It loads `ext/fiddle/lib/fiddle/version.rb`, which causes constant
redefinition warning:
http://rubyci.s3.amazonaws.com/ubuntu2004/ruby-master/log/20200523T153003Z.log.html.gz
```
[ 6317/20193] TestDefaultGems#test_validate_gemspec/home/chkbuild/chkbuild/tmp/build/20200523T153003Z/ruby/ext/fiddle/lib/fiddle/version.rb:2: warning: already initialized constant Fiddle::VERSION
/home/chkbuild/chkbuild/tmp/build/20200523T153003Z/ruby/.ext/common/fiddle/version.rb:2: warning: previous definition of VERSION was here
= 0.16 s
```
This changeset read the version by manual parsing hack which is also
used in stringio and zlib.
* Allow access to a struct's underlying memory with `struct[offset, length]`.
* Make accessing a struct's underlying memory more convenient.
* refactor memory access unit tests for improved clarity
https://github.com/ruby/fiddle/commit/c082c81bb5
to define HAVE_FFI_CLOSURE_ALLOC.
The macro is used in closure.c, so have_func check is needed.
If pkg-config is not installed, extconf.rb fails to detect the version
of libffi, and does not add "-DUSE_FFI_CLOSURE_ALLOC=1" even when system
libffi version is >= 3.2.
If USE_FFI_CLOSURE_ALLOC is not defined, closure.c attempts to check if
HAVE_FFI_CLOSURE_ALLOC is defined or not, but have_func was removed with
528a3a17977aa1843a26630c96635c3cb161e729, so the macro is always not
defined.
This resulted in this deprecation warning:
https://rubyci.org/logs/rubyci.s3.amazonaws.com/ubuntu2004/ruby-master/log/20200512T123003Z.log.html.gz
```
compiling closure.c
closure.c: In function 'initialize':
closure.c:265:5: warning: 'ffi_prep_closure' is deprecated: use ffi_prep_closure_loc instead [-Wdeprecated-declarations]
265 | result = ffi_prep_closure(pcl, cif, callback, (void *)self);
| ^~~~~~
In file included from ./fiddle.h:42,
from closure.c:1:
/usr/include/x86_64-linux-gnu/ffi.h:334:1: note: declared here
334 | ffi_prep_closure (ffi_closure*,
| ^~~~~~~~~~~~~~~~
```
On OpenBSD, USE_FFI_CLOSURE_ALLOC was always set to 0 previously. In
633a1f15d8228236094ddee12e4e169d655ec49e, the code was modified in a
way that it ended up being set to 1 on OpenBSD. However, that results
in SIGABRT when running make test-all, inside ffi_closure_free.
Setting USE_FFI_CLOSURE_ALLOC back to 0 fixes the issue.
This reverts commit 87f6154bb4c67ca77ee353bb1fe25a922036c0e5.
It turned out that the change fails to build on macOS
https://rubyci.org/logs/rubyci.s3.amazonaws.com/osx1014/ruby-master/log/20200304T074503Z.fail.html.gz
```
+ make 'TESTS=--hide-skip -v fiddle' RUBYOPT=-w test-all
dyld: lazy symbol binding failed: Symbol not found: _ffi_closure_alloc
Referenced from: /Users/hsbt/Documents/cb/tmp/build/20200304T074503Z/ruby/.ext/x86_64-darwin18/fiddle.bundle
Expected in: flat namespace
dyld: Symbol not found: _ffi_closure_alloc
Referenced from: /Users/hsbt/Documents/cb/tmp/build/20200304T074503Z/ruby/.ext/x86_64-darwin18/fiddle.bundle
Expected in: flat namespace
make: *** [yes-test-all] Abort trap: 6
```
This reverts commit efd641ffab34e433a8d8a7d78914576f2425aa90.
This changeset seems to be needed to suppress a warning on Ubuntu 20.04
https://rubyci.org/logs/rubyci.s3.amazonaws.com/ubuntu/ruby-master/log/20200304T033004Z.log.html.gz
```
closure.c:264:5: warning: 'ffi_prep_closure' is deprecated: use ffi_prep_closure_loc instead [-Wdeprecated-declarations]
264 | result = ffi_prep_closure(pcl, cif, callback, (void *)self);
| ^~~~~~
```
I guess there was a reason why the commit was reverted (maybe some CIs
failed?), so try it again.
* Use ffi_closure_free unconditionally.
The current conditionals reflect historic heritage of FFI. Usage of
ffi_closure_free should be better default nowadays, because libffi 3.0.5
fixing issues of ffi_closure_free should be widely available.
* RUBY_LIBFFI_MODVERSION is not used anymore.
Because `ffi_closure_free()` is not used unconditionally, there is no
other use for RUBY_LIBFFI_MODVERSION define, so drop its usage.
* Use more meaningful variable name.
`ver` variable used to be used to pupulate RUBY_LIBFFI_MODVERSION
define. Since the define was removed, the `libffi_dir` variable name
should better describe the remaining usage of the variable.
https://github.com/ruby/fiddle/commit/c49cc79eb8
