Bundler 1.17 / Rubygems 3.0 linux-musl resolution

Gemfile

# This fixes the platform value for rubygems 3.x, allowing bundler and gem install
# to properly resolve to: a) linux on linux, and b) to linux-musl on linux-musl
# with a fallback to linux if there's no linux-musl gem published.
#
# This works when there is no extension to build that would try to query the
# current Ruby platform through Rubygems (because building an extension spawns an
# independent Ruby interpreter)
#
# The second file in this gist is a patch to apply to Rubygems 3.0.3.1, e.g for
# official Docker Hub images:
#
# ```
# cat musl.patch | (cd /usr/local/lib/ruby/2.6.0/rubygems && patch -p1)
# ```

module Gem::Platform::Patch
  def initialize(arch)
    case arch
    when Array then
      @cpu, @os, @version = arch
    when String then
      arch = arch.split '-'

      if arch.length > 2 and arch.last !~ /\d+(\.\d+)?$/ # reassemble x86-linux-{libc}
        extra = arch.pop
        arch.last << "-#{extra}"
      end

      cpu = arch.shift

      @cpu = case cpu
            when /i\d86/ then 'x86'
            else cpu
            end

      if arch.length == 2 and arch.last =~ /^\d+(\.\d+)?$/ # for command-line
        @os, @version = arch
        return
      end

      os, = arch
      @cpu, os = nil, cpu if os.nil? # legacy jruby

      @os, @version = case os
                      when /aix(\d+)?/ then             [ 'aix',       $1  ]
                      when /cygwin/ then                [ 'cygwin',    nil ]
                      when /darwin(\d+)?/ then          [ 'darwin',    $1  ]
                      when /^macruby$/ then             [ 'macruby',   nil ]
                      when /freebsd(\d+)?/ then         [ 'freebsd',   $1  ]
                      when /hpux(\d+)?/ then            [ 'hpux',      $1  ]
                      when /^java$/, /^jruby$/ then     [ 'java',      nil ]
                      when /^java([\d.]*)/ then         [ 'java',      $1  ]
                      when /^dalvik(\d+)?$/ then        [ 'dalvik',    $1  ]
                      when /^dotnet$/ then              [ 'dotnet',    nil ]
                      when /^dotnet([\d.]*)/ then       [ 'dotnet',    $1  ]
                      when /linux-?((?!gnu)\w+)?/ then  [ 'linux',     $1  ]
                      when /mingw32/ then               [ 'mingw32',   nil ]
                      when /(mswin\d+)(\_(\d+))?/ then
                        os, version = $1, $3
                        @cpu = 'x86' if @cpu.nil? and os =~ /32$/
                        [os, version]
                      when /netbsdelf/ then             [ 'netbsdelf', nil ]
                      when /openbsd(\d+\.\d+)?/ then    [ 'openbsd',   $1  ]
                      when /bitrig(\d+\.\d+)?/ then     [ 'bitrig',    $1  ]
                      when /solaris(\d+\.\d+)?/ then    [ 'solaris',   $1  ]
                      # test
                      when /^(\w+_platform)(\d+)?/ then [ $1,          $2  ]
                      else                              [ 'unknown',   nil ]
                      end
    when Gem::Platform then
      @cpu = arch.cpu
      @os = arch.os
      @version = arch.version
    else
      raise ArgumentError, "invalid argument #{arch.inspect}"
    end
  end

  def ===(other)
    return nil unless Gem::Platform === other

    # cpu
    ([nil,'universal'].include?(@cpu) or [nil, 'universal'].include?(other.cpu) or @cpu == other.cpu or (@cpu == 'arm' and other.cpu.start_with?("arm"))) and

    # os
    @os == other.os and

    # version
    (
      (@os != 'linux' and (@version.nil? or other.version.nil?)) or
      (@os == 'linux' and (!@version.nil? and other.version.nil?)) or
      @version == other.version
    )
  end
end

# apply monkeypatch
Gem::Platform.prepend Gem::Platform::Patch
# reset cached values
Gem::Platform.instance_eval { @local = nil }
Gem.instance_eval { @platforms = nil }

source 'https://rubygems.org'

gem 'libv8-node'
gem 'nokogiri'

musl.patch

diff --git a/platform.orig b/platform.rb
index f8fe4da..93e9dee 100644
--- a/platform.orig
+++ b/platform.rb
@@ -56,7 +56,7 @@ class Gem::Platform
     when String then
       arch = arch.split '-'
 
-      if arch.length > 2 and arch.last !~ /\d/  # reassemble x86-linux-gnu
+      if arch.length > 2 and arch.last !~ /\d+(\.\d+)?$/ # reassemble x86-linux-{libc}
         extra = arch.pop
         arch.last << "-#{extra}"
       end
@@ -64,11 +64,11 @@ class Gem::Platform
       cpu = arch.shift
 
       @cpu = case cpu
-             when /i\d86/ then 'x86'
-             else cpu
-             end
+            when /i\d86/ then 'x86'
+            else cpu
+            end
 
-      if arch.length == 2 and arch.last =~ /^\d+(\.\d+)?$/  # for command-line
+      if arch.length == 2 and arch.last =~ /^\d+(\.\d+)?$/ # for command-line
         @os, @version = arch
         return
       end
@@ -88,7 +88,7 @@ class Gem::Platform
                       when /^dalvik(\d+)?$/ then        [ 'dalvik',    $1  ]
                       when /^dotnet$/ then              [ 'dotnet',    nil ]
                       when /^dotnet([\d.]*)/ then       [ 'dotnet',    $1  ]
-                      when /linux/ then                 [ 'linux',     $1  ]
+                      when /linux-?((?!gnu)\w+)?/ then  [ 'linux',     $1  ]
                       when /mingw32/ then               [ 'mingw32',   nil ]
                       when /(mswin\d+)(\_(\d+))?/ then
                         os, version = $1, $3
@@ -149,16 +149,20 @@ class Gem::Platform
     return nil unless Gem::Platform === other
 
     # cpu
-    ([nil,'universal'].include?(@cpu) or [nil, 'universal'].include?(other.cpu) or @cpu == other.cpu or
-    (@cpu == 'arm' and other.cpu =~ /\Aarm/)) and
+    ([nil,'universal'].include?(@cpu) or [nil, 'universal'].include?(other.cpu) or @cpu == other.cpu or (@cpu == 'arm' and other.cpu.start_with?("arm"))) and
 
     # os
     @os == other.os and
 
     # version
-    (@version.nil? or other.version.nil? or @version == other.version)
+    (
+      (@os != 'linux' and (@version.nil? or other.version.nil?)) or
+      (@os == 'linux' and (!@version.nil? and other.version.nil?)) or
+      @version == other.version
+    )
   end
 
+
   ##
   # Does +other+ match this platform?  If +other+ is a String it will be
   # converted to a Gem::Platform first.  See #=== for matching rules.

Bless you for posting this. Was bashing my head for days trying to get a legacy project to build consistently.