Revert "[bugfix] fail fast if regex is incorrectly specified using capturing groups. (gorilla#218)"

This reverts commit 392c28f.

Author: ldez

doc.go

@@ -57,11 +57,6 @@ calling mux.Vars():
 	vars := mux.Vars(request)
 	category := vars["category"]
 
-Note that if any capturing groups are present, mux will panic() during parsing. To prevent
-this, convert any capturing groups to non-capturing, e.g. change "/{sort:(asc|desc)}" to
-"/{sort:(?:asc|desc)}". This is a change from prior versions which behaved unpredictably
-when capturing groups were present.
-
 And this is all you need to know about the basic usage. More advanced options
 are explained below.
 

mux_test.go

@@ -1757,16 +1757,6 @@ func TestSubrouterErrorHandling(t *testing.T) {
 	}
 }
 
-// See: https://github.com/gorilla/mux/issues/200
-func TestPanicOnCapturingGroups(t *testing.T) {
-	defer func() {
-		if recover() == nil {
-			t.Errorf("(Test that capturing groups now fail fast) Expected panic, however test completed successfully.\n")
-		}
-	}()
-	NewRouter().NewRoute().Path("/{type:(promo|special)}/{promoId}.json")
-}
-
 // ----------------------------------------------------------------------------
 // Helpers
 // ----------------------------------------------------------------------------

regexp.go

@@ -129,13 +129,6 @@ func newRouteRegexp(tpl string, typ regexpType, options routeRegexpOptions) (*ro
 	if errCompile != nil {
 		return nil, errCompile
 	}
-
-	// Check for capturing groups which used to work in older versions
-	if reg.NumSubexp() != len(idxs)/2 {
-		panic(fmt.Sprintf("route %s contains capture groups in its regexp. ", template) +
-			"Only non-capturing groups are accepted: e.g. (?:pattern) instead of (pattern)")
-	}
-
 	// Done!
 	return &routeRegexp{
 		template:         template,