feat(mux): support http.Request.Pattern in Go 1.23

mux.go

@@ -476,6 +476,9 @@ func (mx *Mux) routeHTTP(w http.ResponseWriter, r *http.Request) {
 		if supportsPathValue {
 			setPathValue(rctx, r)
 		}
+		if supportsPattern {
+			setPattern(rctx, r)
+		}
 
 		h.ServeHTTP(w, r)
 		return

pattern.go

@@ -0,0 +1,16 @@
+//go:build go1.23 && !tinygo
+// +build go1.23,!tinygo
+
+package chi
+
+import "net/http"
+
+// supportsPattern is true if the Go version is 1.23 and above.
+//
+// If this is true, `net/http.Request` has field `Pattern`.
+const supportsPattern = true
+
+// setPattern sets the mux matched pattern in the http Request.
+func setPattern(rctx *Context, r *http.Request) {
+	r.Pattern = rctx.routePattern
+}

pattern_fallback.go

@@ -0,0 +1,17 @@
+//go:build !go1.23 || tinygo
+// +build !go1.23 tinygo
+
+package chi
+
+import "net/http"
+
+// supportsPattern is true if the Go version is 1.23 and above.
+//
+// If this is true, `net/http.Request` has field `Pattern`.
+const supportsPattern = false
+
+// setPattern sets the mux matched pattern in the http Request.
+//
+// setPattern is only supported in Go 1.23 and above so
+// this is just a blank function so that it compiles.
+func setPattern(rctx *Context, r *http.Request) {}

pattern_test.go

@@ -0,0 +1,56 @@
+//go:build go1.23
+// +build go1.23
+
+package chi
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestPattern(t *testing.T) {
+	testCases := []struct {
+		name        string
+		pattern     string
+		method      string
+		requestPath string
+	}{
+		{
+			name:        "Basic path value",
+			pattern:     "/hubs/{hubID}",
+			method:      "GET",
+			requestPath: "/hubs/392",
+		},
+		{
+			name:        "Two path values",
+			pattern:     "/users/{userID}/conversations/{conversationID}",
+			method:      "POST",
+			requestPath: "/users/Gojo/conversations/2948",
+		},
+		{
+			name:        "Wildcard path",
+			pattern:     "/users/{userID}/friends/*",
+			method:      "POST",
+			requestPath: "/users/Gojo/friends/all-of-them/and/more",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			r := NewRouter()
+
+			r.Handle(tc.method+" "+tc.pattern, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.Write([]byte(r.Pattern))
+			}))
+
+			ts := httptest.NewServer(r)
+			defer ts.Close()
+
+			_, body := testRequest(t, ts, tc.method, tc.requestPath, nil)
+			if body != tc.pattern {
+				t.Fatalf("expecting %q, got %q", tc.pattern, body)
+			}
+		})
+	}
+}