Reached the recursion limit while instantiating (closure) #137784
Description
I tried this code:
pub fn search( root: bool, at: &mut serde_json::Value, needle: &serde_json::Value, handle_end_found_obj: &mut impl FnMut() -> SearchRes, handle_end_found_arr: &mut impl FnMut() -> SearchRes, handle_end_root: impl FnOnce() -> SearchRes, ) { if root && at == needle { match handle_end_root() { SearchRes::Replace(value) => *at = value, SearchRes::Delete => *at = serde_json::Value::Null, } } else { match &mut *at { serde_json::Value::Array(values) => { let mut i = 0; while i < values.len() { if values[i] == *needle { match handle_end_found_arr() { SearchRes::Delete => { values.remove(i); }, SearchRes::Replace(v) => { values[i] = v; i += 1; }, } } else { search( false, &mut values[i], &*needle, &mut *handle_end_found_obj, &mut *handle_end_found_arr, || unreachable!(), ); i += 1; } } }, serde_json::Value::Object(map) => { for k in map.keys().cloned().collect::<Vec<_>>() { if map[&k] == *needle { match handle_end_found_obj() { SearchRes::Replace(value) => { map.insert(k, value); }, SearchRes::Delete => { map.remove(&k); }, } } else { search( false, &mut map[&k], &*needle, &mut *handle_end_found_obj, &mut *handle_end_found_arr, || unreachable!(), ); } } }, _ => { }, } } }I expected to see this happen: Compile success
Instead, this happened: Compile fails with the error:
Compiling hammer-of-json v0.1.0 (/mnt/home-dev/r/jsonhammer/source) error: reached the recursion limit while instantiating `search::<{closure@src/search_delete.rs:9:39: 9:41}, {closure@src/search_delete.rs:9:66: 9:68}, {closure@src/utils.rs:210:29: 210:31}>` --> src/utils.rs:204:25 | 204 | / search( 205 | | false, 206 | | &mut values[i], 207 | | &*needle, ... | 210 | | || unreachable!(), 211 | | ); | |_________________________^ | note: `search` defined here --> src/utils.rs:175:1 | 175 | / pub fn search( 176 | | root: bool, 177 | | at: &mut serde_json::Value, 178 | | needle: &serde_json::Value, ... | 181 | | handle_end_root: impl FnOnce() -> SearchRes, 182 | | ) { | |_^ error: could not compile `hammer-of-json` (bin "hammer-of-json") due to 1 previous error Exception: cargo exited with 101 Meta
rustc --version --verbose:
rustc 1.87.0-nightly (794c12416 2025-02-21) Setting the recursion limit to 1024 didn't help.
I worked around the issue by defining
fn nil_handle_end() -> SearchRes { unreachable!(); } then replacing || unreachable!() with nil_handle_end, so I think it's probably related to closures.
This may be "as designed" so feel free to close, but from a user perspective it was fairly unexpected and the line just pointed to a closure with no real indication of why that was causing recursion or anything that would indicate how to solve the issue.