borrowck unsoundness

[emberian]

fn read_lines_borrowed() -> ~[&str] {
    let rawLines: ~[~str] = ~[~"foo  ", ~"  bar"];
    rawLines.iter().map(|l| l.trim()).collect()
}

fn main() {
    println!("{}", read_lines_borrowed());
}

read_lines_borrowed is not rejected. but the value it returns cannot possibly be valid, since rawLines is going to be free'd after it returns, leaving the collected references dangling.

[emberian]

cc @nikomatsakis @pcwalton @brson @alexcrichton @pnkfelix

[emberian]

(specifically the only valid lifetime should be 'static)

[emberian]

A longer example, which this is extracted from, exhibits memory unsafety: https://gist.github.com/anonymous/10601934

[alexcrichton]

This is likely a dupe of #12223, but I'm not familiar enough with the code to say for certain.

[emberian]

They do appear similar.

[flaper87]

I agree with @alexcrichton I think this is a dupe of #13497

mind if I copy this example in that bug and close this one? The other bug has already been triaged and prioritized.

[emberian]

I'm not convinced this is actually a dupe, the other seems to have to do
with dropping a value that ought not to be, whereas this one is a lifetime
mismatch (doesn't live long enough). Not sure.

On Mon, Apr 14, 2014 at 5:00 PM, Flavio Percoco Premoli <
notifications@github.com> wrote:

I agree with @alexcrichton https://github.com/alexcrichton I think this
is a dupe of #13497 #13497

mind if I copy this example in that bug and close this one? The other bug
has already been triaged and prioritized.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/13497#issuecomment-40417480
.

http://octayn.net/

[nikomatsakis]

I'll try to investigate today.

[jfager]

The current-rust translations of this seems to be correctly rejected:

With:

fn read_lines_borrowed() -> Vec<&str> {
    let rawLines: Vec<String> = vec!["foo  ".to_string(), "  bar".to_string()];
    rawLines.iter().map(|l| l.as_slice().trim()).collect()
}

I get:

$ rustc r13497.rs 
r13497.rs:1:33: 1:37 error: missing lifetime specifier [E0106]
r13497.rs:1 fn read_lines_borrowed() -> Vec<&str> {

And with:

fn read_lines_borrowed<'a>() -> Vec<&'a str> {
    let rawLines: Vec<String> = vec!["foo  ".to_string(), "  bar".to_string()];
    rawLines.iter().map(|l| l.as_slice().trim()).collect()
}

I get:

$ rustc r13497.rs 
r13497.rs:3:5: 3:13 error: `rawLines` does not live long enough
r13497.rs:3     rawLines.iter().map(|l| l.as_slice().trim()).collect()
                ^~~~~~~~
r13497.rs:1:46: 4:2 note: reference must be valid for the lifetime 'a as defined on the block at 1:45...
r13497.rs:1 fn read_lines_borrowed<'a>() -> Vec<&'a str> {
r13497.rs:2     let rawLines: Vec<String> = vec!["foo  ".to_string(), "  bar".to_string()];
r13497.rs:3     rawLines.iter().map(|l| l.as_slice().trim()).collect()
r13497.rs:4 }
r13497.rs:1:46: 4:2 note: ...but borrowed value is only valid for the block at 1:45
r13497.rs:1 fn read_lines_borrowed<'a>() -> Vec<&'a str> {
r13497.rs:2     let rawLines: Vec<String> = vec!["foo  ".to_string(), "  bar".to_string()];
r13497.rs:3     rawLines.iter().map(|l| l.as_slice().trim()).collect()
r13497.rs:4 }
error: aborting due to previous error

[alexcrichton]

Thanks @jfager! Flagging as needstest.