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Improve ICE message for forbidden dep-graph reads. #124252

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merged 2 commits into from
Apr 23, 2024
Merged

Improve ICE message for forbidden dep-graph reads. #124252

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c373ec0
Improve ICE message for forbidden dep-graph reads.
michaelwoerister Apr 22, 2024
6146a51
Add more context to the forbidden dep-graph read ICE error message.
michaelwoerister Apr 22, 2024
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41 changes: 40 additions & 1 deletion compiler/rustc_query_system/src/dep_graph/graph.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -459,7 +459,8 @@ impl<D: Deps> DepGraph<D> {
}
TaskDepsRef::Ignore => return,
TaskDepsRef::Forbid => {
panic!("Illegal read of: {dep_node_index:?}")
// Reading is forbidden in this context. ICE with a useful error message.
panic_on_forbidden_read(data, dep_node_index)
}
};
let task_deps = &mut *task_deps;
Expand Down Expand Up @@ -1366,3 +1367,41 @@ pub(crate) fn print_markframe_trace<D: Deps>(graph: &DepGraph<D>, frame: Option<

eprintln!("end of try_mark_green dep node stack");
}

#[cold]
#[inline(never)]
fn panic_on_forbidden_read<D: Deps>(data: &DepGraphData<D>, dep_node_index: DepNodeIndex) -> ! {
// We have to do an expensive reverse-lookup of the DepNode that
// corresponds to `dep_node_index`, but that's OK since we are about
// to ICE anyway.
let mut dep_node = None;

// First try to find the dep node among those that already existed in the
// previous session
for (prev_index, index) in data.current.prev_index_to_index.lock().iter_enumerated() {
if index == &Some(dep_node_index) {
dep_node = Some(data.previous.index_to_node(prev_index));
break;
}
}

if dep_node.is_none() {
// Try to find it among the new nodes
for shard in data.current.new_node_to_index.lock_shards() {
if let Some((node, _)) = shard.iter().find(|(_, index)| **index == dep_node_index) {
dep_node = Some(*node);
break;
}
}
}

let dep_node = dep_node.map_or_else(
|| format!("with index {:?}", dep_node_index),
|dep_node| format!("`{:?}`", dep_node),
);

panic!(
"Error: trying to record dependency on DepNode {dep_node} in a \
context that does not allow it (e.g. during query deserialization)."
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@RalfJung RalfJung Apr 22, 2024 •
edited
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FWIW, as someone who knows nothing about the query/incremental system, I still don't know that "record dependency" is the same as "invoke query". Or maybe it's not the same, but the explanation you gave me that I actually understood was "you invoked a query in a context that does not allow it". But maybe there are cases where saying "invoked a query" here would be wrong?

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Good point. Invoking a query is only of several ways of recording something in the dependency graph, but it is by far the most common. I'll update the error message.

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Is the new message better?

)
}
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