Tests fail when renaming identifiers, etc - rust

Question

I've got a large repo in which I noticed that some tests started failing after I added a dependency to Cargo.toml, despite the dependency never being referenced. I began to investigate, and was able to reproduce the problem consistently in this repo. I'll reproduce the code of the main file here:
mod test {
pub fn b<T>(db: *mut libsqlite3_sys::sqlite3, _: T) {
let rc = unsafe {
libsqlite3_sys::sqlite3_create_function(
db, // db
"x".as_ptr() as _, // zFunction
0, // nArg
0, // eTextRep
std::ptr::null_mut(), // pApp
None, // xFunc
None, // xStep
None, // xFinal
)
};
match rc {
libsqlite3_sys::SQLITE_MISUSE => (),
x => panic!("Wanted SQLITE_MISUSE, got {:?}", x),
}
}
}
#[test]
#[ignore]
fn z() {
format!("{:?}", &[1, 2, 3, 4]);
panic!("not run");
}
#[test]
fn a() {
const FILENAME: &[u8] = b":memory:\0";
let mut db: *mut libsqlite3_sys::sqlite3 = std::ptr::null_mut();
let rc = unsafe { libsqlite3_sys::sqlite3_open(FILENAME.as_ptr() as _, &mut db) };
assert_eq!(rc, libsqlite3_sys::SQLITE_OK);
test::b(db, 0);
}
On my computer, these tests pass, meaning that sqlite3_create_function is returning SQLITE_MISUSE.
$ cargo test --lib --features=static
Finished test [unoptimized + debuginfo] target(s) in 0.52s
Running unittests src/lib.rs (target/debug/deps/sqlite3_ext-5449511dde1f34ef)
running 2 tests
test z ... ignored
test a ... ok
test result: ok. 1 passed; 0 failed; 1 ignored; 0 measured; 0 filtered out; finished in 0.01s
Now, it shouldn't be returning MISUSE, because as far as I can tell everything about this code is valid. However, here's where it gets weird:
If I don't use --features=static, the test fails. Note that nothing references this feature whatsoever.
If I remove the format! line, the test fails. Note that the code is never called.
If I add or remove any dependencies to Cargo.toml, the test fails. None of the changes are referenced anywhere in the code.
If I rename the feature "static" to anything else, the test fails.
If I rename the module "test" to anything else, the test fails.
If I run this code on Linux, the test fails.
I am able to add [features] joke = [] to Cargo.toml, and then I get this behavior:
cargo test --lib --features=joke fails (no MISUSE)
cargo test --lib --features=static passes (MISUSE)
cargo test --lib --features=static,joke fails (no MISUSE)
I am at my wit's end. I am running macOS 10.14.6 (18G9323), rustc 1.61.0 (fe5b13d68 2022-05-18). Any help would be greatly appreciated. I've also uploaded binaries to GitHub for investigation if it helps.

Answer 1

Thanks to #thomcc who responded on the rusqlite Discord:
you’re not passing a nul-terminated string to c for one
This was the issue. In most cases the only problem this caused was that my application-defined function was never removed, but in this particular case it resulted in an SQLITE_MISUSE being returned. Properly converting my &str to CString resolves the issue.