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// Copyright 2023 Oxide Computer Company
use std::{
collections::{BTreeMap, BTreeSet},
ops::Range,
};
use crate::{
type_entry::{
TypeEntry, TypeEntryDetails, TypeEntryEnum, TypeEntryNewtype, TypeEntryStruct,
VariantDetails,
},
TypeId, TypeSpace,
};
impl TypeSpace {
/// We need to root out any containment cycles, breaking them by inserting
/// a `Box` type. Our choice of *where* to break cycles is more arbitrary
/// than optimal, but is well beyond sufficient.
pub fn break_cycles(&mut self, range: Range<u64>) {
enum Node {
Start {
type_id: TypeId,
},
Processing {
type_id: TypeId,
children_ids: Vec<TypeId>,
},
}
let mut visited = BTreeSet::<TypeId>::new();
for id in range {
let type_id = TypeId(id);
// This isn't strictly necessary, but we'll short-circuit some work
// by checking this right away.
if visited.contains(&type_id) {
continue;
}
let mut active = BTreeSet::<TypeId>::new();
let mut stack = Vec::<Node>::new();
active.insert(type_id.clone());
stack.push(Node::Start { type_id });
while let Some(top) = stack.last_mut() {
match top {
// Skip right to the end since we've already seen this type.
Node::Start { type_id } if visited.contains(type_id) => {
assert!(active.contains(type_id));
let type_id = type_id.clone();
*top = Node::Processing {
type_id,
children_ids: Vec::new(),
};
}
// Break any immediate cycles and queue up this type for
// descent into its child types.
Node::Start { type_id } => {
assert!(active.contains(type_id));
visited.insert(type_id.clone());
// Determine which child types form cycles--and
// therefore need to be snipped--and the rest--into
// which we should descend. We make this its own block
// to clarify the lifetime of the exclusive reference
// to the type. We don't really *need* to have an
// exclusive reference here, but there's no point in
// writing `get_child_ids` again for shared references.
let (snip, descend) = {
let type_entry = self.id_to_entry.get_mut(type_id).unwrap();
let child_ids = get_child_ids(type_entry)
.into_iter()
.map(|child_id| child_id.clone());
// If the child type is in active then we've found
// a cycle (otherwise we'll descend).
child_ids.partition::<Vec<_>, _>(|child_id| active.contains(child_id))
};
// Note that while `snip` might contain duplicates,
// `id_to_box` is idempotent insofar as the same input
// TypeId will result in the same output TypeId. Ergo
// the resulting pairs from which we construct the
// mapping would contain exact duplicates; it would not
// contain two values associated with the same key.
let replace = snip
.into_iter()
.map(|type_id| {
let box_id = self.id_to_box(&type_id);
(type_id, box_id)
})
.collect::<BTreeMap<_, _>>();
// Break any cycles by reassigning the child type to a box.
let type_entry = self.id_to_entry.get_mut(type_id).unwrap();
let child_ids = get_child_ids(type_entry);
for child_id in child_ids {
if let Some(replace_id) = replace.get(child_id) {
*child_id = replace_id.clone();
}
}
// Descend into child types.
let node = Node::Processing {
type_id: type_id.clone(),
children_ids: descend,
};
*top = node;
}
// If there are children left, push the next child onto the
// stack. If there are none left, pop this type.
Node::Processing {
type_id,
children_ids,
} => {
if let Some(type_id) = children_ids.pop() {
// Descend into the next child node.
active.insert(type_id.clone());
stack.push(Node::Start { type_id });
} else {
// All done; remove the item from the active list
// and stack.
active.remove(type_id);
let _ = stack.pop();
}
}
}
}
}
}
}
/// For types that could potentially participate in a cycle, return a list of
/// mutable references to the child types.
fn get_child_ids(type_entry: &mut TypeEntry) -> Vec<&mut TypeId> {
match &mut type_entry.details {
TypeEntryDetails::Enum(TypeEntryEnum { variants, .. }) => variants
.iter_mut()
.flat_map(|variant| match &mut variant.details {
VariantDetails::Simple => Vec::new(),
VariantDetails::Item(type_id) => vec![type_id],
VariantDetails::Tuple(type_ids) => type_ids.iter_mut().collect(),
VariantDetails::Struct(properties) => properties
.iter_mut()
.map(|prop| &mut prop.type_id)
.collect(),
})
.collect::<Vec<_>>(),
TypeEntryDetails::Struct(TypeEntryStruct { properties, .. }) => properties
.iter_mut()
.map(|prop| &mut prop.type_id)
.collect(),
TypeEntryDetails::Newtype(TypeEntryNewtype { type_id, .. }) => {
vec![type_id]
}
// Unnamed types that can participate in containment cycles.
TypeEntryDetails::Option(type_id) => vec![type_id],
TypeEntryDetails::Array(type_id, _) => vec![type_id],
TypeEntryDetails::Tuple(type_ids) => type_ids.iter_mut().collect(),
_ => Vec::new(),
}
}
#[cfg(test)]
mod tests {
use schema::Schema;
use schemars::JsonSchema;
use crate::test_util::validate_output;
#[test]
fn test_trivial_cycle() {
#[derive(JsonSchema, Schema)]
#[allow(dead_code)]
struct A {
a: Box<A>,
}
validate_output::<A>();
}
#[test]
fn test_optional_trivial_cycle() {
#[derive(JsonSchema, Schema)]
#[allow(dead_code)]
struct A {
a: Option<Box<A>>,
}
validate_output::<A>();
}
#[test]
fn test_enum_trivial_cycles() {
#[derive(JsonSchema, Schema)]
#[allow(dead_code)]
enum A {
Variant0(u64),
Variant1 {
a: u64,
b: Vec<A>,
rop: Option<Box<A>>,
},
Variant2 {
a: Box<A>,
},
Variant3(u64, Box<A>),
Variant4(Option<Box<A>>, String),
}
validate_output::<A>();
}
#[test]
fn test_newtype_trivial_cycle() {
#[derive(JsonSchema, Schema)]
#[allow(dead_code)]
struct A(Box<A>);
validate_output::<A>();
}
#[test]
fn test_abab_cycle() {
#[derive(JsonSchema, Schema)]
#[allow(dead_code)]
struct A(B);
#[derive(JsonSchema, Schema)]
#[allow(dead_code)]
struct B(Box<A>);
validate_output::<A>();
}
}