From: "shyouhei (Shyouhei Urabe)" <noreply@...>
Date: 2022-03-10T02:02:37+00:00
Subject: [ruby-core:107809] [Ruby master Feature#18615] Use -Werror=implicit-function-declaration by default for building C extensions

Issue #18615 has been updated by shyouhei (Shyouhei Urabe).


There is nothing that a Ruby _user_ can do for this situation.  Gem _authors_ should be aware of their bugs.  Hiding compiler warnings from their eyes is the problem.  `bundle install` is irrelevant here.  I'm not against bundler to remain silent.

----------------------------------------
Feature #18615: Use -Werror=implicit-function-declaration by default for building C extensions
https://bugs.ruby-lang.org/issues/18615#change-96737

* Author: Eregon (Benoit Daloze)
* Status: Open
* Priority: Normal
----------------------------------------
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
* never compiles a call in C with the wrong type due to a missing include

From https://github.com/oracle/truffleruby/issues/2618



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