Issue #17254 has been reported by znz (Kazuhiro NISHIYAMA).

----------------------------------------
Bug #17254: ENV.replace may set nil instead of the proper value
https://bugs.ruby-lang.org/issues/17254

* Author: znz (Kazuhiro NISHIYAMA)
* Status: Open
* Priority: Normal
* ruby -v: ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
On docs.ruby-lang.org, it uses [snap ruby](https://snapcraft.io/ruby), and it failed to run `rdoc`.

```
Oct 07 13:20:08 docs-2020.ruby-lang.org env[6183]: rdoc --title Documentation for Ruby master --main README.md --output /var/www/docs.ruby-lang.org/releases/20200916140300/master -U --all --encoding=UTF-8 .
Oct 07 13:20:08 docs-2020.ruby-lang.org env[6183]: <internal:gem_prelude>:1:in `require': cannot load such file -- rubygems.rb (LoadError)
Oct 07 13:20:08 docs-2020.ruby-lang.org env[6183]:         from <internal:gem_prelude>:1:in `<internal:gem_prelude>'
Oct 07 13:20:08 docs-2020.ruby-lang.org env[6183]: rake aborted!
```

I investigate it, it caused by setting nil instead of the proper value in `ENV.replace`.

```
vagrant@buster:/tmp/t$ cat Gemfile
# frozen_string_literal: true

source "https://rubygems.org"

git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }

# gem "rails"
vagrant@buster:/tmp/t$ env PATH=/var/www/docs.ruby-lang.org/shared/bundle/ruby/2.7.0/bin:/snap/bin:$PATH DEBIAN_DISABLE_RUBYGEMS_INTEGRATION=1 bundle exec env -u RUBYOPT ruby -r/snap/ruby/189/lib/ruby/gems/2.7.0/gems/bundler-2.1.4/lib/bundler/setup -e 'p ENV["RUBYLIB"]'
"/snap/ruby/189/lib/ruby/gems/2.7.0/gems/bundler-2.1.4/lib"
```

Calling `ENV.clear` before `ENV.replace` resolves this issue.

```
vagrant@buster:/tmp/t$ cat /tmp/clear-before-replace.rb
class << ENV
  alias orig_replace replace
  def replace(h)
    clear
    orig_replace(h)
  end
end
vagrant@buster:/tmp/t$ env PATH=/var/www/docs.ruby-lang.org/shared/bundle/ruby/2.7.0/bin:/snap/bin:$PATH DEBIAN_DISABLE_RUBYGEMS_INTEGRATION=1 bundle exec env -u RUBYOPT ruby -r/tmp/clear-before-replace -r/snap/ruby/189/lib/ruby/gems/2.7.0/gems/bundler-2.1.4/lib/bundler/setup -e 'p ENV["RUBYLIB"]'
"/snap/ruby/189/lib/ruby/gems/2.7.0/gems/bundler-2.1.4/lib:/snap/ruby/189/lib/ruby/2.7.0:/snap/ruby/189/lib/ruby/2.7.0/amd64"
```

Where should call `ENV.clear`?
In `ENV.replace` or caller of `ENV.replace`?


---Files--------------------------------
full-env-log.txt (8.96 KB)
rdoc-failed-log.txt (2.57 KB)


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