1 files changed, 134 insertions, 0 deletions
diff --git a/vendor/chalk-solve-0.87.0/src/solve/truncate.rs b/vendor/chalk-solve-0.87.0/src/solve/truncate.rs
new file mode 100644
index 000000000..1ed47b94f
--- /dev/null
+++ b/vendor/chalk-solve-0.87.0/src/solve/truncate.rs
@@ -0,0 +1,134 @@
+//!
+
+use crate::infer::InferenceTable;
+use chalk_ir::interner::Interner;
+use chalk_ir::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor};
+use chalk_ir::*;
+use std::cmp::max;
+use std::ops::ControlFlow;
+
+/// "Truncation" (called "abstraction" in the papers referenced below)
+/// refers to the act of modifying a goal or answer that has become
+/// too large in order to guarantee termination.
+///
+/// Currently we don't perform truncation (but it might me readded later).
+///
+/// Citations:
+///
+/// - Terminating Evaluation of Logic Programs with Finite Three-Valued Models
+///   - Riguzzi and Swift; ACM Transactions on Computational Logic 2013
+/// - Radial Restraint
+///   - Grosof and Swift; 2013
+pub fn needs_truncation<I: Interner>(
+    interner: I,
+    infer: &mut InferenceTable<I>,
+    max_size: usize,
+    value: impl TypeVisitable<I>,
+) -> bool {
+    let mut visitor = TySizeVisitor::new(interner, infer);
+    value.visit_with(&mut visitor, DebruijnIndex::INNERMOST);
+
+    visitor.max_size > max_size
+}
+
+struct TySizeVisitor<'infer, I: Interner> {
+    interner: I,
+    infer: &'infer mut InferenceTable<I>,
+    size: usize,
+    depth: usize,
+    max_size: usize,
+}
+
+impl<'infer, I: Interner> TySizeVisitor<'infer, I> {
+    fn new(interner: I, infer: &'infer mut InferenceTable<I>) -> Self {
+        Self {
+            interner,
+            infer,
+            size: 0,
+            depth: 0,
+            max_size: 0,
+        }
+    }
+}
+
+impl<'infer, I: Interner> TypeVisitor<I> for TySizeVisitor<'infer, I> {
+    type BreakTy = ();
+
+    fn as_dyn(&mut self) -> &mut dyn TypeVisitor<I, BreakTy = Self::BreakTy> {
+        self
+    }
+
+    fn visit_ty(&mut self, ty: &Ty<I>, outer_binder: DebruijnIndex) -> ControlFlow<()> {
+        if let Some(normalized_ty) = self.infer.normalize_ty_shallow(self.interner, ty) {
+            normalized_ty.visit_with(self, outer_binder);
+            return ControlFlow::Continue(());
+        }
+
+        self.size += 1;
+        self.max_size = max(self.size, self.max_size);
+
+        self.depth += 1;
+        ty.super_visit_with(self, outer_binder);
+        self.depth -= 1;
+
+        // When we get back to the first invocation, clear the counters.
+        // We process each outermost type independently.
+        if self.depth == 0 {
+            self.size = 0;
+        }
+        ControlFlow::Continue(())
+    }
+
+    fn interner(&self) -> I {
+        self.interner
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use chalk_integration::{arg, ty};
+
+    #[test]
+    fn one_type() {
+        use chalk_integration::interner::ChalkIr;
+        let interner = ChalkIr;
+        let mut table = InferenceTable::<chalk_integration::interner::ChalkIr>::new();
+        let _u1 = table.new_universe();
+
+        // Vec<Vec<Vec<Vec<T>>>>
+        let ty0 = ty!(apply (item 0)
+                      (apply (item 0)
+                       (apply (item 0)
+                        (apply (item 0)
+                         (placeholder 1)))));
+
+        let mut visitor = TySizeVisitor::new(interner, &mut table);
+        ty0.visit_with(&mut visitor, DebruijnIndex::INNERMOST);
+        assert!(visitor.max_size == 5);
+    }
+
+    #[test]
+    fn multiple_types() {
+        use chalk_integration::interner::ChalkIr;
+        let interner = ChalkIr;
+        let mut table = InferenceTable::<chalk_integration::interner::ChalkIr>::new();
+        let _u1 = table.new_universe();
+
+        // Vec<Vec<Vec<Vec<T>>>>
+        let ty0 = ty!(apply (item 0)
+                      (apply (item 0)
+                       (apply (item 0)
+                        (apply (item 0)
+                         (placeholder 1)))));
+
+        let ty1 = ty!(apply (item 0)
+                      (apply (item 0)
+                       (apply (item 0)
+                        (placeholder 1))));
+
+        let mut visitor = TySizeVisitor::new(interner, &mut table);
+        vec![&ty0, &ty1].visit_with(&mut visitor, DebruijnIndex::INNERMOST);
+        assert!(visitor.max_size == 5);
+    }
+}