soft deprecate `NormalizePath::default`

CHANGES.md

@@ -1,6 +1,10 @@
 # Changes
 
 ## Unreleased - 2020-xx-xx
+### Changed
+* Soft-deprecate `NormalizePath::default()`, noting upcoming behavior change in v4. [#2529]
+
+[#2529]: https://github.com/actix/actix-web/pull/2529
 
 
 ## 3.3.2 - 2020-12-01

actix-http/src/error.rs

@@ -55,7 +55,7 @@ impl Error {
 
     /// Similar to `as_response_error` but downcasts.
     pub fn as_error<T: ResponseError + 'static>(&self) -> Option<&T> {
-        ResponseError::downcast_ref(self.cause.as_ref())
+        <dyn ResponseError>::downcast_ref(self.cause.as_ref())
     }
 }
 

src/middleware/normalize.rs

@@ -31,7 +31,7 @@ impl Default for TrailingSlash {
     }
 }
 
-#[derive(Default, Clone, Copy)]
+#[derive(Clone, Copy)]
 /// `Middleware` to normalize request's URI in place
 ///
 /// Performs following:
@@ -56,6 +56,18 @@ impl Default for TrailingSlash {
 
 pub struct NormalizePath(TrailingSlash);
 
+impl Default for NormalizePath {
+    fn default() -> Self {
+        log::warn!(
+            "`NormalizePath::default()` is deprecated. The default trailing slash behavior will \
+            change in v4 from `Always` to `Trim`. Update your call to `NormalizePath::new(...)` to \
+            avoid inaccessible routes when upgrading."
+        );
+
+        Self(TrailingSlash::default())
+    }
+}
+
 impl NormalizePath {
     /// Create new `NormalizePath` middleware with the specified trailing slash style.
     pub fn new(trailing_slash_style: TrailingSlash) -> Self {