Feature #18615
Updated by Eregon (Benoit Daloze) over 2 years ago
Currently, if a C extension refers a non-existing function it will continue to compile and only emit a warning.
And compilation warnings are hidden by default for both `gem install` and `bundle install` (`gem install -V somegem` shows them).
A concrete example is the sqlite3 gem, if we use version 1.3.13 it fails only at runtime:
```
$ gem install sqlite3:1.3.13
Fetching sqlite3-1.3.13.gem
Building native extensions. This could take a while...
Successfully installed sqlite3-1.3.13
1 gem installed
$ ruby -rsqlite3 -e 'db = SQLite3::Database.new "test.db"; p db'
ruby: symbol lookup error: /home/eregon/.rubies/ruby-3.0.2/lib/ruby/gems/3.0.0/gems/sqlite3-1.3.13/lib/sqlite3/sqlite3_native.so: undefined symbol: rb_check_safe_obj
```
This is not nice, it should have failed clearly at compile time, saying the function does not exist.
There is a compiler warning, which can only be seen with (and so most users would miss it):
```
$ gem install -V sqlite3:1.3.13
...
database.c: In function ‘initialize’:
database.c:60:3: warning: implicit declaration of function ‘rb_check_safe_obj’; did you mean ‘rb_check_safe_str’? [-Wimplicit-function-declaration]
60 | rb_check_safe_obj(file);
| ^~~~~~~~~~~~~~~~~
| rb_check_safe_str
...
```
Also multiple CRuby releases are broken on macOS which seems to enable `-Werror=implicit-function-declaration` by default (e.g., #17777).
EDIT: `-Werror=implicit-function-declaration` is now default for building CRuby, but not for C extensions.
How about we just always enable `-Werror=implicit-function-declaration` for all C extensions? (builtin or not).
It:
* shows clear errors early on and shows where the missing function is called (explained just above), instead of delaying them to runtime link time
* never compiles a call in C with the wrong type due to a missing include
From https://github.com/oracle/truffleruby/issues/2618