perf: improve to_file_path()

url/src/lib.rs

@@ -2720,17 +2720,25 @@
                 _ => return Err(()),
             };
 
-            let estimated_capacity = self.as_str().len()
-                - if cfg!(target_os = "redox") {
-                    // remove only // because it still has file:
-                    2
-                } else if cfg!(windows) {
-                    // remove file: - has posssible \\ for hostname
-                    5
+            let str_len = self.as_str().len();
+            let estimated_capacity = if cfg!(target_os = "redox") {
+                let scheme_len = self.scheme().len();
+                let file_scheme_len = "file".len();
+                // remove only // because it still has file:
+                if scheme_len < file_scheme_len {
+                    let scheme_diff = file_scheme_len - scheme_len;
+                    (str_len + scheme_diff).saturating_sub(2)
                 } else {
-                    // remove file://
-                    7
-                };
+                    let scheme_diff = scheme_len - file_scheme_len;
+                    str_len.saturating_sub(scheme_diff + 2)
+                }
+            } else if cfg!(windows) {
+                // remove scheme: - has posssible \\ for hostname
+                str_len.saturating_sub(self.scheme().len() + 1)
+            } else {
+                // remove scheme://
+                str_len.saturating_sub(self.scheme().len() + 3)
+            };
             return file_url_segments_to_pathbuf(estimated_capacity, host, segments);
         }
         Err(())
@@ -3110,10 +3118,11 @@
     mut segments: str::Split<'_, char>,
 ) -> Result<PathBuf, ()> {
     use percent_encoding::percent_decode_str;
-    let mut string = String::with_capacity(estimated_capacity);
+    let mut string = String::new();
+    string.try_reserve(estimated_capacity).map_err(|_| ())?;
     if let Some(host) = host {
         string.push_str(r"\\");
         string.push_str(host);
     } else {
         let first = segments.next().ok_or(())?;
 
@@ -3123,7 +3132,7 @@
                     return Err(());
                 }
 
                 string.push_str(first);
             }
 
             4 => {
@@ -3135,8 +3144,8 @@
                     return Err(());
                 }
 
                 string.push_str(&first[0..1]);
                 string.push(':');
             }
 
             _ => return Err(()),
@@ -3147,18 +3156,20 @@
         string.push('\\');
 
         // Currently non-unicode windows paths cannot be represented
         match percent_decode_str(segment).decode_utf8() {
             Ok(s) => string.push_str(&s),
             Err(..) => return Err(()),
         }
     }
     // ensure our estimated capacity was good
-    debug_assert!(
-        string.len() <= estimated_capacity,
-        "len: {}, capacity: {}",
-        string.len(),
-        estimated_capacity
-    );
+    if cfg!(test) {
+        debug_assert!(
+            string.len() <= estimated_capacity,
+            "len: {}, capacity: {}",
+            string.len(),
+            estimated_capacity
+        );
+    }
     let path = PathBuf::from(string);
     debug_assert!(
         path.is_absolute(),