1 files changed, 72 insertions, 0 deletions
diff --git a/vendor/chalk-engine/src/context.rs b/vendor/chalk-engine/src/context.rs
new file mode 100644
index 000000000..fa418dfd4
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+++ b/vendor/chalk-engine/src/context.rs
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+//! Defines traits used to embed the chalk-engine in another crate.
+//!
+//! chalk and rustc both define types which implement the traits in this
+//! module. This allows each user of chalk-engine to define their own
+//! `DomainGoal` type, add arena lifetime parameters, and more. See
+//! [`Context`] trait for a list of types.
+
+use crate::CompleteAnswer;
+use chalk_ir::interner::Interner;
+use chalk_ir::Substitution;
+use std::fmt::Debug;
+
+pub enum AnswerResult<I: Interner> {
+    /// The next available answer.
+    Answer(CompleteAnswer<I>),
+
+    /// No answer could be returned because there are no more solutions.
+    NoMoreSolutions,
+
+    /// No answer could be returned because the goal has floundered.
+    Floundered,
+
+    // No answer could be returned *yet*, because we exceeded our
+    // quantum (`should_continue` returned false).
+    QuantumExceeded,
+}
+
+impl<I: Interner> AnswerResult<I> {
+    pub fn is_answer(&self) -> bool {
+        matches!(self, Self::Answer(_))
+    }
+
+    pub fn answer(self) -> CompleteAnswer<I> {
+        match self {
+            Self::Answer(answer) => answer,
+            _ => panic!("Not an answer."),
+        }
+    }
+
+    pub fn is_no_more_solutions(&self) -> bool {
+        matches!(self, Self::NoMoreSolutions)
+    }
+
+    pub fn is_quantum_exceeded(&self) -> bool {
+        matches!(self, Self::QuantumExceeded)
+    }
+}
+
+impl<I: Interner> Debug for AnswerResult<I> {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            AnswerResult::Answer(answer) => write!(fmt, "{:?}", answer),
+            AnswerResult::Floundered => write!(fmt, "Floundered"),
+            AnswerResult::NoMoreSolutions => write!(fmt, "None"),
+            AnswerResult::QuantumExceeded => write!(fmt, "QuantumExceeded"),
+        }
+    }
+}
+
+pub trait AnswerStream<I: Interner> {
+    /// Gets the next answer for a given goal, but doesn't increment the answer index.
+    /// Calling this or `next_answer` again will give the same answer.
+    fn peek_answer(&mut self, should_continue: impl Fn() -> bool) -> AnswerResult<I>;
+
+    /// Gets the next answer for a given goal, incrementing the answer index.
+    /// Calling this or `peek_answer` again will give the next answer.
+    fn next_answer(&mut self, should_continue: impl Fn() -> bool) -> AnswerResult<I>;
+
+    /// Invokes `test` with each possible future answer, returning true immediately
+    /// if we find any answer for which `test` returns true.
+    fn any_future_answer(&self, test: impl Fn(&Substitution<I>) -> bool) -> bool;
+}