In Rust, calling Vec::set_len(new_len) directly after allocating or reserving memory using Vec::with_capacity(),
Vec::new(), Vec::default(), or Vec::reserve() can lead to the creation of a Vec with uninitialized
elements. This is problematic because most safe Rust operations assume initialized data. Using uninitialized data can result in undefined behavior,
including memory corruption and unexpected program crashes.
This rule detects instances where Vec::set_len() is called directly after allocating or reserving memory with
Vec::with_capacity(), Vec::new(), Vec::default(), or Vec::reserve(), without any prior
initialization of the vector’s elements. The rule performs a local analysis and only checks for these calls within adjacent statements.
Code examples
Noncompliant code example
fn f(reader: &mut dyn std::io::Read) {
let mut vec: Vec<u8> = Vec::with_capacity(1000);
unsafe { vec.set_len(1000); } // Noncompliant: Uninitialized vector
reader.read_exact(&mut vec).unwrap(); // Undefined behavior!
}
Compliant solution
fn f(reader: &mut dyn std::io::Read) {
let mut vec: Vec<u8> = vec![0; 1000]; // Properly initialized with zeros
reader.read_exact(&mut vec).unwrap(); // Safe to use
}
