[ruby/syntax_suggest] Refactor multi-prism version logic

The reason this logic for different methods branches in the class instead of internally was to be eagerly aggressive about runtime performance. This code is currently only used once for the document where it's invoked ~N times (where N is number of lines):

```ruby
module SyntaxSuggest
  class CleanDocument
    # ...
    def join_trailing_slash!
      trailing_groups = @document.select(&:trailing_slash?).map do |code_line|
        take_while_including(code_line.index..) { |x| x.trailing_slash? }
      end
      join_groups(trailing_groups)
      self
    end
```

Since this is not currently a hot-spot I think merging the branches and using a case statement is a reasonable tradeoff and avoids the need to do specific version testing.

An alternative idea was presented in #241 of behavior-based testing for branch logic (which I would prefer), however, calling the code triggered requiring a `DelegateClass` when the `syntax_suggest/api` is being required.

https://github.com/ruby/syntax_suggest/commit/ab122c455f

1 files changed, 9 insertions, 13 deletions

diff --git a/lib/syntax_suggest/code_line.rb b/lib/syntax_suggest/code_line.rb
index 892c273c41..76ca892ac3 100644
--- a/lib/syntax_suggest/code_line.rb
+++ b/lib/syntax_suggest/code_line.rb
@@ -180,21 +180,17 @@ module SyntaxSuggest
     #     EOM
     #     expect(lines.first.trailing_slash?).to eq(true)
     #
-    if SyntaxSuggest.use_prism_parser? && Prism::VERSION <= "1.8.0"
-      # Older versions of prism didn't correctly emit on_sp
-      def trailing_slash?
-        last = @lex.last
-        return false unless last
-
-        last.type == :on_tstring_end || (last.type == :on_sp && last.token == TRAILING_SLASH)
-      end
-    else
-      def trailing_slash?
-        last = @lex.last
-        return false unless last
-        return false unless last.type == :on_sp
+    def trailing_slash?
+      last = @lex.last
 
+      # Older versions of prism diverged slightly from Ripper in compatibility mode
+      case last&.type
+      when :on_sp
         last.token == TRAILING_SLASH
+      when :on_tstring_end
+        true
+      else
+        false
       end
     end