1 files changed, 41 insertions, 0 deletions
diff --git a/src/tools/clippy/tests/ui/ineffective_open_options.rs b/src/tools/clippy/tests/ui/ineffective_open_options.rs
new file mode 100644
index 000000000..4eaf6293c
--- /dev/null
+++ b/src/tools/clippy/tests/ui/ineffective_open_options.rs
@@ -0,0 +1,41 @@
+#![warn(clippy::ineffective_open_options)]
+
+use std::fs::OpenOptions;
+
+fn main() {
+    let file = OpenOptions::new()
+        .create(true)
+        .write(true) //~ ERROR: unnecessary use of `.write(true)`
+        .append(true)
+        .open("dump.json")
+        .unwrap();
+
+    let file = OpenOptions::new()
+        .create(true)
+        .append(true)
+        .write(true) //~ ERROR: unnecessary use of `.write(true)`
+        .open("dump.json")
+        .unwrap();
+
+    // All the next calls are ok.
+    let file = OpenOptions::new()
+        .create(true)
+        .write(false)
+        .append(true)
+        .open("dump.json")
+        .unwrap();
+    let file = OpenOptions::new()
+        .create(true)
+        .write(true)
+        .append(false)
+        .open("dump.json")
+        .unwrap();
+    let file = OpenOptions::new()
+        .create(true)
+        .write(false)
+        .append(false)
+        .open("dump.json")
+        .unwrap();
+    let file = OpenOptions::new().create(true).append(true).open("dump.json").unwrap();
+    let file = OpenOptions::new().create(true).write(true).open("dump.json").unwrap();
+}