fix not to break relative path link (#4042)

Author: rchaser53

rustfmt-core/rustfmt-lib/src/string.rs

@@ -169,6 +169,7 @@ fn detect_url(s: &[&str], index: usize) -> Option<usize> {
         || split.contains("http://")
         || split.contains("ftp://")
         || split.contains("file://")
+        || split.contains("./")
     {
         match s[index..].iter().position(|g| is_whitespace(g)) {
             Some(pos) => Some(index + pos - 1),

rustfmt-core/rustfmt-lib/tests/target/issue-4023.rs

@@ -0,0 +1,12 @@
+// rustfmt-max_width: 100
+// rustfmt-wrap_comments: true
+// rustfmt-comment_width: 80
+// rustfmt-normalize_comments: true
+// rustfmt-unstable_features: true
+
+struct Test {
+    /// [`MANAGE_MESSAGES`]: ../permissions/struct.Permissions.html#associatedconstant.MANAGE_MESSAGES
+    /// [`MANAGE_CHANNEL`]: ./permissions/struct.Permissions.html#associatedconstant.MANAGE_CHANNEL
+    #[serde(default, rename = "rate_limit_per_user")]
+    pub rate_limit: u16,
+}