Since around 2018, we have been using spaces for indentation for newly
added code[1]. The mixed use of tabs and spaces has repeatedly confused
new contributors who configured their editors to use a different tab
size than 8. Since git blame can now skip specific commits, ruby/ruby
did a mass reformatting of tabs in 2022[2]. Do the same in ruby/openssl.

While at it, fix a few indentation issues, mainly in switch-case labels
and in ossl_ssl_session.c, which used doubled indentation size.

This patch contains white-space changes only. git diff -w output should
be empty.

[1] https://bugs.ruby-lang.org/issues/14246
[2] https://bugs.ruby-lang.org/issues/18891

https://github.com/ruby/openssl/commit/4d6214f507

These declarations were added to every source file because older
versions of RDoc did not resolve ancestor tree across files. Since
RDoc 6.9.0 supports this, this workaround is no longer needed.

    https://redirect.github.com/ruby/rdoc/pull/1217

https://github.com/ruby/openssl/commit/6491ce63be

Remove the following subclasses of OpenSSL::PKey::PKeyError and make
them aliases of it.

 - OpenSSL::PKey::DHError
 - OpenSSL::PKey::DSAError
 - OpenSSL::PKey::ECError
 - OpenSSL::PKey::RSAError

Historically, methods defined on OpenSSL::PKey and OpenSSL::PKey::PKey
raise OpenSSL::PKey::PKeyError, while methods on the subclasses raise
their respective exception classes. However, this distinction is not
particularly useful since all those exception classes represent the
same kind of errors from the underlying EVP_PKEY API.

I think this convention comes from the fact that OpenSSL::PKey::{DH,
DSA,RSA} originally wrapped the corresponding OpenSSL structs DH, DSA,
and RSA, before they were unified to wrap EVP_PKEY, way back in 2002.

OpenSSL::PKey::EC::Group::Error and OpenSSL::PKey::EC::Point::Error
are out of scope of this change, as they are not subclasses of
OpenSSL::PKey::PKeyError and do not represent errors from the EVP_PKEY
API.

https://github.com/ruby/openssl/commit/e74ff3e272

In OpenSSL <= 1.1.1, EVP_PKEY_get0() always returned a valid object, so
a NULL check was not necessary. In OpenSSL 3.0, the function can return
NULL (https://docs.openssl.org/3.0/man7/migration_guide/#deprecated-function-mappings),
so guard against this issue.

https://github.com/ruby/openssl/commit/dc90b9c51e

Raise ArgumentError if this is attempted when the extension is compiled
with OpenSSL 3.0 or later. The form will be fully removed when we drop
support for OpenSSL 1.1.1.

When OpenSSL::PKey::{DH,DSA,EC,RSA}.new is called without any arguments,
it sets up an empty corresponding low-level struct and wraps it in an
EVP_PKEY. This is useful when the user later fills the missing fields
using low-level setter methods such as OpenSSL::PKey::RSA#set_key.

Such setter methods are not compatible with OpenSSL 3.0 or later, where
EVP_PKEY is immutable once created. This means that the ability to
create an empty instance is useless.

https://github.com/ruby/openssl/commit/affd569f78

https://github.com/ruby/openssl/commit/17f87d2cf0

Move the definitions to lib/openssl/pkey.rb. They need not to be in the
extension and can be implemented using existing methods.

This reduces direct usage of the now-deprecated OpenSSL APIs around the
low-level structs such as DH, DSA, or RSA.

https://github.com/ruby/openssl/commit/c14178f387

https://github.com/ruby/openssl/commit/85d6b7f192

Update the references to the file "LICENCE" with "COPYING".

The file LICENCE doesn't exist in ruby/ruby nor ruby/openssl. This has
been always the case since OpenSSL for Ruby 2 was merged to the ruby
tree as a standard library in 2003.

In OpenSSL for Ruby 2's CVS repository[1], the LICENCE file contained
an old version of the Ruby License, identical to the COPYING file that
was in Ruby's tree at that time (r4128[2]).

[1] http://cvs.savannah.gnu.org/viewvc/rubypki/ossl2/LICENCE?revision=1.1.1.1&view=markup
[2] https://github.com/ruby/ruby/blob/231247c010acba191b78ed2d1310c935e63ad919/COPYING

https://github.com/ruby/openssl/commit/5bccf07d04

Describe the behavior of OpenSSL::PKey::{DH,DSA,EC,RSA}#to_pem
and #to_der more clearly. They return a different result depending on
whether the pkey is a public or private key. This was not documented
adequately.

Also, suggest the use of OpenSSL::PKey::PKey#private_to_pem
and #public_to_pem instead, if possible.

https://github.com/ruby/openssl/commit/d22769af8f