Having the same issue with subroutes:

import (
	"fmt"
	"net/http"

	"github.com/go-chi/chi/v5"
)

func empty(w http.ResponseWriter, r *http.Request) {}

func main() {
	r := chi.NewRouter()
	r.Route("/{:[1-9]\\d*}", func(r chi.Router) {
		r.Get(`/test`, empty)
	})

	ctx := chi.NewRouteContext()
	if r.Match(ctx, "GET", "/123/test") {
		fmt.Println("The route matched the URL.")
	}
	if r.Match(ctx, "GET", "//test") {
		fmt.Println("The route matched the URL.")
	}
}

Second match is not expected.

One note about empty route segments is that some browser (like Chrome) will automatically remove them during URL normalization. It's still probably correct to consider this a bug, but in practice having empty route segments should be discouraged due to the fact that the user may not be able to navigate to them.

This bug is caused by not setting xn to nil in time when ntype is equal to ntRegexp and traversing the child nodes.
the xn in these places should be set to empty in time.tree.go#L432、tree.go#L438、tree.go#L442.

I want to fix this bug, please assign this issue to me.
@pkieltyka

Having the same issue with subroutes:

import (
	"fmt"
	"net/http"

	"github.com/go-chi/chi/v5"
)

func dummy(w http.ResponseWriter, r *http.Request) {}

func main() {
	r := chi.NewRouter()
	r.Route(`/{handle:[a-zA-Z\d._-]+}`, func(r chi.Router) {
		r.Get(`/`, dummy)
		// ...
	})
	http.ListenAndServe(":3333", r)
}

With this example, http://localhost:3333// will also match the route even if + is used in the regex which requires at least one character in the parameter.

any progress for #609 (comment) @pkieltyka

Surprising this bug still exists many years later. The work around I'm looking into using right now is:

// ...

r.Route("//", func(r chi.Router) {
    // blackhole *//* requests
})

r.Route("/key:[a-z]+"), func(r chi.Router) {
    // ...
})

// ...

chi will reply with 404 page not found

Alternatively you can just use a middleware that ensures the parameter matches your regex manually.