1 files changed, 43 insertions, 0 deletions
diff --git a/src/tools/clippy/tests/ui/write_literal.rs b/src/tools/clippy/tests/ui/write_literal.rs
new file mode 100644
index 00000000000..d8205c5eb67
--- /dev/null
+++ b/src/tools/clippy/tests/ui/write_literal.rs
@@ -0,0 +1,43 @@
+#![allow(unused_must_use)]
+#![warn(clippy::write_literal)]
+
+use std::io::Write;
+
+fn main() {
+    let mut v = Vec::new();
+
+    // these should be fine
+    write!(&mut v, "Hello");
+    writeln!(&mut v, "Hello");
+    let world = "world";
+    writeln!(&mut v, "Hello {}", world);
+    writeln!(&mut v, "Hello {world}", world = world);
+    writeln!(&mut v, "3 in hex is {:X}", 3);
+    writeln!(&mut v, "2 + 1 = {:.4}", 3);
+    writeln!(&mut v, "2 + 1 = {:5.4}", 3);
+    writeln!(&mut v, "Debug test {:?}", "hello, world");
+    writeln!(&mut v, "{0:8} {1:>8}", "hello", "world");
+    writeln!(&mut v, "{1:8} {0:>8}", "hello", "world");
+    writeln!(&mut v, "{foo:8} {bar:>8}", foo = "hello", bar = "world");
+    writeln!(&mut v, "{bar:8} {foo:>8}", foo = "hello", bar = "world");
+    writeln!(&mut v, "{number:>width$}", number = 1, width = 6);
+    writeln!(&mut v, "{number:>0width$}", number = 1, width = 6);
+
+    // these should throw warnings
+    writeln!(&mut v, "{} of {:b} people know binary, the other half doesn't", 1, 2);
+    write!(&mut v, "Hello {}", "world");
+    writeln!(&mut v, "Hello {} {}", world, "world");
+    writeln!(&mut v, "Hello {}", "world");
+    writeln!(&mut v, "10 / 4 is {}", 2.5);
+    writeln!(&mut v, "2 + 1 = {}", 3);
+
+    // positional args don't change the fact
+    // that we're using a literal -- this should
+    // throw a warning
+    writeln!(&mut v, "{0} {1}", "hello", "world");
+    writeln!(&mut v, "{1} {0}", "hello", "world");
+
+    // named args shouldn't change anything either
+    writeln!(&mut v, "{foo} {bar}", foo = "hello", bar = "world");
+    writeln!(&mut v, "{bar} {foo}", foo = "hello", bar = "world");
+}