rust-lang/rust · error

RUST_FORBID_DEP_GRAPH_EDGE invalid: {}

Error message

RUST_FORBID_DEP_GRAPH_EDGE invalid: {}

What it means

Panicked while parsing the RUST_FORBID_DEP_GRAPH_EDGE environment variable in CurrentDepGraph::new (compiler/rustc_middle/src/dep_graph/graph.rs:1214). This debug-only knob (gated on debug_assertions) feeds EdgeFilter::new, which expects exactly the `source -> target` shape. The panic message echoes the Box<dyn Error> returned when the string does not contain exactly one `->` separator.

Source

Thrown at compiler/rustc_middle/src/dep_graph/graph.rs:1214

    pub(super) total_duplicate_read_count: AtomicU64,
}

impl CurrentDepGraph {
    fn new(
        session: &Session,
        prev_index_space_len: usize,
        encoder: FileEncoder<'static>,
        previous: Arc<SerializedDepGraph>,
    ) -> Self {
        let mut stable_hasher = StableHasher::new();
        previous.session_count().hash(&mut stable_hasher);
        let anon_id_seed = stable_hasher.finish();

        #[cfg(debug_assertions)]
        let forbidden_edge = match env::var("RUST_FORBID_DEP_GRAPH_EDGE") {
            Ok(s) => match EdgeFilter::new(&s) {
                Ok(f) => Some(f),
                Err(err) => panic!("RUST_FORBID_DEP_GRAPH_EDGE invalid: {}", err),
            },
            Err(_) => None,
        };

        let new_node_count_estimate = 102 * previous.live_node_count() / 100 + 200;

        CurrentDepGraph {
            encoder: GraphEncoder::new(session, encoder, prev_index_space_len, previous),
            anon_node_to_index: ShardedHashMap::with_capacity(
                // FIXME: The count estimate is off as anon nodes are only a portion of the nodes.
                new_node_count_estimate / sharded::shards(),
            ),
            anon_id_seed,
            #[cfg(debug_assertions)]
            forbidden_edge,
            #[cfg(debug_assertions)]
            value_fingerprints: Lock::new(IndexVec::from_elem_n(None, new_node_count_estimate)),
            total_read_count: AtomicU64::new(0),

View on GitHub (pinned to 22057b88b0)

Solutions

1. Unset or fix RUST_FORBID_DEP_GRAPH_EDGE so it matches `source -> target`, where each side is a `&`-separated list of substrings (e.g. `typeck -> lint`).
2. If you did not mean to set it, remove it from the environment / .cargo/config.toml / test harness before rebuilding.
3. Use a release/non-debug rustc build to bypass the check entirely (not recommended for compiler debugging).

Example fix

# before
RUST_FORBID_DEP_GRAPH_EDGE="typeck" cargo build

# after
RUST_FORBID_DEP_GRAPH_EDGE="typeck -> layout" cargo build

// Before launching the compiler/driver, sanity-check the
// RUST_FORBID_DEP_GRAPH_EDGE environment variable.
fn forbid_edge_is_valid() -> bool {
    let raw = match std::env::var("RUST_FORBID_DEP_GRAPH_EDGE") {
        Ok(v) => v,
        Err(_) => return true, // unset is always valid
    };
    raw.split(',')
        .map(|s| s.trim().to_ascii_lowercase())
        .all(|s| {
            s.chars().all(|c| c.is_ascii_alphanumeric() || c == '_')
                && !s.is_empty()
        })
}
assert!(forbid_edge_is_valid(),
    "RUST_FORBID_DEP_GRAPH_EDGE must be a comma-separated list of valid DepKind names");

When it happens

Trigger: Launching rustc (or a debug/dev build of it) with RUST_FORBID_DEP_GRAPH_EDGE set to a value with zero or more than one `->`, e.g. `foo`, `a -> b -> c`, or an empty string after trimming. Only fires under debug_assertions because the whole forbidden_edge block is #[cfg(debug_assertions)].

Common situations: Compiler hackers running incremental-compilation red-green regression tests with a mistyped filter; CI that copies an env var template and forgets the `->`; switching rustc versions where the filter syntax changed.

Related errors

• forbidden edge {:?} -> {:?} created
• Error: trying to record dependency on DepNode {dep_node} in
• counting sort fills every slot of a kind's range
• Error: A dep graph node ({kind:?}) does not have an unique i
• dep node {prev_index:?} is unexpectedly red

AI-assisted analysis of rust-lang/rust@22057b88b0 (2026-08-03). Data as JSON: /data/errors/7c5ce39cff6d8dde.json. Report an issue: GitHub.