bpo-45723: Add helpers for save/restore env

PoC: Apply to SQLite check.

Author: Erlend E. Aasland

configure

@@ -2806,6 +2806,7 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
+
 if test "$srcdir" != . -a "$srcdir" != "$(pwd)"; then
     # If we're building out-of-tree, we need to make sure the following
     # resources get picked up before their $srcdir counterparts.
@@ -11022,16 +11023,17 @@ fi
 as_fn_append LIBSQLITE3_CFLAGS ' -I$(srcdir)/Modules/_sqlite'
 
 save_CFLAGS=$CFLAGS
-save_CPPFLAGS=$CPPFLAGS
-save_LDFLAGS=$LDFLAGS
-save_LIBS=$LIBS
-CPPFLAGS="$LIBSQLITE3_CFLAGS $CFLAGS"
-LDFLAGS="$LIBSQLITE3_LIBS $LDFLAGS"
+  save_CPPFLAGS=$CPPFLAGS
+  save_LDFLAGS=$LDFLAGS
+  save_LIBS=$LIBS
+
+  CPPFLAGS="$LIBSQLITE3_CFLAGS $CFLAGS"
+  LDFLAGS="$LIBSQLITE3_LIBS $LDFLAGS"
 
-ac_fn_c_check_header_mongrel "$LINENO" "sqlite3.h" "ac_cv_header_sqlite3_h" "$ac_includes_default"
+  ac_fn_c_check_header_mongrel "$LINENO" "sqlite3.h" "ac_cv_header_sqlite3_h" "$ac_includes_default"
 if test "x$ac_cv_header_sqlite3_h" = xyes; then :
 
-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for sqlite3_open_v2 in -lsqlite3" >&5
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking for sqlite3_open_v2 in -lsqlite3" >&5
 $as_echo_n "checking for sqlite3_open_v2 in -lsqlite3... " >&6; }
 if ${ac_cv_lib_sqlite3_sqlite3_open_v2+:} false; then :
   $as_echo_n "(cached) " >&6
@@ -11069,15 +11071,15 @@ fi
 $as_echo "$ac_cv_lib_sqlite3_sqlite3_open_v2" >&6; }
 if test "x$ac_cv_lib_sqlite3_sqlite3_open_v2" = xyes; then :
 
-    have_sqlite3=yes
-    cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+      have_sqlite3=yes
+      cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
 
-        #include <sqlite3.h>
-        #if SQLITE_VERSION_NUMBER < 3007015
-        #  error "SQLite 3.7.15 or higher required"
-        #endif
+          #include <sqlite3.h>
+          #if SQLITE_VERSION_NUMBER < 3007015
+          #  error "SQLite 3.7.15 or higher required"
+          #endif
 
 int
 main ()
@@ -11099,7 +11101,7 @@ else
   have_sqlite3=no
 fi
 
-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for sqlite3_load_extension in -lsqlite3" >&5
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking for sqlite3_load_extension in -lsqlite3" >&5
 $as_echo_n "checking for sqlite3_load_extension in -lsqlite3... " >&6; }
 if ${ac_cv_lib_sqlite3_sqlite3_load_extension+:} false; then :
   $as_echo_n "(cached) " >&6
@@ -11149,10 +11151,12 @@ fi
 
 
 
-CFLAGS=$save_CFLAGS
-CPPFLAGS=$save_CPPFLAGS
-LDFLAGS=$save_LDFLAGS
-LIBS=$save_LIBS
+  CFLAGS=$save_CFLAGS
+  CPPFLAGS=$save_CPPFLAGS
+  LDFLAGS=$save_LDFLAGS
+  LIBS=$save_LIBS
+
+
 
 # Check for support for loadable sqlite extensions
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for --enable-loadable-sqlite-extensions" >&5

configure.ac

@@ -23,6 +23,32 @@ m4_ifdef(
     [AC_MSG_ERROR([Please install pkgconf's m4 macro package and re-run autoreconf])]
 )dnl
 
+dnl Helpers for saving and restoring environment variables:
+dnl - _SAVE_VAR([VAR])         Helper for SAVE_ENV; stores VAR as save_VAR
+dnl - _RESTORE_VAR([VAR])      Helper for RESTORE_ENV; restores VAR from save_VAR
+dnl - SAVE_ENV                 Saves CFLAGS, LDFLAGS, LIBS, and CPPFLAGS
+dnl - RESTORE_ENV              Restores CFLAGS, LDFLAGS, LIBS, and CPPFLAGS
+dnl - WITH_SAVE_ENV([SCRIPT])  Runs SCRIPT wrapped with SAVE_ENV/RESTORE_ENV
+AC_DEFUN([_SAVE_VAR], [AS_VAR_COPY([save_][$1], [$1])])dnl
+AC_DEFUN([_RESTORE_VAR], [AS_VAR_COPY([$1], [save_][$1])])dnl
+AC_DEFUN([SAVE_ENV],
+  [_SAVE_VAR([CFLAGS])]
+  [_SAVE_VAR([CPPFLAGS])]
+  [_SAVE_VAR([LDFLAGS])]
+  [_SAVE_VAR([LIBS])]
+)dnl
+AC_DEFUN([RESTORE_ENV],
+  [_RESTORE_VAR([CFLAGS])]
+  [_RESTORE_VAR([CPPFLAGS])]
+  [_RESTORE_VAR([LDFLAGS])]
+  [_RESTORE_VAR([LIBS])]
+)dnl
+AC_DEFUN([WITH_SAVE_ENV],
+  [SAVE_ENV]
+  [$1]
+  [RESTORE_ENV]
+)dnl
+
 AC_SUBST(BASECPPFLAGS)
 if test "$srcdir" != . -a "$srcdir" != "$(pwd)"; then
     # If we're building out-of-tree, we need to make sure the following
@@ -3175,34 +3201,26 @@ PKG_CHECK_MODULES(
 AS_VAR_APPEND([LIBSQLITE3_CFLAGS], [' -I$(srcdir)/Modules/_sqlite'])
 
 dnl bpo-45774/GH-29507: The CPP check in AC_CHECK_HEADER can fail on FreeBSD,
-dnl hence CPPFLAGS instead of CFLAGS. We still need to save CFLAGS, because it
-dnl is touched by AC_CHECK_HEADER.
-AS_VAR_COPY([save_CFLAGS], [CFLAGS])
-AS_VAR_COPY([save_CPPFLAGS], [CPPFLAGS])
-AS_VAR_COPY([save_LDFLAGS], [LDFLAGS])
-AS_VAR_COPY([save_LIBS], [LIBS])
-CPPFLAGS="$LIBSQLITE3_CFLAGS $CFLAGS"
-LDFLAGS="$LIBSQLITE3_LIBS $LDFLAGS"
-
-AC_CHECK_HEADER([sqlite3.h], [
-  AC_CHECK_LIB([sqlite3], [sqlite3_open_v2], [
-    have_sqlite3=yes
-    AC_COMPILE_IFELSE([
-      AC_LANG_PROGRAM([
-        #include <sqlite3.h>
-        #if SQLITE_VERSION_NUMBER < 3007015
-        #  error "SQLite 3.7.15 or higher required"
-        #endif
-      ], [])
-    ], [have_supported_sqlite3=yes], [have_supported_sqlite3=no])
-  ], [have_sqlite3=no])
-  AC_CHECK_LIB([sqlite3], [sqlite3_load_extension])
-])
-
-AS_VAR_COPY([CFLAGS], [save_CFLAGS])
-AS_VAR_COPY([CPPFLAGS], [save_CPPFLAGS])
-AS_VAR_COPY([LDFLAGS], [save_LDFLAGS])
-AS_VAR_COPY([LIBS], [save_LIBS])
+dnl hence CPPFLAGS instead of CFLAGS.
+WITH_SAVE_ENV(
+  CPPFLAGS="$LIBSQLITE3_CFLAGS $CFLAGS"
+  LDFLAGS="$LIBSQLITE3_LIBS $LDFLAGS"
+
+  AC_CHECK_HEADER([sqlite3.h], [
+    AC_CHECK_LIB([sqlite3], [sqlite3_open_v2], [
+      have_sqlite3=yes
+      AC_COMPILE_IFELSE([
+        AC_LANG_PROGRAM([
+          #include <sqlite3.h>
+          #if SQLITE_VERSION_NUMBER < 3007015
+          #  error "SQLite 3.7.15 or higher required"
+          #endif
+        ], [])
+      ], [have_supported_sqlite3=yes], [have_supported_sqlite3=no])
+    ], [have_sqlite3=no])
+    AC_CHECK_LIB([sqlite3], [sqlite3_load_extension])
+  ])
+)
 
 # Check for support for loadable sqlite extensions
 AC_MSG_CHECKING(for --enable-loadable-sqlite-extensions)