feat: disallow regexp constraint in optional wildcards (#77)

Author: tigerwill90

README.md

@@ -199,8 +199,9 @@ Pattern /src/file=*{path}
 /src/file=                          matches
 ````
 
-Named wildcard can include regular expression using the syntax `+{name:regexp}` or `*{name:regexp}`. Regular expressions cannot
-contain capturing groups, but can use non-capturing groups `(?:pattern)` instead. Regexp support is opt-in via `fox.AllowRegexpParam(true)` option.
+Named wildcards can include a regular expression constraint using the syntax `+{name:regexp}`. Regular expressions cannot
+contain capturing groups, but can use non-capturing groups `(?:pattern)` instead. Optional wildcards (`*{param}`) do not
+support regular expressions. Regexp support is opt-in via `fox.AllowRegexpParam(true)` option.
 
 ````
 Pattern /src/+{filepath:[A-Za-z/]+\.json}

fox.go

@@ -1212,6 +1212,12 @@ func (fox *Router) parseRoute(url string) (parsedRoute, error) {
 			}
 
 			if url[i] == ':' {
+				// Optional wildcards (*{param}) do not support regular expressions because they match
+				// empty strings, making it impossible to disambiguate routes with different regexps that
+				// both match the same empty-string path.
+				if url[startCatchAll] == '*' {
+					return parsedRoute{}, fmt.Errorf("%w: %w in optional wildcard", ErrInvalidRoute, ErrRegexpNotAllowed)
+				}
 				previous = state
 				state = stateRegex
 				i++

fox_test.go

@@ -3282,6 +3282,11 @@ func TestParseRoute(t *testing.T) {
 			path:    "/foo/{:}",
 			wantErr: ErrInvalidRoute,
 		},
+		{
+			name:    "unsupported regexp in optional wildcard",
+			path:    "/foo/*{any:[A-z]+}",
+			wantErr: ErrInvalidRoute,
+		},
 		{
 			name:    "unbalanced braces in param regexp",
 			path:    "/foo/{bar:[A-z]+",
@@ -4825,9 +4830,7 @@ func TestTree_Has(t *testing.T) {
 		"/users/uid_{id:[A-z]+}/ch",
 		"/john/doe/",
 		"/foo/*{name}",
-		"/foo/*{name:[A-z]+}",
 		"/foo/uid_*{id}",
-		"/foo/uid_*{id:[A-z]+}",
 	}
 
 	f, _ := NewRouter(AllowRegexpParam(true))