fix: do not wrap reference-style doc links

Prevents wrap_comments from incorrectly wrapping reference-style doc
links.

Author: domodwyer

src/comment.rs

@@ -3,6 +3,8 @@
 use std::{self, borrow::Cow, iter};
 
 use itertools::{multipeek, MultiPeek};
+use lazy_static::lazy_static;
+use regex::Regex;
 use rustc_span::Span;
 
 use crate::config::Config;
@@ -15,6 +17,17 @@ use crate::utils::{
 };
 use crate::{ErrorKind, FormattingError};
 
+lazy_static! {
+    /// A regex matching reference doc links.
+    ///
+    /// ```markdown
+    /// /// An [example].
+    /// ///
+    /// /// [example]: this::is::a::link
+    /// ```
+    static ref REFERENCE_LINK_URL: Regex = Regex::new(r"^\[.+\]\s?:").unwrap();
+}
+
 fn is_custom_comment(comment: &str) -> bool {
     if !comment.starts_with("//") {
         false
@@ -842,7 +855,11 @@ fn trim_custom_comment_prefix(s: &str) -> String {
 /// Returns `true` if the given string MAY include URLs or alike.
 fn has_url(s: &str) -> bool {
     // This function may return false positive, but should get its job done in most cases.
-    s.contains("https://") || s.contains("http://") || s.contains("ftp://") || s.contains("file://")
+    s.contains("https://")
+        || s.contains("http://")
+        || s.contains("ftp://")
+        || s.contains("file://")
+        || REFERENCE_LINK_URL.is_match(s)
 }
 
 /// Given the span, rewrite the missing comment inside it if available.

tests/target/issue-5095.rs

@@ -0,0 +1,27 @@
+// rustfmt-wrap_comments: true
+
+pub mod a_long_name {
+    pub mod b_long_name {
+        pub mod c_long_name {
+            pub mod d_long_name {
+                pub mod e_long_name {
+                    pub struct Bananas;
+                    impl Bananas {
+                        pub fn fantastic() {}
+                    }
+
+                    pub mod f_long_name {
+                        pub struct Apples;
+                    }
+                }
+            }
+        }
+    }
+}
+
+/// Check out [my other struct] ([`Bananas`]) and [the method it has].
+///
+/// [my other struct]: a_long_name::b_long_name::c_long_name::d_long_name::e_long_name::f_long_name::Apples
+/// [`Bananas`]: a_long_name::b_long_name::c_long_name::d_long_name::e_long_name::Bananas::fantastic()
+/// [the method it has]: a_long_name::b_long_name::c_long_name::d_long_name::e_long_name::Bananas::fantastic()
+pub struct A;