feat(macros): add compile-time validations to TypedPath macro (#3797)

axum-macros/src/typed_path.rs

@@ -386,6 +386,8 @@ fn parse_path(path: &LitStr) -> syn::Result<Vec<Segment>> {
         return Err(syn::Error::new_spanned(path, "paths must start with a `/`"));
     }
 
+    validate_path_segments(&value, path)?;
+
     let mut segments = Vec::new();
     let mut rest = value.as_str();
 
@@ -421,6 +423,46 @@ fn parse_path(path: &LitStr) -> syn::Result<Vec<Segment>> {
     Ok(segments)
 }
 
+fn validate_path_segments(value: &str, path: &LitStr) -> syn::Result<()> {
+    let mut wildcard_seen = false;
+
+    for segment in value.split('/') {
+        if wildcard_seen {
+            return Err(syn::Error::new_spanned(
+                path,
+                "Wildcards must be at the end of the path",
+            ));
+        }
+
+        let mut capture_count = 0;
+        let mut rest = segment;
+        while let Some(start) = find_first_not_double(b'{', rest.as_bytes()) {
+            capture_count += 1;
+            rest = &rest[start + 1..];
+
+            if rest.starts_with('*') {
+                wildcard_seen = true;
+                // a wildcard capture must cover its entire segment
+                if start != 0 || rest.find('}') != Some(rest.len() - 1) {
+                    return Err(syn::Error::new_spanned(
+                        path,
+                        "Wildcards must be at the end of the path",
+                    ));
+                }
+            }
+        }
+
+        if capture_count > 1 {
+            return Err(syn::Error::new_spanned(
+                path,
+                "Cannot have multiple path parameters in a single segment",
+            ));
+        }
+    }
+
+    Ok(())
+}
+
 fn find_first_not_double(needle: u8, haystack: &[u8]) -> Option<usize> {
     let mut possible_capture = 0;
     while let Some(index) = haystack

axum-macros/tests/typed_path/fail/catch_all_not_at_end.rs

@@ -0,0 +1,10 @@
+use axum_macros::TypedPath;
+use serde::Deserialize;
+
+#[derive(TypedPath, Deserialize)]
+#[typed_path("/{*rest}/foo")]
+struct MyPath {
+    rest: String,
+}
+
+fn main() {}

axum-macros/tests/typed_path/fail/catch_all_not_at_end.stderr

@@ -0,0 +1,5 @@
+error: Wildcards must be at the end of the path
+ --> tests/typed_path/fail/catch_all_not_at_end.rs:5:14
+  |
+5 | #[typed_path("/{*rest}/foo")]
+  |              ^^^^^^^^^^^^^^

axum-macros/tests/typed_path/fail/catch_all_not_whole_segment.rs

@@ -0,0 +1,10 @@
+use axum_macros::TypedPath;
+use serde::Deserialize;
+
+#[derive(TypedPath, Deserialize)]
+#[typed_path("/files/{*rest}.txt")]
+struct MyPath {
+    rest: String,
+}
+
+fn main() {}

axum-macros/tests/typed_path/fail/catch_all_not_whole_segment.stderr

@@ -0,0 +1,5 @@
+error: Wildcards must be at the end of the path
+ --> tests/typed_path/fail/catch_all_not_whole_segment.rs:5:14
+  |
+5 | #[typed_path("/files/{*rest}.txt")]
+  |              ^^^^^^^^^^^^^^^^^^^^

axum-macros/tests/typed_path/fail/multiple_params_in_segment.rs

@@ -0,0 +1,11 @@
+use axum_macros::TypedPath;
+use serde::Deserialize;
+
+#[derive(TypedPath, Deserialize)]
+#[typed_path("/user-{first}-{last}")]
+struct MyPath {
+    first: String,
+    last: String,
+}
+
+fn main() {}

axum-macros/tests/typed_path/fail/multiple_params_in_segment.stderr

@@ -0,0 +1,5 @@
+error: Cannot have multiple path parameters in a single segment
+ --> tests/typed_path/fail/multiple_params_in_segment.rs:5:14
+  |
+5 | #[typed_path("/user-{first}-{last}")]
+  |              ^^^^^^^^^^^^^^^^^^^^^^