[ruby-core:97646] [Ruby master Feature#16744] Flag to load current bundle without using bundle exec

Issue #16744 has been updated by headius (Charles Nutter).


> Given that latest Bundler no longer creates a subprocess for bundle exec

Your example is incorrect. `exec` reuses process ID.

```
$ jruby -e 'puts $$; exec %{jruby -e "puts $$"}'
85727
85727
```

----------------------------------------
Feature #16744: Flag to load current bundle without using bundle exec
https://bugs.ruby-lang.org/issues/16744#change-84845

* Author: headius (Charles Nutter)
* Status: Open
* Priority: Normal
----------------------------------------
The `bundle exec` command is used by Ruby users primarily to start up a Ruby command or application with only its specific locked dependencies wired up. Unfortunately to do this it currently double-launches, executing a second Ruby command and doubling the base startup time for these use cases. With Bundler becoming part of the standard library, it seems a good time to add support for doing what `bundle exec` does without requiring a relaunch.

For many years, JRuby has implemented the `-G`/`--gemfile` flag which requires in `bundler/setup` before user code starts, eliminating the need to bundle exec in these situations.

https://github.com/jruby/jruby/commit/ea0eed02b4eb57c2198afa9fd47f94bc46cfc69f

This is based on the same flags in Rubinius:

https://github.com/rubinius/rubinius/commit/edc94f2e3a61d8c94031a942b2024c6c5aa3ea94

There's at least one more commit later on in Rubinius that fixes some interations between `-G` and `-S`.

Obviously this does not eliminate `bundle exec` use cases where the target command is not a Ruby command, but that is a very specific (and rather strange to me) feature. The majority of use cases are booting up a Ruby command, for which this implementation of `-G` would be sufficient (I think). 

There may be different or additional ways that `bundle exec` attempts to isolate the subcommand's environment and dependencies, but I believe requiring `bundler/setup` at boot comes pretty close.

See also this bug report where I suggest using JRuby's embedding APIs to do `bundle exec`. We very much want to help eliminate this double-launching, one way or another.

https://github.com/rubygems/rubygems/issues/3246



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