Improve options for linking with OpenSSL especially on MacOS (brianma…

…rio#1303)

Starting a few MacOS majors ago, OpenSSL was no longer included in a way that
applications could link against. Even the system Ruby at /usr/bin/ruby was
modified to use a MacOS internal SSL implementation.

The most common workaround is to use Homebrew to install OpenSSL. Using GitHub
Actions as the project's CI tool, we found that both [email protected] and openssl@3
were installed in the default image, and that openssl@3 was returned by default
but this mismatched the version the MySQL client libraries were compiled against.

While the quick workaround might be to look for [email protected] instead of openssl,
a more general improvement is to provide an option for users to specify where
OpenSSL is installed. Indeed this issue has been the cause of many postings on
GH issues and Stack Overflow over the years. Hopefully this PR improves the
situation for a broad swath of users!

Unlike the existing option `--with-opt-dir`, the new option `--with-openssl-dir`
will fail if the argument is not a valid path rather than producing unexpected
results at runtime.

This is the default behavior on MacOS:

    --with-openssl-dir=$(brew --prefix openssl)

If you have both [email protected] and openssl@3 installed, be explicit:

    --with-openssl-dir=$(brew --prefix [email protected])

The option is available on all platforms and may be helpful for non-default
OpenSSL installations on Linux or FreeBSD as well.

Co-authored-by: Jun Aruga <[email protected]>
(cherry picked from commit a89fd5b)

ext/mysql2/extconf.rb

@@ -2,6 +2,8 @@
 require 'mkmf'
 require 'English'
 
+### Some helper functions
+
 def asplode(lib)
   if RUBY_PLATFORM =~ /mingw|mswin/
     abort "-----\n#{lib} is missing. Check your installation of MySQL or Connector/C, and try again.\n-----"
@@ -22,6 +24,8 @@ def add_ssl_defines(header)
   $CFLAGS << ' -DNO_SSL_MODE_SUPPORT' if has_no_support
 end
 
+### Check for Ruby C extention interfaces
+
 # 2.1+
 have_func('rb_absint_size')
 have_func('rb_absint_singlebit_p')
@@ -36,6 +40,31 @@ def add_ssl_defines(header)
 have_func('rb_intern3')
 have_func('rb_big_cmp')
 
+### Find OpenSSL library
+
+# User-specified OpenSSL if explicitly specified
+if with_config('openssl-dir')
+  _, lib = dir_config('openssl')
+  if lib
+    # Ruby versions below 2.0 on Unix and below 2.1 on Windows
+    # do not properly search for lib directories, and must be corrected:
+    # https://bugs.ruby-lang.org/projects/ruby-trunk/repository/revisions/39717
+    unless lib && lib[-3, 3] == 'lib'
+      @libdir_basename = 'lib'
+      _, lib = dir_config('openssl')
+    end
+    abort "-----\nCannot find library dir(s) #{lib}\n-----" unless lib && lib.split(File::PATH_SEPARATOR).any? { |dir| File.directory?(dir) }
+    warn "-----\nUsing --with-openssl-dir=#{File.dirname lib}\n-----"
+    $LDFLAGS << " -L#{lib}"
+  end
+# Homebrew OpenSSL on MacOS
+elsif RUBY_PLATFORM =~ /darwin/ && system('command -v brew')
+  openssl_location = `brew --prefix openssl`.strip
+  $LDFLAGS << " -L#{openssl_location}/lib" if openssl_location
+end
+
+### Find MySQL client library
+
 # borrowed from mysqlplus
 # http://github.com/oldmoe/mysqlplus/blob/master/ext/extconf.rb
 dirs = ENV.fetch('PATH').split(File::PATH_SEPARATOR) + %w(
@@ -116,10 +145,13 @@ def add_ssl_defines(header)
 have_struct_member('MYSQL', 'net.pvio', mysql_h)
 have_const('MYSQL_ENABLE_CLEARTEXT_PLUGIN', mysql_h)
 
+### Compiler flags to help catch errors
+
 # This is our wishlist. We use whichever flags work on the host.
 # -Wall and -Wextra are included by default.
 wishlist = [
   '-Weverything',
+  '-Wno-compound-token-split-by-macro', # Fixed in Ruby 2.7+ at https://bugs.ruby-lang.org/issues/17865
   '-Wno-bad-function-cast', # rb_thread_call_without_gvl returns void * that we cast to VALUE
   '-Wno-conditional-uninitialized', # false positive in client.c
   '-Wno-covered-switch-default', # result.c -- enum_field_types (when fully covered, e.g. mysql 5.5)
@@ -144,6 +176,8 @@ def add_ssl_defines(header)
 
 $CFLAGS << ' ' << usable_flags.join(' ')
 
+### Sanitizers to help with debugging -- many are available on both Clang/LLVM and GCC
+
 enabled_sanitizers = disabled_sanitizers = []
 # Specify a commna-separated list of sanitizers, or try them all by default
 sanitizers = with_config('sanitize')
@@ -178,6 +212,8 @@ def add_ssl_defines(header)
   $CFLAGS << ' -g -fno-omit-frame-pointer'
 end
 
+### Find MySQL Client on Windows, set RPATH to find the library at runtime
+
 if RUBY_PLATFORM =~ /mswin|mingw/
   # Build libmysql.a interface link library
   require 'rake'