resolve rust-lang#4542 by removing machine applicable suggestion

clippy_lints/src/explicit_write.rs

@@ -140,7 +140,8 @@ fn write_output_string(write_args: &HirVec<Expr>) -> Option<String> {
         if output_args.len() > 0;
         if let ExprKind::AddrOf(_, ref output_string_expr) = output_args[0].node;
         if let ExprKind::Array(ref string_exprs) = output_string_expr.node;
-        if string_exprs.len() > 0;
+        // we only want to provide an automatic suggestion for simple (non-format) strings
+        if string_exprs.len() == 1;
         if let ExprKind::Lit(ref lit) = string_exprs[0].node;
         if let LitKind::Str(ref write_output, _) = lit.node;
         then {

tests/ui/explicit_write.fixed

@@ -1,5 +1,5 @@
 // run-rustfix
-#![allow(unused_imports)]
+#![allow(unused_imports, clippy::blacklisted_name)]
 #![warn(clippy::explicit_write)]
 
 fn stdout() -> String {
@@ -24,6 +24,10 @@ fn main() {
         // including newlines
         println!("test\ntest");
         eprintln!("test\ntest");
+
+        // including formatting
+        let bar = "bar";
+        writeln!(std::io::stderr(), "foo {}", bar).unwrap();
     }
     // these should not warn, different destination
     {

tests/ui/explicit_write.stderr

@@ -48,5 +48,11 @@ error: use of `writeln!(stderr(), ...).unwrap()`
 LL |         writeln!(std::io::stderr(), "test/ntest").unwrap();
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `eprintln!("test/ntest")`
 
-error: aborting due to 8 previous errors
+error: use of `writeln!(stderr(), ...).unwrap()`. Consider using `eprintln!` instead
+  --> $DIR/explicit_write.rs:30:9
+   |
+LL |         writeln!(std::io::stderr(), "foo {}", bar).unwrap();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 9 previous errors
 

tests/ui/explicit_write_non_rustfix.rs

@@ -0,0 +1,7 @@
+#![allow(unused_imports, clippy::blacklisted_name)]
+#![warn(clippy::explicit_write)]
+
+fn main() {
+    let bar = "bar";
+    writeln!(std::io::stderr(), "foo {}", bar).unwrap();
+}