build/pkgs/python3/spkg-configure.m4: Do not check sysconfig CPPFLAGS so that /usr/bin/python3 is accepted on macOS; reject broken homebrew python3 unless requested explicitly with configgure --with-python=...

Author: Matthias Koeppe

build/pkgs/python3/spkg-configure.m4

@@ -29,6 +29,9 @@ SAGE_SPKG_CONFIGURE([python3], [
            SAGE_CHECK_PYTHON_FOR_VENV([$ac_path_PYTHON3],
                                            MIN_VERSION, LT_VERSION,
                                            $check_modules, [
+                    AS_IF([[conftest_venv/bin/python3 -m sysconfig | grep '^\sw*\(C\|LD\)FLAGS *=.*[" ]-[IL]' ]] [>& AS_MESSAGE_LOG_FD 2>&1 ], [
+                        AC_MSG_WARN([this is a misconfigured Python whose sysconfig compiler/linker flags contain -I or -L options, which may cause wrong versions of libraries to leak into the build of Python packages - see https://trac.sagemath.org/ticket/31132])
+                    ])
                     dnl It is good
                     ac_cv_path_PYTHON3="$ac_path_PYTHON3"
                     ac_path_PYTHON3_found=:
@@ -45,17 +48,24 @@ SAGE_SPKG_CONFIGURE([python3], [
                 SAGE_CHECK_PYTHON_FOR_VENV([$ac_path_PYTHON3],
                                            MIN_VERSION, LT_VERSION,
                                            $check_modules, [
-                    dnl It is good
-                    ac_cv_path_PYTHON3="$ac_path_PYTHON3"
-                    ac_path_PYTHON3_found=:
-                    AC_MSG_RESULT([yes])
-                    dnl introduction for AC_MSG_RESULT printed by AC_CACHE_CHECK
-                    AC_MSG_CHECKING([for python3 >= ]MIN_VERSION[, < ]LT_VERSION[ with modules $check_modules])
+                    AS_IF([[conftest_venv/bin/python3 -m sysconfig | grep '^\sw*\(C\|LD\)FLAGS *=.*[" ]-[IL]' ]] [>& AS_MESSAGE_LOG_FD 2>&1 ], [
+                        AC_MSG_RESULT([no, this is a misconfigured Python whose sysconfig compiler/linker flags contain -I or -L options, which may cause wrong versions of libraries to leak into the build of Python packages - see https://trac.sagemath.org/ticket/31132; to use it anyway, use ./configure --with-python=$ac_path_PYTHON3])
+                    ], [
+                        dnl It is good
+                        ac_cv_path_PYTHON3="$ac_path_PYTHON3"
+                        ac_path_PYTHON3_found=:
+                        AC_MSG_RESULT([yes])
+                        dnl introduction for AC_MSG_RESULT printed by AC_CACHE_CHECK
+                        AC_MSG_CHECKING([for python3 >= ]MIN_VERSION[, < ]LT_VERSION[ with modules $check_modules])
+                    ])
                 ])
             ])
 	])
       ])
-      AS_IF([test -z "$ac_cv_path_PYTHON3"], [sage_spkg_install_python3=yes])
+      AS_IF([test -z "$ac_cv_path_PYTHON3"], [
+          AC_MSG_NOTICE([to try to use a different system python, use ./configure --with-python=/path/to/python])
+          sage_spkg_install_python3=yes
+      ])
       m4_popdef([MIN_VERSION])
       m4_popdef([LT_VERSION])
     ])

m4/sage_check_python_for_venv.m4

@@ -108,9 +108,6 @@ setup(name="config_check_distutils_cxx", ext_modules=modules)
 exit(0)
 EOF
                                     AS_IF([CC="$CC" CXX="$CXX" conftest_venv/bin/python3 conftest.py --verbose build --build-base=conftest.dir >& AS_MESSAGE_LOG_FD 2>&1 ], [
-                                        AS_IF([[conftest_venv/bin/python3 -m sysconfig | grep '^\sw*\(C[PX]*\|LD\)FLAGS *=.*[" ]-[IL]' ]] [>& AS_MESSAGE_LOG_FD 2>&1 ], [
-                                            AC_MSG_WARN([this is a misconfigured Python whose sysconfig compiler/linker flags contain -I or -L options, which may cause wrong versions of libraries to leak into the build of Python packages - see https://trac.sagemath.org/ticket/31132])
-                                        ])
                                         COMMANDS_IF_GOOD], [
                                         AC_MSG_RESULT([no, the version is in the supported range, and the modules can be imported, but distutils cannot build a C++ 11 extension])
                                     ])