resolve #4542 by removing machine applicable suggestion

Author: JoshMcguigan

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_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();
+}

tests/ui/explicit_write_non_rustfix.stderr

@@ -0,0 +1,16 @@
+error[E0599]: no method named `write_fmt` found for type `std::io::Stderr` in the current scope
+  --> $DIR/explicit_write_non_rustfix.rs:6:5
+   |
+LL |     writeln!(std::io::stderr(), "foo {}", bar).unwrap();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ method not found in `std::io::Stderr`
+   |
+   = help: items from traits can only be used if the trait is in scope
+   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+help: the following trait is implemented but not in scope, perhaps add a `use` for it:
+   |
+LL | use std::io::Write;
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0599`.