meson: add fallback options for eigen/cppad

meson.build

@@ -3,15 +3,37 @@ project('usadelndsoc', ['cpp', 'fortran'],
         meson_version: '>= 0.55.0',
         default_options : ['cpp_std=c++17', 'build.cpp_std=c++17'])
 
+cpp = meson.get_compiler('cpp')
+
 cppad_dep = dependency('cppad')
 eigen3_dep = dependency('eigen3')
 
+if not cppad_dep.found()
+  cppad_dep = cpp.find_library('libcppad_lib',
+                               dirs : [get_option('cppad_lib')],
+                               has_headers : ['cppad/cppad.h'],
+                               header_include_directories : [get_option('cppad_inc')])
+  if not cppad_dep.found()
+    cppad_dep = cpp.find_library('cppad_lib',
+                                 dirs : [get_option('cppad_lib')],
+                                 has_headers : ['cppad/cppad.h'],
+                                 header_include_directories : [get_option('cppad_inc')],
+                                 required : true)
+  endif
+endif
+
+if not eigen3_dep.found()
+  if cpp.has_header('Eigen/Core', include_directories : [get_option('eigen_lib')])
+    eigen3_dep = declare_dependency(include_directories : [get_option('eigen_lib')])
+  else
+    error('Eigen/Core header not found')
+  endif
+endif
+
 py_mod = import('python')
 py3 = py_mod.find_installation('python3')
 py3_dep = py3.dependency()
 
-cpp = meson.get_compiler('cpp')
-
 incdir_numpy = run_command(py3,
   [
     '-c',

meson_options.txt

+option('cppad_inc',
+       type: 'string')
+option('cppad_lib',
+       type: 'string')
+option('eigen_inc',
+       type: 'string')