[PATCH] md5, sha1, sha256, sha512:: support --with-openssl=auto_gpl_compat

[Pádraig Brady]

* m4/gl-openssl.m4: Add a new "auto_gpl_compat" mode,
which will auto enable use of openssl, only for >= version 3,
which is newly licensed under the Apache Software License.
This will be used from coreutils for example by adding
gl_SET_CRYPTO_CHECK_DEFAULT([auto_gpl_compat]) to configure.ac.
Even though "auto_gpl_compat" is less aggressive than "auto",
we leave the default at "no" so projects can opt in to the
extra dependency.
---
 ChangeLog        |  7 +++++++
 m4/gl-openssl.m4 | 32 +++++++++++++++++++++++++-------
 2 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index ac61fdf..740a982 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2020-01-01  Pádraig Brady  <address@hidden>
+
+       md5, sha1, sha256, sha512:: support --with-openssl=auto_gpl_compat
+       * m4/gl-openssl.m4: Add a new "auto_gpl_compat" mode,
+       which will auto enable use of openssl, only for >= version 3,
+       which is newly licensed under the Apache Software License.
+
 2020-01-01  Bruno Haible  <address@hidden>
 
        doc: Update documentation about wchar_t.
diff --git a/m4/gl-openssl.m4 b/m4/gl-openssl.m4
index 0195202..d2d1d6f 100644
--- a/m4/gl-openssl.m4
+++ b/m4/gl-openssl.m4
@@ -1,4 +1,4 @@
-# gl-openssl.m4 serial 3
+# gl-openssl.m4 serial 4
 dnl Copyright (C) 2013-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -21,7 +21,9 @@ AC_DEFUN([gl_CRYPTO_CHECK],
   AC_ARG_WITH([openssl],
     [AS_HELP_STRING([--with-openssl],
       [use libcrypto hash routines. Valid ARGs are:
-       'yes', 'no', 'auto' => use if available,
+       'yes', 'no',
+       'auto' => use if any version available,
+       'auto_gpl_compat' => use if gpl compatible version available,
        'optional' => use if available and warn if not available;
        default is ']gl_CRYPTO_CHECK_DEFAULT['.
        Note also --with-linux-crypto, which will enable
@@ -37,11 +39,27 @@ AC_DEFUN([gl_CRYPTO_CHECK],
 
   AC_SUBST([LIB_CRYPTO])
   if test "x$with_openssl" != xno; then
-    AC_CHECK_LIB([crypto], [$1],
-      [AC_CHECK_HEADERS([openssl/$ALG_header],
-         [LIB_CRYPTO=-lcrypto
-          AC_DEFINE([HAVE_OPENSSL_$1], [1],
-            [Define to 1 if libcrypto is used for $1.])])])
+    if test "x$with_openssl" = xauto_gpl_compat; then
+      AC_CACHE_CHECK([whether openssl is GPL compatible],
+                     [gl_cv_openssl_gpl_compat],
+        [AC_COMPILE_IFELSE(
+           [AC_LANG_PROGRAM([[
+                #include <openssl/opensslv.h>
+                #if OPENSSL_VERSION_MAJOR < 3
+                  #error "openssl >= version 3 not found"
+                #endif
+              ]])],
+           [gl_cv_openssl_gpl_compat=yes],
+           [gl_cv_openssl_gpl_compat=no])])
+    fi
+    if test "x$with_openssl" != xauto_gpl_compat ||
+       test "x$gl_cv_openssl_gpl_compat" = xyes; then
+      AC_CHECK_LIB([crypto], [$1],
+        [AC_CHECK_HEADERS([openssl/$ALG_header],
+           [LIB_CRYPTO=-lcrypto
+            AC_DEFINE([HAVE_OPENSSL_$1], [1],
+              [Define to 1 if libcrypto is used for $1.])])])
+    fi
     if test "x$LIB_CRYPTO" = x; then
       if test "x$with_openssl" = xyes; then
         AC_MSG_ERROR([openssl development library not found for $1])
-- 
2.9.3