compile time validation of path (#2350)

* compile time validation of path

* added trybuild err message

* Update Cargo.toml

* add changelog entry

* test more cases of path validation

* fmt

Co-authored-by: Rob Ede <robjtede@icloud.com>

actix-web-codegen/tests/trybuild/route-malformed-path-fail.rs

@@ -0,0 +1,33 @@
+use actix_web_codegen::get;
+
+#[get("/{")]
+async fn zero() -> &'static str {
+    "malformed resource def"
+}
+
+#[get("/{foo")]
+async fn one() -> &'static str {
+    "malformed resource def"
+}
+
+#[get("/{}")]
+async fn two() -> &'static str {
+    "malformed resource def"
+}
+
+#[get("/*")]
+async fn three() -> &'static str {
+    "malformed resource def"
+}
+
+#[get("/{tail:\\d+}*")]
+async fn four() -> &'static str {
+    "malformed resource def"
+}
+
+#[get("/{a}/{b}/{c}/{d}/{e}/{f}/{g}/{h}/{i}/{j}/{k}/{l}/{m}/{n}/{o}/{p}/{q}")]
+async fn five() -> &'static str {
+    "malformed resource def"
+}
+
+fn main() {}