Cmatch: Do not fail given __classes question

* src/client/Cmatch.js (handleClassMatch): Rename from
  _handleClassMatch.  Make protected.  Check for truthy `vis'.
* test/client/CmatchTest.js: Update accordingly.

src/client/Cmatch.js

@@ -150,7 +150,7 @@ module.exports = Class( 'Cmatch',
                         return;
                     }
 
-                    _self._handleClassMatch( cmatch );
+                    _self.handleClassMatch( cmatch );
                     cmatchprot = false;
                 } );
             } );
@@ -224,7 +224,7 @@ module.exports = Class( 'Cmatch',
     },
 
 
-    'private _handleClassMatch': function( cmatch, force )
+    'virtual protected handleClassMatch': function( cmatch, force )
     {
         force = !!force;
 
@@ -268,6 +268,12 @@ module.exports = Class( 'Cmatch',
                     || []
                 );
 
+            // this should really only ever be the case for __classes
+            if ( !vis )
+            {
+                continue;
+            }
+
             // TODO: Figure out something better here.  This is currently
             // needed for hiding statics---they are registered as exclusive
             // fields (`fields', above), but aren't actually fields (they're
@@ -494,7 +500,7 @@ module.exports = Class( 'Cmatch',
             return this;
         }
 
-        this._handleClassMatch( this._cmatch, true );
+        this.handleClassMatch( this._cmatch, true );
 
         return this;
     },

test/client/CmatchTest.js

@@ -25,13 +25,22 @@ const { expect } = require( 'chai' );
 const Sut = require( '../../src/client/Cmatch' )
     .extend(
 {
-    'override constructor'( _, __, ___ ) {},
+    'override constructor'( class_matcher, program, client )
+    {
+        this.__super( class_matcher || {}, program || {}, client || {} );
+    },
 
     // make public
     'override public markShowHide'( field, visq, show, hide )
     {
         return this.__super( field, visq, show, hide );
-    }
+    },
+
+    // make public
+    'override public handleClassMatch'( cmatch, force )
+    {
+        this.__super( cmatch, force );
+    },
 } );
 
 
@@ -84,4 +93,38 @@ describe( "Cmatch", () =>
 
         expect( visq.bar ).to.equal( barval );
     } );
+
+
+    /**
+     * __classes is always returned (at least at the time of writing) by
+     * TAME.  here was a bug when it was recognized as a field (e.g. marked
+     * as an `external' in program.xml),
+     */
+    it( "does not fail when __classes is a known field", () =>
+    {
+        const cmatch = {
+            // populated by TAME, always
+            __classes: {},
+        };
+
+        const field_names = {
+            __classes: true,
+        };
+
+        const mock_client = {
+            getUi: () => ( {
+                setCmatch() {},
+                getCurrentStep: () => ( {
+                    getStep: () => ( {
+                        getExclusiveFieldNames: () => field_names,
+                    } )
+                } )
+            } ),
+            getQuote: () => ( {} ),
+        };
+
+        Sut( {}, {}, mock_client ).handleClassMatch(
+            cmatch, false
+        );
+    } );
 } );