3 files changed, 99 insertions, 0 deletions
diff --git a/tests/ui/ineffective_open_options.fixed b/tests/ui/ineffective_open_options.fixed
new file mode 100644
index 00000000000..3af8f3c5aaa
--- /dev/null
+++ b/tests/ui/ineffective_open_options.fixed
@@ -0,0 +1,41 @@
+#![warn(clippy::ineffective_open_options)]
+
+use std::fs::OpenOptions;
+
+fn main() {
+    let file = OpenOptions::new()
+        .create(true)
+         //~ ERROR: unnecessary use of `.write(true)`
+        .append(true)
+        .open("dump.json")
+        .unwrap();
+
+    let file = OpenOptions::new()
+        .create(true)
+        .append(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();
+}
diff --git a/tests/ui/ineffective_open_options.rs b/tests/ui/ineffective_open_options.rs
new file mode 100644
index 00000000000..4eaf6293c40
--- /dev/null
+++ b/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();
+}
diff --git a/tests/ui/ineffective_open_options.stderr b/tests/ui/ineffective_open_options.stderr
new file mode 100644
index 00000000000..7dc5322232c
--- /dev/null
+++ b/tests/ui/ineffective_open_options.stderr
@@ -0,0 +1,17 @@
+error: unnecessary use of `.write(true)` because there is `.append(true)`
+  --> $DIR/ineffective_open_options.rs:8:9
+   |
+LL |         .write(true)
+   |         ^^^^^^^^^^^^ help: remove `.write(true)`
+   |
+   = note: `-D clippy::ineffective-open-options` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::ineffective_open_options)]`
+
+error: unnecessary use of `.write(true)` because there is `.append(true)`
+  --> $DIR/ineffective_open_options.rs:16:9
+   |
+LL |         .write(true)
+   |         ^^^^^^^^^^^^ help: remove `.write(true)`
+
+error: aborting due to 2 previous errors
+