
     '--cc', cc_executable,
     '--cxx', cxx_executable,
     '--buildtype', get_option('buildtype'),
+    '--optimization', get_option('optimization'),
+    '--debug', get_option('debug') ? 'true' : 'false',
+    '--ndebug', mfem_ndebug ? 'true' : 'false',
+    '--compiler-syntax', cpp.get_argument_syntax(),
+    '--compiler-id', cpp.get_id(),
     '--jobs', get_option('jobs').to_string(),
     '--host-system', host_machine.system(),
     '--cross-build', meson.is_cross_build() ? 'true' : 'false',
@@ -656,6 +677,24 @@ else
   endif
 
   bundle_compile_args = ['-I' + mfem_runtime_prefix / 'include']
+  # The bundle directory is an order-only prerequisite. A configure-time header
+  # also invalidates consumer objects when MFEM's policy changes with otherwise
+  # identical compiler flags (e.g. debug -O2 -> debugoptimized).
+  mfem_policy = configuration_data()
+  mfem_policy.set('BUILD_TYPE', get_option('buildtype'))
+  mfem_policy.set('OPTIMIZATION', get_option('optimization'))
+  mfem_policy.set('DEBUG_SYMBOLS', get_option('debug').to_string())
+  mfem_policy.set('NDEBUG', mfem_ndebug.to_string())
+  mfem_policy.set('MFEM_DEBUG', mfem_debug_checks ? 1 : 0)
+  mfem_policy_header = configure_file(
+    input: 'build_policy.hpp.in', output: 'mfem_build_policy.hpp',
+    configuration: mfem_policy,
+  )
+  if cpp.get_argument_syntax() == 'msvc'
+    bundle_compile_args += ['/FI' + mfem_policy_header.full_path()]
+  else
+    bundle_compile_args += ['-include', mfem_policy_header.full_path()]
+  endif
   bundle_link_args = [
     '-L' + mfem_runtime_prefix / 'lib',
     '-L' + mfem_runtime_prefix / 'lib64',
@@ -760,4 +799,8 @@ if get_option('build_python') and get_option('python_install_native') and not ge
   error('A self-contained Python wheel requires -Dinstall_mfem=true so the native bundle is installed.')
 endif
 
-meson.override_dependency('mfem', mfem_dep)
+# A compatible system dependency is already registered by dependency().
+# Meson rejects overriding that resolved entry. Only register the source bundle.
+if mfem_provider != 'system'
+  meson.override_dependency('mfem', mfem_dep)
+endif