diff options
Diffstat (limited to 'src/tools/clippy/tests/ui/collection_is_never_read.rs')
-rw-r--r-- | src/tools/clippy/tests/ui/collection_is_never_read.rs | 190 |
1 files changed, 190 insertions, 0 deletions
diff --git a/src/tools/clippy/tests/ui/collection_is_never_read.rs b/src/tools/clippy/tests/ui/collection_is_never_read.rs new file mode 100644 index 000000000..01259a983 --- /dev/null +++ b/src/tools/clippy/tests/ui/collection_is_never_read.rs @@ -0,0 +1,190 @@ +#![allow(unused)] +#![warn(clippy::collection_is_never_read)] + +use std::collections::{HashMap, HashSet}; + +fn main() {} + +fn not_a_collection() { + // TODO: Expand `collection_is_never_read` beyond collections? + let mut x = 10; // Ok + x += 1; +} + +fn no_access_at_all() { + // Other lints should catch this. + let x = vec![1, 2, 3]; // Ok +} + +fn write_without_read() { + // The main use case for `collection_is_never_read`. + let mut x = HashMap::new(); // WARNING + x.insert(1, 2); +} + +fn read_without_write() { + let mut x = vec![1, 2, 3]; // Ok + let _ = x.len(); +} + +fn write_and_read() { + let mut x = vec![1, 2, 3]; // Ok + x.push(4); + let _ = x.len(); +} + +fn write_after_read() { + // TODO: Warn here, but this requires more extensive data flow analysis. + let mut x = vec![1, 2, 3]; // Ok + let _ = x.len(); + x.push(4); // Pointless +} + +fn write_before_reassign() { + // TODO: Warn here, but this requires more extensive data flow analysis. + let mut x = HashMap::new(); // Ok + x.insert(1, 2); // Pointless + x = HashMap::new(); + let _ = x.len(); +} + +fn read_in_closure() { + let mut x = HashMap::new(); // Ok + x.insert(1, 2); + let _ = || { + let _ = x.len(); + }; +} + +fn write_in_closure() { + let mut x = vec![1, 2, 3]; // WARNING + let _ = || { + x.push(4); + }; +} + +fn read_in_format() { + let mut x = HashMap::new(); // Ok + x.insert(1, 2); + format!("{x:?}"); +} + +fn shadowing_1() { + let x = HashMap::<usize, usize>::new(); // Ok + let _ = x.len(); + let mut x = HashMap::new(); // WARNING + x.insert(1, 2); +} + +fn shadowing_2() { + let mut x = HashMap::new(); // WARNING + x.insert(1, 2); + let x = HashMap::<usize, usize>::new(); // Ok + let _ = x.len(); +} + +#[allow(clippy::let_unit_value)] +fn fake_read_1() { + let mut x = vec![1, 2, 3]; // WARNING + x.reverse(); + let _: () = x.clear(); +} + +fn fake_read_2() { + let mut x = vec![1, 2, 3]; // WARNING + x.reverse(); + println!("{:?}", x.push(5)); +} + +fn assignment() { + let mut x = vec![1, 2, 3]; // WARNING + let y = vec![4, 5, 6]; // Ok + x = y; +} + +#[allow(clippy::self_assignment)] +fn self_assignment() { + let mut x = vec![1, 2, 3]; // WARNING + x = x; +} + +fn method_argument_but_not_target() { + struct MyStruct; + impl MyStruct { + fn my_method(&self, _argument: &[usize]) {} + } + let my_struct = MyStruct; + + let mut x = vec![1, 2, 3]; // Ok + x.reverse(); + my_struct.my_method(&x); +} + +fn insert_is_not_a_read() { + let mut x = HashSet::new(); // WARNING + x.insert(5); +} + +fn insert_is_a_read() { + let mut x = HashSet::new(); // Ok + if x.insert(5) { + println!("5 was inserted"); + } +} + +fn not_read_if_return_value_not_used() { + // `is_empty` does not modify the set, so it's a query. But since the return value is not used, the + // lint does not consider it a read here. + let x = vec![1, 2, 3]; // WARNING + x.is_empty(); +} + +fn extension_traits() { + trait VecExt<T> { + fn method_with_side_effect(&self); + fn method_without_side_effect(&self); + } + + impl<T> VecExt<T> for Vec<T> { + fn method_with_side_effect(&self) { + println!("my length: {}", self.len()); + } + fn method_without_side_effect(&self) {} + } + + let x = vec![1, 2, 3]; // Ok + x.method_with_side_effect(); + + let y = vec![1, 2, 3]; // Ok (false negative) + y.method_without_side_effect(); +} + +fn function_argument() { + #[allow(clippy::ptr_arg)] + fn foo<T>(v: &Vec<T>) -> usize { + v.len() + } + + let x = vec![1, 2, 3]; // Ok + foo(&x); +} + +fn string() { + // Do lint (write without read) + let mut s = String::new(); + s.push_str("Hello, World!"); + + // Do not lint (read without write) + let mut s = String::from("Hello, World!"); + let _ = s.len(); + + // Do not lint (write and read) + let mut s = String::from("Hello, World!"); + s.push_str("foo, bar"); + let _ = s.len(); + + // Do lint the first line, but not the second + let mut s = String::from("Hello, World!"); + let t = String::from("foo, bar"); + s = t; +} |