[ruby-core:112963] [Ruby master Bug#19403] Unable to Build Native Gems on Mac with Ruby 3.1.0+

Issue #19403 has been updated by nagachika (Tomoyuki Chikanaga).

Backport changed from 2.7: DONTNEED, 3.0: DONTNEED, 3.1: REQUIRED, 3.2: DONE to 2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONE, 3.2: DONE

ruby_3_1 485e0e46a58ff1a28eecd63b804b3dbea4b95b98 merged revision(s) 3a7367ccc319499127ead147e5a08f769e44208e.

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Bug #19403: Unable to Build Native Gems on Mac with Ruby 3.1.0+
https://bugs.ruby-lang.org/issues/19403#change-102490

* Author: [e-mail] (James Couball)
* Status: Closed
* Priority: Normal
* ruby -v: 3.2.0
* Backport: 2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONE, 3.2: DONE
----------------------------------------
# Unable to Build Native Gems on Mac with Ruby 3.1.0+

## Problem

In Ruby 3.1 and later installed by `rvm` or `asdf` on a Mac, `require 'mkmf'` aborts
the script and reports the following error (the reported path is different depending
on the Ruby install manager and the version of Ruby):

```text
mkmf.rb can't find header files for ruby at /Users/couballj/.asdf/installs/ruby/3.2.0/lib/ruby/include/ruby.h

You might have to install separate package for the ruby development
environment, ruby-dev or ruby-devel for example.
```

and `RbConfig::CONFIG["rubyhdrdir"]` is set to an incorrect path:

```text
"/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/Users/couballj/.asdf/installs/ruby/3.2.0/include/ruby-3.2.0"
```

## Expected Behavior

Running `require 'mkmf'` should not abort and for my system/user using `asdf` installed
Ruby 3.2.0 `RbConfig::CONFIG["rubyhdrdir"]` should be set to:

```text
"/Users/couballj/.asdf/installs/ruby/3.2.0/include/ruby-3.2.0"
```

## Details

In Ruby 3.1 and later I can no longer build native gems (like nokoguru or redcarpet)
on my Mac.

I have tried this by installing Ruby with both `rvm` and `asdf`, both which have
the same results.

I receive the following error when trying to install (and build) these gems. For
example, here is the error message when I try to run `gem install redcarpet`:

```text
mkmf.rb can't find header files for ruby at /Users/couballj/.asdf/installs/ruby/3.2.0/lib/ruby/include/ruby.h

You might have to install separate package for the ruby development
environment, ruby-dev or ruby-devel for example.
```

I found that this error could be triggered just by running a Ruby script that requires
`mkmf`. If `test.rb` contains this:

```ruby
require 'mkmf'
```

Running this script:

`ruby test.rb`

Results in this output:

```text
mkmf.rb can't find header files for ruby at /Users/couballj/.asdf/installs/ruby/3.2.0/lib/ruby/include/ruby.h

You might have to install separate package for the ruby development
environment, ruby-dev or ruby-devel for example.
```

Curiously, the reported directory does not exist. On my system, the path to `ruby.h`
is  `/Users/couballj/.asdf/installs/ruby/3.2.0/include/ruby-3.2.0/ruby.h`

I found where in the Ruby code this error is reported in [mkmf.rb line 233](https://github.com/ruby/ruby/blob/master/lib/mkmf.rb#L224-L233).

This code is trying to find `ruby.h` based on the value of `RbConfig::CONFIG["rubyhdrdir"]`.
On my system, this value is:

```ruby
"/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/Users/couballj/.asdf/installs/ruby/3.2.0/include/ruby-3.2.0"
```

This value is a concatenation of `ENV['SDKROOT']` (which on my system is `/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk`)
and the correct include directory path `/Users/couballj/.asdf/installs/ruby/3.2.0/include/ruby-3.2.0`.

When I run the same code with Ruby 2.7.7, `RbConfig::CONFIG["rubyhdrdir"]` is set to the correct path:

```ruby
"/Users/couballj/.asdf/installs/ruby/3.2.0/include/ruby-3.2.0"
```

## Possible Cause

I have found a possible cause in [commit fd97862](https://github.com/ruby/ruby/commit/fd978621ccbc9519afc05ad031ba2518e9a6f379#)
in line 127 of mkconfig.rb. This change prepends `ENV['SDKROOT']` to the include directory that
is used to build `RbConfig::CONFIG["rubyhdrdir"]`.

While there may have been good reason for that change, in my case this change causes
`require 'mkmf'` to fail in my use case.

## Work Around

I have been able to work around this issue by creating a symbolic link from
`/Users /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/Users` to `/Users`
with the following command:

```shell
sudo ln -s /Users /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/Users
```

This change will works for both `rvm` and `asdf` no matter what version of Ruby is
installed.




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