Improve Objective-C vs Mathematica lexer disambiguation (#2103)

* 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

* resolve disambiguation conflict, add more test cases

Author: EthanArbuckle

lib/rouge/guessers/disambiguation.rb

@@ -90,14 +90,24 @@ def match?(filename)
       disambiguate '*.m' do
         next ObjectiveC if matches?(/@(end|implementation|protocol|property)\b/)
         next ObjectiveC if contains?('@"')
+        
+        # Objective-C dereferenced pointers and Mathematica comments are similar.
+        # Disambiguate for Mathematica by looking for any amount of whitespace (or no whitespace)
+        # followed by "(*" (e.g. `(* comment *)`).
+        next Mathematica if matches?(/^\s*\(\*/)
+
+        # Disambiguate for objc by looking for a deref'd pointer in a statement (e.g. `if (*foo == 0)`).
+        # This pattern is less specific than the Mathematica pattern, so its positioned after it.
+        next ObjectiveC if matches?(/^\s*(if|while|for|switch|do)\s*\([^)]*\*[^)]*\)/)
 
-        next Mathematica if contains?('(*')
         next Mathematica if contains?(':=')
 
         next Mason if matches?(/<%(def|method|text|doc|args|flags|attr|init|once|shared|perl|cleanup|filter)([^>]*)(>)/)
 
         next Matlab if matches?(/^\s*?%/)
-
+        # Matlab cell array creation: data = {
+        next Matlab if matches?(/^\s*[a-zA-Z]\w*\s*=\s*\{/)
+        
         next Mason if matches? %r!(</?%|<&)!
       end
 

spec/lexers/mathematica_spec.rb

@@ -16,5 +16,10 @@
       assert_guess :mimetype => 'application/vnd.wolfram.mathematica.package'
       assert_guess :mimetype => 'application/vnd.wolfram.wl'
     end
+
+    it 'guesses by source' do
+      assert_guess :filename => 'foo.m', :source => '(* Mathematica comment *)'
+      assert_guess :filename => 'foo.m', :source => 'a := b'
+    end
   end
 end

spec/lexers/matlab_spec.rb

@@ -33,5 +33,10 @@
       end
       eos
     end
+
+    it 'guesses by source' do
+      assert_guess :filename => 'foo.m', :source => '% MATLAB comment'
+      assert_guess :filename => 'foo.m', :source => 'mycell = {'
+    end
   end
 end

spec/lexers/objective_c_spec.rb

@@ -19,6 +19,9 @@
     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) {'
+      assert_guess :filename => 'foo.m', :source => 'while (*ptr != NULL)'
+      assert_guess :filename => 'foo.m', :source => 'if (*(void **)(addr + 8) == target) {'
     end
   end
 end