wip fix for rust-lang#4208

Author: matthiaskrgr

clippy_lints/src/write.rs

@@ -200,7 +200,7 @@ impl EarlyLintPass for Write {
         } else if mac.node.path == sym!(print) {
             span_lint(cx, PRINT_STDOUT, mac.span, "use of `print!`");
             if let (Some(fmt_str), _) = check_tts(cx, &mac.node.tts, false) {
-                if check_newlines(&fmt_str) {
+                if terminating_newline(&fmt_str) {
                     span_lint_and_then(
                         cx,
                         PRINT_WITH_NEWLINE,
@@ -221,7 +221,7 @@ impl EarlyLintPass for Write {
             }
         } else if mac.node.path == sym!(write) {
             if let (Some(fmt_str), _) = check_tts(cx, &mac.node.tts, true) {
-                if check_newlines(&fmt_str) {
+                if terminating_newline(&fmt_str) {
                     span_lint_and_then(
                         cx,
                         WRITE_WITH_NEWLINE,
@@ -439,10 +439,15 @@ fn check_tts<'a>(cx: &EarlyContext<'a>, tts: &TokenStream, is_write: bool) -> (O
 /// Checks if the format string constains a single newline that terminates it.
 ///
 /// Literal and escaped newlines are both checked (only literal for raw strings).
-fn check_newlines(fmt_str: &FmtStr) -> bool {
+fn terminating_newline(fmt_str: &FmtStr) -> bool {
     let s = &fmt_str.contents;
 
     if s.ends_with('\n') {
+        let last_but_one = s.chars().rev().nth(1);
+        if last_but_one == Some('\r') {
+            return false
+        }
+   
         return true;
     } else if let StrStyle::Raw(_) = fmt_str.style {
         return false;

tests/ui/write_with_newline.rs

@@ -29,6 +29,8 @@ fn main() {
     write!(&mut v, "Hello {} {}\n\n", "world", "#2");
     writeln!(&mut v, "\ndon't\nwarn\nfor\nmultiple\nnewlines\n"); // #3126
     writeln!(&mut v, "\nbla\n\n"); // #3126
+    write!(&mut v, "\r\n"); // 4208
+    write!(&mut v, "foobar\r\n"); // 4208
 
     // Escaping
     write!(&mut v, "\\n"); // #3514
@@ -49,4 +51,5 @@ fn main() {
         r"
 "
     );
+
 }