[ruby/prism] Rewrite "version: nearest" to require no maintenance

Currently I see myself not updating this when a new version is added.

Instead, rewrite it to just work with new versions:
* Try to set the version
* If that doesn't succeed, check if it is lower
* If it isn't lower, it must be higher

We can then use `PM_OPTIONS_VERSION_LATEST` which doesn't need to change.

Also added a very basic test.

https://github.com/ruby/prism/commit/443e9b9959

1 files changed, 19 insertions, 24 deletions

diff --git a/lib/prism/ffi.rb b/lib/prism/ffi.rb
index 57d878a33f..618324ded6 100644
--- a/lib/prism/ffi.rb
+++ b/lib/prism/ffi.rb
@@ -423,27 +423,28 @@ module Prism
 
     # Return the value that should be dumped for the version option.
     def dump_options_version(version)
-      checking =
-        case version
-        when "current"
-          RUBY_VERSION
-        when "latest"
-          nil
-        when "nearest"
-          if RUBY_VERSION <= "3.3"
-            "3.3"
-          elsif RUBY_VERSION >= "4.1"
-            "4.1"
-          else
-            RUBY_VERSION
-          end
+      case version
+      when "current"
+        version_string_to_number(RUBY_VERSION) || raise(CurrentVersionError, RUBY_VERSION)
+      when "latest", nil
+        0 # Handled in pm_parser_init
+      when "nearest"
+        dump = version_string_to_number(RUBY_VERSION)
+        return dump if dump
+        if RUBY_VERSION < "3.3"
+          version_string_to_number("3.3")
         else
-          version
+          0 # Handled in pm_parser_init
         end
+      else
+        version_string_to_number(version) || raise(ArgumentError, "invalid version: #{version}")
+      end
+    end
 
-      case checking
-      when nil
-        0 # Handled in pm_parser_init
+    # Converts a version string like "4.0.0" or "4.0" into a number.
+    # Returns nil if the version is unknown.
+    def version_string_to_number(version)
+      case version
       when /\A3\.3(\.\d+)?\z/
         1
       when /\A3\.4(\.\d+)?\z/
@@ -452,12 +453,6 @@ module Prism
         3
       when /\A4\.1(\.\d+)?\z/
         4
-      else
-        if version == "current"
-          raise CurrentVersionError, RUBY_VERSION
-        else
-          raise ArgumentError, "invalid version: #{version}"
-        end
       end
     end