Ensure that Gem::Platform parses strings to a fix point

[segiddins]

The issue was that the property that

platform = Gem::Platform.new $string
platform == Gem::Platform.new(platform.to_s)

was not always true.

This property (of acchieving a fix point) is important,
since Gem::Platform gets serialized to a string and
then deserialized back to a Gem::Platform object.
If it doesn't deserialize to the same object, then
different platforms are used for the initial serialization
than subsequent runs.

I used https://github.com/segiddins/Scratch/blob/main/2025/03/rubygems-platform.rb
to find the failing cases and then fixed them.
With this patch, the prop check test now passes.

What was the end-user or developer problem that led to this PR?

What is your fix for the problem, implemented in this PR?

Make sure the following tasks are checked

• Describe the problem / feature
• Write tests for features and bug fixes
• Write code to solve the problem
• Make sure you follow the current code style and write meaningful commit messages without tags

[deivid-rodriguez]

Nice! Indeed it seems important to make that property hold, and nice job finding failing test cases.

At this point, I think the implementation of Gem::Platform#initialize is too complicated so I gave simplifying it a try, while also trying to make this property hold.

How about the following:

diff --git a/lib/rubygems/platform.rb b/lib/rubygems/platform.rb
index 450c2141676..ebb7f3dcdae 100644
--- a/lib/rubygems/platform.rb
+++ b/lib/rubygems/platform.rb
@@ -88,56 +88,44 @@ def initialize(arch)
     when Array then
       @cpu, @os, @version = arch
     when String then
-      arch = arch.split "-"
-
-      if arch.length > 2 && !arch.last.match?(/\d+(\.\d+)?$/) # reassemble x86-linux-{libc}
-        extra = arch.pop
-        arch.last << "-#{extra}"
-      end
-
-      cpu = arch.shift
+      cpu, os = arch.gsub(/-+$/, "").split "-", 2
 
       @cpu = case cpu
              when /i\d86/ then "x86"
              else cpu
       end
 
-      if arch.length == 2 && arch.last.match?(/^\d+(\.\d+)?$/) # for command-line
-        @os, @version = arch
-        return
-      end
-
-      os, = arch
       if os.nil?
         @cpu = nil
         os = cpu
       end # legacy jruby
 
       @os, @version = case os
-                      when /aix(\d+)?/ then             ["aix",       $1]
+                      when /aix-?(\d+)?/ then           ["aix",       $1]
                       when /cygwin/ then                ["cygwin",    nil]
-                      when /darwin(\d+)?/ then          ["darwin",    $1]
+                      when /darwin-?(\d+)?/ then        ["darwin",    $1]
                       when /^macruby$/ then             ["macruby",   nil]
-                      when /freebsd(\d+)?/ then         ["freebsd",   $1]
+                      when /^macruby-?([\d.]+)?/ then   ["macruby",   $1]
+                      when /freebsd-?(\d+)?/ then       ["freebsd",   $1]
                       when /^java$/, /^jruby$/ then     ["java",      nil]
-                      when /^java([\d.]*)/ then         ["java",      $1]
-                      when /^dalvik(\d+)?$/ then        ["dalvik",    $1]
+                      when /^java-?(\d+(?:\.\d+)*)?/ then ["java",    $1]
+                      when /^dalvik-?(\d+)?$/ then      ["dalvik",    $1]
                       when /^dotnet$/ then              ["dotnet",    nil]
-                      when /^dotnet([\d.]*)/ then       ["dotnet",    $1]
+                      when /^dotnet-?(\d+(?:\.\d+)*)?/ then ["dotnet", $1]
                       when /linux-?(\w+)?/ then         ["linux",     $1]
                       when /mingw32/ then               ["mingw32",   nil]
                       when /mingw-?(\w+)?/ then         ["mingw",     $1]
-                      when /(mswin\d+)(\_(\d+))?/ then
+                      when /(mswin\d+)[-_]?(\d+)?/ then
                         os = $1
-                        version = $3
+                        version = $2
                         @cpu = "x86" if @cpu.nil? && os =~ /32$/
                         [os, version]
                       when /netbsdelf/ then             ["netbsdelf", nil]
-                      when /openbsd(\d+\.\d+)?/ then    ["openbsd",   $1]
-                      when /solaris(\d+\.\d+)?/ then    ["solaris",   $1]
+                      when /openbsd-?(\d+\.\d+)?/ then  ["openbsd",   $1]
+                      when /solaris-?(\d+\.\d+)?/ then  ["solaris",   $1]
                       when /wasi/ then                  ["wasi",      nil]
                       # test
-                      when /^(\w+_platform)(\d+)?/ then [$1,          $2]
+                      when /^(\w+_platform)-?(\d+)?/ then [$1, $2]
                       else ["unknown", nil]
       end
     when Gem::Platform then
@@ -154,7 +142,7 @@ def to_a
   end
 
   def to_s
-    to_a.compact.join "-"
+    to_a.compact.join(@cpu.nil? ? "" : "-")
   end
 
   ##

Also, while looking into this I found one case that your initial patch did not catch: x86_64-macruby-x86, and I'd also suggest to add x86_64-dotnetx86, x86_64-dalvik0, and x86_64-dotnet1., because I did not get those right initially and only caught them after running your script to find issues against my initial patch.

[segiddins]

@deivid-rodriguez done!

[deivid-rodriguez]

Mmm, I must've messed something up because this seems to break existing specs 🤔

[deivid-rodriguez]

Figured it out, a small tweak was missing from the diff I had proposed.