fix: improve Objective-C vs Mathematica disambiguation for .m files

fix: improve Objective-C vs Mathematica disambiguation for .m files

The previous logic would incorrectly identify Objective-C code as Mathematica
when encountering pointer dereference syntax like `if (*foo == 0)`, since it
looked similar to Mathematica's comment syntax `(* comment *)`.

This change improves the disambiguation by:
1. Only matching Mathematica comments that start at beginning of line
2. Adding an additional Objective-C identifier for braces at end of line

lib/rouge/guessers/disambiguation.rb

@@ -90,8 +90,13 @@ def match?(filename)
       disambiguate '*.m' do
         next ObjectiveC if matches?(/@(end|implementation|protocol|property)\b/)
         next ObjectiveC if contains?('@"')
-
-        next Mathematica if contains?('(*')
+        # Opening brace at end of line
+        next ObjectiveC if matches?(/\s*{\s*$/)
+
+        # Objective-C may use dereferenced pointers in statements: `if (*foo == 0)`.
+        # This is similar to Mathmatica's comment syntax: `(* comment *)`.
+        # Disambiguate by checking for any amount of whitespace (or no whitespace) followed by (*
+        next Mathematica if matches?(/^\s*\(\*/)
         next Mathematica if contains?(':=')
 
         next Mason if matches?(/<%(def|method|text|doc|args|flags|attr|init|once|shared|perl|cleanup|filter)([^>]*)(>)/)

spec/lexers/objective_c_spec.rb

@@ -19,6 +19,7 @@
     it 'guesses by source' do
       assert_guess :filename => 'foo.h', :source => '@"foo"'
       assert_guess :filename => 'foo.h', :source => '@implementation Foo'
+      assert_guess :filename => 'foo.m', :source => 'if (*bar == 0) {'
     end
   end
 end