Issue #21501 has been updated by Eregon (Benoit Daloze). ivoanjo (Ivo Anjo) wrote in #note-6:
I must admit I'm a bit torn on this. As I mentioned above, often the `.c` files are not kept around in the filesystem, whereas in my proposed version I'm showing the exact file (including path) that got loaded into the Ruby VM and that provides the method I'm using.
Actually most `.c` files would be kept around, for user-installed gems with native extensions. But yes for default & bundled gems & core library methods they might not be around. It would still be useful though as e.g. one could easily lookup the source file on GitHub for the corresponding release. Some integration could even automatically show the source, e.g. in the Rails error page or in some editor/IDE.
The small hiccup with this approach for the line `__LINE__` is that it would be the call site for `rb_define_method`, and not where the function itself was defined. TBH I would love to have the actual first line for the function... having it pointing at the `rb_define_method` is a bit less useful?
Ah true, I forgot about that detail. I think it's much better than no line but indeed ideally it would show the line where the function itself is defined but I guess there is no easy way to get that. The `rb_define_method` line is already pretty good though as that will show which C function implements it, and then it's a trivial search to find it (in the 99% cases it's in the same file, and otherwise a search e.g. on the GitHub repository or gem directory would find it). Another advantage is the `.c` file and line would be constant across platforms, and it's clear it's "C extension code". The library name changes per platform e.g. `bigdecimal.so` vs `bigdecimal.bundle`, which can e.g. make googling for a given exception stacktrace more difficult (and doesn't say which language it is but that's pretty minor). ---------------------------------------- Feature #21501: Include native filenames in backtraces as sources for native methods https://bugs.ruby-lang.org/issues/21501#change-113966 * Author: ivoanjo (Ivo Anjo) * Status: Open ---------------------------------------- Consider this example: ```ruby require 'bigdecimal' BigDecimal.singleton_class.prepend( Module.new do def save_rounding_mode super end end ) [:example].each do BigDecimal.save_rounding_mode do puts caller sleep 1 end end ``` which Ruby will print as (from 3.4, since https://bugs.ruby-lang.org/issues/19117): ``` native-filenames-example.rb:6:in 'BigDecimal.save_rounding_mode' native-filenames-example.rb:6:in 'save_rounding_mode' native-filenames-example.rb:12:in 'block in <main>' native-filenames-example.rb:11:in 'Array#each' native-filenames-example.rb:11:in '<main>' ``` Having the class names helps, but I think this behavior can still be confusing. Without looking at the code, and understanding that `Array#each` and `BigDecimal.save_rounding_mode` are written in native code, it can be confusing to see them be assigned to `native-filenames-example.rb` in the backtrace. I would like to propose that, whenever possible (see notes below), Ruby shows the name of the native filename where a method was defined. This would result on the backtrace becoming: ``` /rvm/gems/ruby-3.4.4/gems/bigdecimal-3.2.2/lib/bigdecimal.so:0:in 'BigDecimal.save_rounding_mode' native-filenames-example.rb:6:in 'save_rounding_mode' native-filenames-example.rb:12:in 'block in <main>' /rvm/rubies/ruby-3.4.4/lib/libruby.so.3.4:0:in 'Array#each' native-filenames-example.rb:11:in '<main>' ``` or, alternatively, this mechanism could be applied only to extensions, not to libruby/the ruby binary (it's not particularly hard to detect and exclude it): ``` /rvm/gems/ruby-3.4.4/gems/bigdecimal-3.2.2/lib/bigdecimal.so:0:in 'BigDecimal.save_rounding_mode' native-filenames-example.rb:6:in 'save_rounding_mode' native-filenames-example.rb:12:in 'block in <main>' native-filenames-example.rb:11:in 'Array#each' # Don't touch array ;) native-filenames-example.rb:11:in '<main>' ``` This would make it even easier to understand what's coming from where, and I believe it's a great complement to showing the class names. Furthermore, displaying the actual native libraries matches really well with the semantics we get for regular Ruby files: if I were to look on my machine, I would see `/rvm/gems/ruby-3.4.4/gems/bigdecimal-3.2.2/lib/bigdecimal.so` and `/rvm/rubies/ruby-3.4.4/lib/libruby.so.3.4`. And if I moved them, or overrode them, and loaded them from a different path, I would see the difference. (I say this because in the past I've thought about displaying the actual source .c files and lines, but that a) requires debug information; and b) the files often no longer exist in the filesystem; c) is much harder to implement cross-os). Edit: This also matches with `$LOADED_FEATURES`, which also include the `.so` files as well. --- The extra cool thing is that this is really, really easy to implement! I actually created a [micro gem to show this off](https://github.com/ivoanjo/native-filenames/blob/main/ext/native_filenames_e...) as [well as added this as a feature to the Datadog Ruby profiler](https://github.com/DataDog/dd-trace-rb/pull/4745). Other than checking for headers and whatnot, fetching the info can be implemented in 41 lines of C: https://github.com/ivoanjo/native-filenames/blob/main/ext/native_filenames_e... and works in Linux, macOS and Windows! The way it works is, we can use the function pointer passed to `rb_define_method`, looking it put using `dladdr` (or some of the other variants shown in the code). Then, given just the function pointer, we can get a path back. It's as simple as that -- it can be added transparently as part of storing the cfunc. And if for some reason the path is not available, we could fall back to the current behavior. I'd be very happy to contribute a PR to make this change, but I decided to start with a proposal first as I realize not everyone may be as excited about this idea as I am ;) -- https://bugs.ruby-lang.org/