Issue #17254 has been updated by jeremyevans0 (Jeremy Evans).


Looking at the `ENV.replace` implementation, the reason it doesn't call `clear` is it isn't thread-safe.  `ENV.replace` tries to set all ENV keys in the replacement hash (the argument), then remove keys for ENV that aren't in the replacement hash.  This ensures that at no point does the environment have a missing key if ENV already has the key and the replacement hash also has the key.

So having `ENV.replace` call `ENV.clear` is not good as it would break thread safety.  It sounds like a bug in `ENV.replace` if it is actually setting an environment key to a nil value.  I couldn't recreate the error by doing:

```ruby
ENV.clear
ENV.replace(ENV_VALUE_FROM_YOUR_EXAMPLE)
ENV.replace(h_VALUE_FROM_YOUR_EXAMPLE)
```

One thing I noted is the ENV in your example before the replace has multiple entries for "GEM_HOME", "GEM_PATH", and "RUBYLIB".  That seems like a bug itself, and it is possibly related to the cause of `ENV.replace` resulting in a `nil` ENV value.  Possibly the issue is due to multiple ENV keys with the same content but different encodings?

----------------------------------------
Bug #17254: ENV.replace may set nil instead of the proper value
https://bugs.ruby-lang.org/issues/17254#change-88028

* 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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