Merge pull request #2131 from devonhollowood/suggest-print

Suggest print

tests/ui/explicit_write.rs

@@ -0,0 +1,46 @@
+#![warn(explicit_write)]
+
+
+fn stdout() -> String {
+    String::new()
+}
+
+fn stderr() -> String {
+    String::new()
+}
+
+fn main() {
+    // these should warn
+    {
+        use std::io::Write;
+        write!(std::io::stdout(), "test").unwrap();
+        write!(std::io::stderr(), "test").unwrap();
+        writeln!(std::io::stdout(), "test").unwrap();
+        writeln!(std::io::stderr(), "test").unwrap();
+        std::io::stdout().write_fmt(format_args!("test")).unwrap();
+        std::io::stderr().write_fmt(format_args!("test")).unwrap();
+    }
+    // these should not warn, different destination
+    {
+        use std::fmt::Write;
+        let mut s = String::new();
+        write!(s, "test").unwrap();
+        write!(s, "test").unwrap();
+        writeln!(s, "test").unwrap();
+        writeln!(s, "test").unwrap();
+        s.write_fmt(format_args!("test")).unwrap();
+        s.write_fmt(format_args!("test")).unwrap();
+        write!(stdout(), "test").unwrap();
+        write!(stderr(), "test").unwrap();
+        writeln!(stdout(), "test").unwrap();
+        writeln!(stderr(), "test").unwrap();
+        stdout().write_fmt(format_args!("test")).unwrap();
+        stderr().write_fmt(format_args!("test")).unwrap();
+    }
+    // these should not warn, no unwrap
+    {
+        use std::io::Write;
+        std::io::stdout().write_fmt(format_args!("test")).expect("no stdout");
+        std::io::stderr().write_fmt(format_args!("test")).expect("no stderr");
+    }
+}

tests/ui/explicit_write.stderr

@@ -0,0 +1,38 @@
+error: use of `write!(stdout(), ...).unwrap()`. Consider using `print!` instead
+  --> $DIR/explicit_write.rs:16:9
+   |
+16 |         write!(std::io::stdout(), "test").unwrap();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D explicit-write` implied by `-D warnings`
+
+error: use of `write!(stderr(), ...).unwrap()`. Consider using `eprint!` instead
+  --> $DIR/explicit_write.rs:17:9
+   |
+17 |         write!(std::io::stderr(), "test").unwrap();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: use of `writeln!(stdout(), ...).unwrap()`. Consider using `println!` instead
+  --> $DIR/explicit_write.rs:18:9
+   |
+18 |         writeln!(std::io::stdout(), "test").unwrap();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: use of `writeln!(stderr(), ...).unwrap()`. Consider using `eprintln!` instead
+  --> $DIR/explicit_write.rs:19:9
+   |
+19 |         writeln!(std::io::stderr(), "test").unwrap();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: use of `stdout().write_fmt(...).unwrap()`. Consider using `print!` instead
+  --> $DIR/explicit_write.rs:20:9
+   |
+20 |         std::io::stdout().write_fmt(format_args!("test")).unwrap();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: use of `stderr().write_fmt(...).unwrap()`. Consider using `eprint!` instead
+  --> $DIR/explicit_write.rs:21:9
+   |
+21 |         std::io::stderr().write_fmt(format_args!("test")).unwrap();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+