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[ty] Some more simplifications when rendering constraint sets (#21009)
This PR adds another useful simplification when rendering constraint sets: `T = int` instead of `T = int ∧ T ≠ str`. (The "smaller" constraint `T = int` implies the "larger" constraint `T ≠ str`. Constraint set clauses are intersections, and if one constraint in a clause implies another, we can throw away the "larger" constraint.) While we're here, we also normalize the bounds of a constraint, so that we equate e.g. `T ≤ int | str` with `T ≤ str | int`, and change the ordering of BDD variables so that all constraints with the same typevar are ordered adjacent to each other. Lastly, we also add a new `display_graph` helper method that prints out the full graph structure of a BDD. --------- Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
This commit is contained in:
Douglas Creager
GitHub
parent
81c1d36088
commit
766ed5b5f3
6 changed files with 314 additions and 23 deletions
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@ -22,7 +22,12 @@ use crate::unpack::{Unpack, UnpackPosition};
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/// because a new scope gets inserted before the `Definition` or a new place is inserted
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/// before this `Definition`. However, the ID can be considered stable and it is okay to use
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/// `Definition` in cross-module` salsa queries or as a field on other salsa tracked structs.
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///
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/// # Ordering
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/// Ordering is based on the definition's salsa-assigned id and not on its values.
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/// The id may change between runs, or when the definition was garbage collected and recreated.
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#[salsa::tracked(debug, heap_size=ruff_memory_usage::heap_size)]
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#[derive(Ord, PartialOrd)]
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pub struct Definition<'db> {
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/// The file in which the definition occurs.
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pub file: File,
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@ -8461,7 +8461,9 @@ fn lazy_bound_or_constraints_cycle_initial<'db>(
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}
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/// Where a type variable is bound and usable.
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#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq, salsa::Update, get_size2::GetSize)]
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#[derive(
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Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd, salsa::Update, get_size2::GetSize,
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)]
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pub enum BindingContext<'db> {
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/// The definition of the generic class, function, or type alias that binds this typevar.
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Definition(Definition<'db>),
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@ -8495,7 +8497,9 @@ impl<'db> BindingContext<'db> {
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/// independent of the typevar's bounds or constraints. Two bound typevars have the same identity
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/// if they represent the same logical typevar bound in the same context, even if their bounds
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/// have been materialized differently.
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#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, get_size2::GetSize, salsa::Update)]
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#[derive(
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Debug, Clone, Copy, Eq, Hash, Ord, PartialEq, PartialOrd, get_size2::GetSize, salsa::Update,
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)]
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pub struct BoundTypeVarIdentity<'db> {
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pub(crate) identity: TypeVarIdentity<'db>,
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pub(crate) binding_context: BindingContext<'db>,
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@ -23,6 +23,9 @@
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//! Note that all lower and upper bounds in a constraint must be fully static. We take the bottom
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//! and top materializations of the types to remove any gradual forms if needed.
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//!
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//! Lower and upper bounds must also be normalized. This lets us identify, for instance,
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//! two constraints with equivalent but differently ordered unions as their bounds.
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//!
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//! NOTE: This module is currently in a transitional state. We've added the BDD [`ConstraintSet`]
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//! representation, and updated all of our property checks to build up a constraint set and then
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//! check whether it is ever or always satisfiable, as appropriate. We are not yet inferring
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@ -58,6 +61,7 @@ use std::fmt::Display;
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use itertools::Itertools;
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use rustc_hash::FxHashSet;
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use salsa::plumbing::AsId;
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use crate::Db;
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use crate::types::{BoundTypeVarIdentity, IntersectionType, Type, UnionType};
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@ -183,20 +187,20 @@ impl<'db> ConstraintSet<'db> {
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/// Updates this constraint set to hold the union of itself and another constraint set.
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pub(crate) fn union(&mut self, db: &'db dyn Db, other: Self) -> Self {
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self.node = self.node.or(db, other.node).simplify(db);
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self.node = self.node.or(db, other.node);
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*self
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}
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/// Updates this constraint set to hold the intersection of itself and another constraint set.
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pub(crate) fn intersect(&mut self, db: &'db dyn Db, other: Self) -> Self {
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self.node = self.node.and(db, other.node).simplify(db);
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self.node = self.node.and(db, other.node);
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*self
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}
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/// Returns the negation of this constraint set.
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pub(crate) fn negate(self, db: &'db dyn Db) -> Self {
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Self {
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node: self.node.negate(db).simplify(db),
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node: self.node.negate(db),
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}
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}
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@ -256,7 +260,6 @@ impl From<bool> for ConstraintSet<'_> {
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/// An individual constraint in a constraint set. This restricts a single typevar to be within a
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/// lower and upper bound.
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#[salsa::interned(debug, heap_size=ruff_memory_usage::heap_size)]
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#[derive(PartialOrd, Ord)]
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pub(crate) struct ConstrainedTypeVar<'db> {
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typevar: BoundTypeVarIdentity<'db>,
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lower: Type<'db>,
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@ -292,8 +295,11 @@ impl<'db> ConstrainedTypeVar<'db> {
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return Node::AlwaysTrue;
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}
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let lower = lower.normalized(db);
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let upper = upper.normalized(db);
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Node::new_constraint(db, ConstrainedTypeVar::new(db, typevar, lower, upper))
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}
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fn when_true(self) -> ConstraintAssignment<'db> {
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ConstraintAssignment::Positive(self)
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}
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@ -310,11 +316,37 @@ impl<'db> ConstrainedTypeVar<'db> {
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&& other.upper(db).is_subtype_of(db, self.upper(db))
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}
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/// Defines the ordering of the variables in a constraint set BDD.
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///
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/// If we only care about _correctness_, we can choose any ordering that we want, as long as
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/// it's consistent. However, different orderings can have very different _performance_
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/// characteristics. Many BDD libraries attempt to reorder variables on the fly while building
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/// and working with BDDs. We don't do that, but we have tried to make some simple choices that
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/// have clear wins.
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///
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/// In particular, we compare the _typevars_ of each constraint first, so that all constraints
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/// for a single typevar are guaranteed to be adjacent in the BDD structure. There are several
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/// simplifications that we perform that operate on constraints with the same typevar, and this
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/// ensures that we can find all candidate simplifications more easily.
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fn ordering(self, db: &'db dyn Db) -> impl Ord {
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(self.typevar(db), self.as_id())
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}
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/// Returns whether this constraint implies another — i.e., whether every type that
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/// satisfies this constraint also satisfies `other`.
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///
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/// This is used (among other places) to simplify how we display constraint sets, by removing
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/// redundant constraints from a clause.
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fn implies(self, db: &'db dyn Db, other: Self) -> bool {
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other.contains(db, self)
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}
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/// Returns the intersection of two range constraints, or `None` if the intersection is empty.
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fn intersect(self, db: &'db dyn Db, other: Self) -> Option<Self> {
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// (s₁ ≤ α ≤ t₁) ∧ (s₂ ≤ α ≤ t₂) = (s₁ ∪ s₂) ≤ α ≤ (t₁ ∩ t₂))
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let lower = UnionType::from_elements(db, [self.lower(db), other.lower(db)]);
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let upper = IntersectionType::from_elements(db, [self.upper(db), other.upper(db)]);
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let lower = UnionType::from_elements(db, [self.lower(db), other.lower(db)]).normalized(db);
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let upper =
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IntersectionType::from_elements(db, [self.upper(db), other.upper(db)]).normalized(db);
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// If `lower ≰ upper`, then the intersection is empty, since there is no type that is both
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// greater than `lower`, and less than `upper`.
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@ -390,8 +422,8 @@ impl<'db> ConstrainedTypeVar<'db> {
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/// that point at the same node.
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///
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/// BDD nodes are also _ordered_, meaning that every path from the root of a BDD to a terminal node
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/// visits variables in the same order. [`ConstrainedTypeVar`]s are interned, so we can use the IDs
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/// that salsa assigns to define this order.
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/// visits variables in the same order. [`ConstrainedTypeVar::ordering`] defines the variable
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/// ordering that we use for constraint set BDDs.
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#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, get_size2::GetSize, salsa::Update)]
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enum Node<'db> {
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AlwaysFalse,
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@ -407,13 +439,13 @@ impl<'db> Node<'db> {
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if_true: Node<'db>,
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if_false: Node<'db>,
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) -> Self {
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debug_assert!((if_true.root_constraint(db)).is_none_or(|root_constraint| {
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root_constraint.ordering(db) > constraint.ordering(db)
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}));
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debug_assert!(
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(if_true.root_constraint(db))
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.is_none_or(|root_constraint| root_constraint > constraint)
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);
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debug_assert!(
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(if_false.root_constraint(db))
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.is_none_or(|root_constraint| root_constraint > constraint)
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(if_false.root_constraint(db)).is_none_or(|root_constraint| {
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root_constraint.ordering(db) > constraint.ordering(db)
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})
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);
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if if_true == if_false {
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return if_true;
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@ -762,14 +794,87 @@ impl<'db> Node<'db> {
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Node::AlwaysFalse => f.write_str("never"),
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Node::Interior(_) => {
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let mut clauses = self.node.satisfied_clauses(self.db);
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clauses.simplify();
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clauses.simplify(self.db);
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clauses.display(self.db).fmt(f)
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}
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}
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}
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}
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DisplayNode { node: self, db }
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DisplayNode {
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node: self.simplify(db),
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db,
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}
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}
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/// Displays the full graph structure of this BDD. `prefix` will be output before each line
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/// other than the first. Produces output like the following:
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///
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/// ```text
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/// (T@_ = str)
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/// ┡━₁ (U@_ = str)
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/// │ ┡━₁ always
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/// │ └─₀ (U@_ = bool)
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/// │ ┡━₁ always
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/// │ └─₀ never
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/// └─₀ (T@_ = bool)
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/// ┡━₁ (U@_ = str)
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/// │ ┡━₁ always
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/// │ └─₀ (U@_ = bool)
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/// │ ┡━₁ always
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/// │ └─₀ never
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/// └─₀ never
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/// ```
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#[cfg_attr(not(test), expect(dead_code))] // Keep this around for debugging purposes
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fn display_graph(self, db: &'db dyn Db, prefix: &dyn Display) -> impl Display {
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struct DisplayNode<'a, 'db> {
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db: &'db dyn Db,
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node: Node<'db>,
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prefix: &'a dyn Display,
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}
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impl<'a, 'db> DisplayNode<'a, 'db> {
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fn new(db: &'db dyn Db, node: Node<'db>, prefix: &'a dyn Display) -> Self {
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Self { db, node, prefix }
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}
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}
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impl Display for DisplayNode<'_, '_> {
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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match self.node {
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Node::AlwaysTrue => write!(f, "always"),
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Node::AlwaysFalse => write!(f, "never"),
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Node::Interior(interior) => {
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interior.constraint(self.db).display(self.db).fmt(f)?;
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// Calling display_graph recursively here causes rustc to claim that the
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// expect(unused) up above is unfulfilled!
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write!(
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f,
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"\n{}┡━₁ {}",
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self.prefix,
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DisplayNode::new(
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self.db,
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interior.if_true(self.db),
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&format_args!("{}│ ", self.prefix)
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),
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)?;
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write!(
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f,
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"\n{}└─₀ {}",
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self.prefix,
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DisplayNode::new(
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self.db,
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interior.if_false(self.db),
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&format_args!("{} ", self.prefix)
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),
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)?;
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Ok(())
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}
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}
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}
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}
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DisplayNode::new(db, self, prefix)
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}
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}
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@ -800,7 +905,7 @@ impl<'db> InteriorNode<'db> {
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fn or(self, db: &'db dyn Db, other: Self) -> Node<'db> {
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let self_constraint = self.constraint(db);
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let other_constraint = other.constraint(db);
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match self_constraint.cmp(&other_constraint) {
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match (self_constraint.ordering(db)).cmp(&other_constraint.ordering(db)) {
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Ordering::Equal => Node::new(
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db,
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self_constraint,
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@ -826,7 +931,7 @@ impl<'db> InteriorNode<'db> {
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fn and(self, db: &'db dyn Db, other: Self) -> Node<'db> {
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let self_constraint = self.constraint(db);
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let other_constraint = other.constraint(db);
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match self_constraint.cmp(&other_constraint) {
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match (self_constraint.ordering(db)).cmp(&other_constraint.ordering(db)) {
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Ordering::Equal => Node::new(
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db,
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self_constraint,
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@ -852,7 +957,7 @@ impl<'db> InteriorNode<'db> {
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fn iff(self, db: &'db dyn Db, other: Self) -> Node<'db> {
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let self_constraint = self.constraint(db);
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let other_constraint = other.constraint(db);
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match self_constraint.cmp(&other_constraint) {
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match (self_constraint.ordering(db)).cmp(&other_constraint.ordering(db)) {
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Ordering::Equal => Node::new(
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db,
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self_constraint,
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@ -884,7 +989,7 @@ impl<'db> InteriorNode<'db> {
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// point in the BDD where the assignment can no longer affect the result,
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// and we can return early.
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let self_constraint = self.constraint(db);
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if assignment.constraint() < self_constraint {
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if assignment.constraint().ordering(db) < self_constraint.ordering(db) {
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return (Node::Interior(self), false);
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}
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@ -1141,6 +1246,55 @@ impl<'db> ConstraintAssignment<'db> {
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*self = self.negated();
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}
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/// Returns whether this constraint implies another — i.e., whether every type that
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/// satisfies this constraint also satisfies `other`.
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///
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/// This is used (among other places) to simplify how we display constraint sets, by removing
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/// redundant constraints from a clause.
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fn implies(self, db: &'db dyn Db, other: Self) -> bool {
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match (self, other) {
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// For two positive constraints, one range has to fully contain the other; the smaller
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// constraint implies the larger.
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//
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// ....|----other-----|....
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// ......|---self---|......
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(
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ConstraintAssignment::Positive(self_constraint),
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ConstraintAssignment::Positive(other_constraint),
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) => self_constraint.implies(db, other_constraint),
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// For two negative constraints, one range has to fully contain the other; the ranges
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// represent "holes", though, so the constraint with the larger range implies the one
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// with the smaller.
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//
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// |-----|...other...|-----|
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// |---|.....self......|---|
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(
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ConstraintAssignment::Negative(self_constraint),
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ConstraintAssignment::Negative(other_constraint),
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) => other_constraint.implies(db, self_constraint),
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// For a positive and negative constraint, the ranges have to be disjoint, and the
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// positive range implies the negative range.
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//
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// |---------------|...self...|---|
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// ..|---other---|................|
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(
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ConstraintAssignment::Positive(self_constraint),
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ConstraintAssignment::Negative(other_constraint),
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) => self_constraint.intersect(db, other_constraint).is_none(),
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// It's theoretically possible for a negative constraint to imply a positive constraint
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// if the positive constraint is always satisfied (`Never ≤ T ≤ object`). But we never
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// create constraints of that form, so with our representation, a negative constraint
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// can never imply a positive constraint.
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//
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// |------other-------|
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// |---|...self...|---|
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(ConstraintAssignment::Negative(_), ConstraintAssignment::Positive(_)) => false,
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}
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}
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// Keep this for future debugging needs, even though it's not currently used when rendering
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// constraint sets.
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#[expect(dead_code)]
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@ -1209,6 +1363,43 @@ impl<'db> SatisfiedClause<'db> {
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false
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}
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/// Simplifies this clause by removing constraints that are implied by other constraints in the
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/// clause. (Clauses are the intersection of constraints, so if two clauses are redundant, we
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/// want to remove the larger one and keep the smaller one.)
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///
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/// Returns a boolean that indicates whether any simplifications were made.
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fn simplify(&mut self, db: &'db dyn Db) -> bool {
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let mut changes_made = false;
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let mut i = 0;
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// Loop through each constraint, comparing it with any constraints that appear later in the
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// list.
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'outer: while i < self.constraints.len() {
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let mut j = i + 1;
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while j < self.constraints.len() {
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if self.constraints[j].implies(db, self.constraints[i]) {
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// If constraint `i` is removed, then we don't need to compare it with any
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// later constraints in the list. Note that we continue the outer loop, instead
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// of breaking from the inner loop, so that we don't bump index `i` below.
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// (We'll have swapped another element into place at that index, and want to
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// make sure that we process it.)
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self.constraints.swap_remove(i);
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changes_made = true;
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continue 'outer;
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} else if self.constraints[i].implies(db, self.constraints[j]) {
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// If constraint `j` is removed, then we can continue the inner loop. We will
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// swap a new element into place at index `j`, and will continue comparing the
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// constraint at index `i` with later constraints.
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self.constraints.swap_remove(j);
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changes_made = true;
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} else {
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j += 1;
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}
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}
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i += 1;
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}
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changes_made
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}
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fn display(&self, db: &'db dyn Db) -> String {
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// This is a bit heavy-handed, but we need to output the constraints in a consistent order
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// even though Salsa IDs are assigned non-deterministically. This Display output is only
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|
|
@ -1258,7 +1449,13 @@ impl<'db> SatisfiedClauses<'db> {
|
|||
/// Simplifies the DNF representation, removing redundancies that do not change the underlying
|
||||
/// function. (This is used when displaying a BDD, to make sure that the representation that we
|
||||
/// show is as simple as possible while still producing the same results.)
|
||||
fn simplify(&mut self) {
|
||||
fn simplify(&mut self, db: &'db dyn Db) {
|
||||
// First simplify each clause individually, by removing constraints that are implied by
|
||||
// other constraints in the clause.
|
||||
for clause in &mut self.clauses {
|
||||
clause.simplify(db);
|
||||
}
|
||||
|
||||
while self.simplify_one_round() {
|
||||
// Keep going
|
||||
}
|
||||
|
|
@ -1340,3 +1537,47 @@ impl<'db> SatisfiedClauses<'db> {
|
|||
clauses.join(" ∨ ")
|
||||
}
|
||||
}
|
||||
|
||||
#[cfg(test)]
|
||||
mod tests {
|
||||
use super::*;
|
||||
|
||||
use indoc::indoc;
|
||||
use pretty_assertions::assert_eq;
|
||||
|
||||
use crate::db::tests::setup_db;
|
||||
use crate::types::{BoundTypeVarInstance, KnownClass, TypeVarVariance};
|
||||
|
||||
#[test]
|
||||
fn test_display_graph_output() {
|
||||
let expected = indoc! {r#"
|
||||
(T = str)
|
||||
┡━₁ (U = str)
|
||||
│ ┡━₁ always
|
||||
│ └─₀ (U = bool)
|
||||
│ ┡━₁ always
|
||||
│ └─₀ never
|
||||
└─₀ (T = bool)
|
||||
┡━₁ (U = str)
|
||||
│ ┡━₁ always
|
||||
│ └─₀ (U = bool)
|
||||
│ ┡━₁ always
|
||||
│ └─₀ never
|
||||
└─₀ never
|
||||
"#}
|
||||
.trim_end();
|
||||
|
||||
let db = setup_db();
|
||||
let t = BoundTypeVarInstance::synthetic(&db, "T", TypeVarVariance::Invariant);
|
||||
let u = BoundTypeVarInstance::synthetic(&db, "U", TypeVarVariance::Invariant);
|
||||
let bool_type = KnownClass::Bool.to_instance(&db);
|
||||
let str_type = KnownClass::Str.to_instance(&db);
|
||||
let t_str = ConstraintSet::range(&db, str_type, t.identity(&db), str_type);
|
||||
let t_bool = ConstraintSet::range(&db, bool_type, t.identity(&db), bool_type);
|
||||
let u_str = ConstraintSet::range(&db, str_type, u.identity(&db), str_type);
|
||||
let u_bool = ConstraintSet::range(&db, bool_type, u.identity(&db), bool_type);
|
||||
let constraints = (t_str.or(&db, || t_bool)).and(&db, || u_str.or(&db, || u_bool));
|
||||
let actual = constraints.node.display_graph(&db, &"").to_string();
|
||||
assert_eq!(actual, expected);
|
||||
}
|
||||
}
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue