cmake: detect nettle when building with GnuTLS

`nettle` is a direct dependency of curl, when building with GnuTLS.
Add a new `Find` module to detect it.

Also:
- GHA/macos: drop `nettle` hack no longer necessary.
- add `nettle` to `libcurl.pc`.
- also add `nettle` to `libcurl.pc` in autotools builds.

Follow-up to 781242ffa44a9f9b95b6da5ac5a1bf6372ec6257 #11967
Closes #14285

.github/workflows/macos.yml

@@ -294,8 +294,8 @@ jobs:
             generate: -DCURL_USE_WOLFSSL=ON -DCURL_DISABLE_LDAP=ON -DCURL_DISABLE_LDAPS=ON
             macos-version-min: '10.15'
           - name: 'GnuTLS !ldap'
-            install: gnutls
-            generate: -DCURL_USE_GNUTLS=ON -DCURL_USE_OPENSSL=OFF -DCURL_DISABLE_LDAP=ON -DCURL_DISABLE_LDAPS=ON -DCMAKE_SHARED_LINKER_FLAGS=-L$(brew --prefix nettle)/lib -DCMAKE_EXE_LINKER_FLAGS=-L$(brew --prefix nettle)/lib
+            install: gnutls nettle
+            generate: -DCURL_USE_GNUTLS=ON -DCURL_USE_OPENSSL=OFF -DCURL_DISABLE_LDAP=ON -DCURL_DISABLE_LDAPS=ON
             macos-version-min: '10.15'
         exclude:
           - { compiler: llvm@15, build: { macos-version-min: '10.15' } }

CMake/FindNettle.cmake

@@ -0,0 +1,77 @@
+#***************************************************************************
+#                                  _   _ ____  _
+#  Project                     ___| | | |  _ \| |
+#                             / __| | | | |_) | |
+#                            | (__| |_| |  _ <| |___
+#                             \___|\___/|_| \_\_____|
+#
+# Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+#
+# This software is licensed as described in the file COPYING, which
+# you should have received as part of this distribution. The terms
+# are also available at https://curl.se/docs/copyright.html.
+#
+# You may opt to use, copy, modify, merge, publish, distribute and/or sell
+# copies of the Software, and permit persons to whom the Software is
+# furnished to do so, under the terms of the COPYING file.
+#
+# This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+# KIND, either express or implied.
+#
+# SPDX-License-Identifier: curl
+#
+###########################################################################
+# - Try to find the nettle library
+# Once done this will define
+#
+# NETTLE_FOUND - system has nettle
+# NETTLE_INCLUDE_DIRS - nettle include directories
+# NETTLE_LIBRARIES - nettle library names
+
+if(UNIX)
+  find_package(PkgConfig QUIET)
+  if(PKG_CONFIG_FOUND)
+    pkg_check_modules(NETTLE "nettle")
+  endif()
+endif()
+
+if(NETTLE_FOUND)
+  set(NETTLE_LIBRARIES ${NETTLE_LINK_LIBRARIES})
+else()
+  find_path(NETTLE_INCLUDE_DIR NAMES "nettle/sha2.h")
+  find_library(NETTLE_LIBRARY NAMES "nettle")
+
+  if(NETTLE_INCLUDE_DIR)
+    if(EXISTS "${NETTLE_INCLUDE_DIR}/nettle/version.h")
+      set(_version_regex_major "^#define[ \t]+NETTLE_VERSION_MAJOR[ \t]+([0-9]+).*")
+      set(_version_regex_minor "^#define[ \t]+NETTLE_VERSION_MINOR[ \t]+([0-9]+).*")
+      file(STRINGS "${NETTLE_INCLUDE_DIR}/nettle/version.h"
+        _version_major REGEX "${_version_regex_major}")
+      file(STRINGS "${NETTLE_INCLUDE_DIR}/nettle/version.h"
+        _version_minor REGEX "${_version_regex_minor}")
+      string(REGEX REPLACE "${_version_regex_major}" "\\1" _version_major "${_version_major}")
+      string(REGEX REPLACE "${_version_regex_minor}" "\\1" _version_minor "${_version_minor}")
+      unset(_version_regex_major)
+      unset(_version_regex_minor)
+      set(NETTLE_VERSION "${_version_major}.${_version_minor}")
+      unset(_version_major)
+      unset(_version_minor)
+    else()
+      set(NETTLE_VERSION "0.0")
+    endif()
+  endif()
+
+  include(FindPackageHandleStandardArgs)
+  find_package_handle_standard_args("nettle"
+    REQUIRED_VARS
+      NETTLE_INCLUDE_DIR
+      NETTLE_LIBRARY
+    VERSION_VAR NETTLE_VERSION)
+
+  if(NETTLE_FOUND)
+    set(NETTLE_INCLUDE_DIRS ${NETTLE_INCLUDE_DIR})
+    set(NETTLE_LIBRARIES    ${NETTLE_LIBRARY})
+  endif()
+
+  mark_as_advanced(NETTLE_INCLUDE_DIR NETTLE_LIBRARY)
+endif()

CMakeLists.txt

@@ -541,11 +541,12 @@ endif()
 
 if(CURL_USE_GNUTLS)
   find_package(GnuTLS REQUIRED)
+  find_package(nettle REQUIRED)
   set(SSL_ENABLED ON)
   set(USE_GNUTLS ON)
-  list(APPEND CURL_LIBS ${GNUTLS_LIBRARIES} "nettle")
-  list(APPEND LIBCURL_PC_REQUIRES_PRIVATE "gnutls")
-  include_directories(${GNUTLS_INCLUDE_DIRS})
+  list(APPEND CURL_LIBS ${GNUTLS_LIBRARIES} ${NETTLE_LIBRARIES})
+  list(APPEND LIBCURL_PC_REQUIRES_PRIVATE "gnutls" "nettle")
+  include_directories(${GNUTLS_INCLUDE_DIRS} ${NETTLE_INCLUDE_DIRS})
 
   if(CURL_DEFAULT_SSL_BACKEND AND CURL_DEFAULT_SSL_BACKEND STREQUAL "gnutls")
     set(valid_default_ssl_backend TRUE)

m4/curl-gnutls.m4

@@ -126,7 +126,7 @@ if test "x$OPT_GNUTLS" != xno; then
             AC_MSG_NOTICE([Added $gtlslib to CURL_LIBRARY_PATH])
           fi
         fi
-        LIBCURL_PC_REQUIRES_PRIVATE="$LIBCURL_PC_REQUIRES_PRIVATE gnutls"
+        LIBCURL_PC_REQUIRES_PRIVATE="$LIBCURL_PC_REQUIRES_PRIVATE gnutls nettle"
       fi
 
     fi