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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 for C extensions. 

 How about we just always enable `-Werror=implicit-function-declaration` for all by default? 
 For everything so CRuby and C extensions? 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 link time 
 * never compiles a call in C with the wrong type due to a missing include 
 * avoids issues with compiling CRuby on macOS 

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

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