rust/tests/ui/borrowck/borrowck-partial-reinit-4.rs

struct Test;

struct Test2(Option<Test>);

impl Drop for Test {
    fn drop(&mut self) {
        println!("dropping!");
    }
}

impl Drop for Test2 {
    fn drop(&mut self) {}
}

fn stuff() {
    let mut x : (Test2, Test2);
    (x.0).0 = Some(Test); //~ ERROR E0381
}

fn main() {
    stuff()
}
librustc: Forbid partial reinitialization of uninitialized structures or enumerations that implement the `Drop` trait. This breaks code like: struct Struct { f: String, g: String, } impl Drop for Struct { ... } fn main() { let x = Struct { ... }; drop(x); x.f = ...; } Change this code to not create partially-initialized structures. For example: struct Struct { f: String, g: String, } impl Drop for Struct { ... } fn main() { let x = Struct { ... }; drop(x); x = Struct { f: ..., g: ..., } } Closes #18571. [breaking-change] ---- (Joint authorship by pcwalton and Ryman; thanks all!) 2014-11-14 17:14:52 -06:00			`struct Test;`

			`struct Test2(Option<Test>);`

			`impl Drop for Test {`
			`fn drop(&mut self) {`
			`println!("dropping!");`
			`}`
			`}`

			`impl Drop for Test2 {`
			`fn drop(&mut self) {}`
			`}`

			`fn stuff() {`
			`let mut x : (Test2, Test2);`
On partial uninit error point at where we need init When a binding is declared without a value, borrowck verifies that all codepaths have one assignment to them to initialize them fully. If there are any cases where a condition can be met that leaves the binding uninitialized or we attempt to initialize a field of an unitialized binding, we emit E0381. We now look at all the statements that initialize the binding, and use them to explore branching code paths that don't and point at them. If we find no potential places where an assignment to the binding might be missing, we display the spans of all the existing initializers to provide some context. 2022-06-21 13:57:45 -05:00			`(x.0).0 = Some(Test); //~ ERROR E0381`
librustc: Forbid partial reinitialization of uninitialized structures or enumerations that implement the `Drop` trait. This breaks code like: struct Struct { f: String, g: String, } impl Drop for Struct { ... } fn main() { let x = Struct { ... }; drop(x); x.f = ...; } Change this code to not create partially-initialized structures. For example: struct Struct { f: String, g: String, } impl Drop for Struct { ... } fn main() { let x = Struct { ... }; drop(x); x = Struct { f: ..., g: ..., } } Closes #18571. [breaking-change] ---- (Joint authorship by pcwalton and Ryman; thanks all!) 2014-11-14 17:14:52 -06:00			`}`

			`fn main() {`
			`stuff()`
			`}`