[red-knot] add more types (#11135)

Fill out the representation of types to a few more cases (especially
unions and intersections) before going too far with type evaluation.

crates/red_knot/src/types.rs

@@ -1,6 +1,7 @@
 #![allow(dead_code)]
 use crate::Name;
 use ruff_index::{newtype_index, IndexVec};
+use rustc_hash::FxHashSet;
 
 #[newtype_index]
 pub(crate) struct TypeId;
@@ -12,16 +13,18 @@ impl TypeId {
 }
 
 /// Arena holding all known types
-#[derive(Default)]
+#[derive(Debug, Default)]
 pub(crate) struct TypeEnvironment {
     types_by_id: IndexVec<TypeId, Type>,
 }
 
 impl TypeEnvironment {
     pub(crate) fn add_class(&mut self, name: &str) -> TypeId {
-        let class = Type::Class(ClassType {
-            name: Name::new(name),
-        });
+        let class = Type::Instance {
+            instance_of: ClassType {
+                name: Name::new(name),
+            },
+        };
         self.types_by_id.push(class)
     }
 
@@ -37,40 +40,148 @@ impl TypeEnvironment {
     }
 }
 
+#[derive(Debug)]
 pub(crate) enum Type {
-    Class(ClassType),
+    /// a specific function
     Function(FunctionType),
+    /// the set of Python objects with this class in their __class__'s method resolution order
+    Instance {
+        instance_of: ClassType,
+    },
+    Union(UnionType),
+    Intersection(IntersectionType),
+    /// the dynamic or gradual type: a statically-unknown set of values
+    Any,
+    /// the empty set of values
+    Never,
+    /// unknown type (no annotation)
+    /// equivalent to Any, or to object in strict mode
+    Unknown,
+    /// name is not bound to any value
+    Unbound,
+    // TODO protocols, callable types, overloads, generics, type vars
 }
 
 impl Type {
-    pub(crate) fn name(&self) -> &str {
+    pub(crate) fn name(&self) -> Option<&str> {
         match self {
-            Type::Class(inner) => inner.name(),
-            Type::Function(inner) => inner.name(),
+            Type::Instance { instance_of: class } => Some(class.name()),
+            Type::Function(func) => Some(func.name()),
+            Type::Union(_) => None,
+            Type::Intersection(_) => None,
+            Type::Any => Some("Any"),
+            Type::Never => Some("Never"),
+            Type::Unknown => Some("Unknown"),
+            Type::Unbound => Some("Unbound"),
         }
     }
+
+    fn display<'a>(&'a self, env: &'a TypeEnvironment) -> DisplayType<'a> {
+        DisplayType { ty: self, env }
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+struct DisplayType<'a> {
+    ty: &'a Type,
+    env: &'a TypeEnvironment,
 }
 
+impl std::fmt::Display for DisplayType<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self.ty {
+            Type::Union(inner) => inner.display(f, self.env),
+            Type::Intersection(inner) => inner.display(f, self.env),
+            _ => {
+                let name = self.ty.name().expect("type should have a name");
+                f.write_str(name)
+            }
+        }
+    }
+}
+
+#[derive(Debug)]
 pub(crate) struct ClassType {
     name: Name,
 }
 
 impl ClassType {
-    pub(crate) fn name(&self) -> &str {
+    fn name(&self) -> &str {
         self.name.as_str()
     }
 }
 
+#[derive(Debug)]
 pub(crate) struct FunctionType {
     name: Name,
 }
 
 impl FunctionType {
-    pub(crate) fn name(&self) -> &str {
+    fn name(&self) -> &str {
         self.name.as_str()
     }
 }
 
+#[derive(Debug)]
+pub(crate) struct UnionType {
+    // the union type includes values in any of these types
+    elements: FxHashSet<TypeId>,
+}
+
+impl UnionType {
+    fn display(&self, f: &mut std::fmt::Formatter<'_>, env: &TypeEnvironment) -> std::fmt::Result {
+        f.write_str("(")?;
+        let mut first = true;
+        for elem_id in self.elements.iter() {
+            let ty = env.type_for_id(*elem_id);
+            if !first {
+                f.write_str(" | ")?;
+            };
+            first = false;
+            write!(f, "{}", ty.display(env))?;
+        }
+        f.write_str(")")
+    }
+}
+
+// Negation types aren't expressible in annotations, and are most likely to arise from type
+// narrowing along with intersections (e.g. `if not isinstance(...)`), so we represent them
+// directly in intersections rather than as a separate type. This sacrifices some efficiency in the
+// case where a Not appears outside an intersection (unclear when that could even happen, but we'd
+// have to represent it as a single-element intersection if it did) in exchange for better
+// efficiency in the not-within-intersection case.
+#[derive(Debug)]
+pub(crate) struct IntersectionType {
+    // the intersection type includes only values in all of these types
+    positive: FxHashSet<TypeId>,
+    // negated elements of the intersection, e.g.
+    negative: FxHashSet<TypeId>,
+}
+
+impl IntersectionType {
+    fn display(&self, f: &mut std::fmt::Formatter<'_>, env: &TypeEnvironment) -> std::fmt::Result {
+        f.write_str("(")?;
+        let mut first = true;
+        for (neg, elem_id) in self
+            .positive
+            .iter()
+            .map(|elem_id| (false, elem_id))
+            .chain(self.negative.iter().map(|elem_id| (true, elem_id)))
+        {
+            let ty = env.type_for_id(*elem_id);
+            if !first {
+                f.write_str(" & ")?;
+            };
+            first = false;
+            if neg {
+                f.write_str("~")?;
+            };
+            write!(f, "{}", ty.display(env))?;
+        }
+        f.write_str(")")
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::types::TypeEnvironment;
@@ -79,13 +190,13 @@ mod tests {
     fn add_class() {
         let mut env = TypeEnvironment::default();
         let cid = env.add_class("C");
-        assert_eq!(cid.ty(&env).name(), "C");
+        assert_eq!(cid.ty(&env).name(), Some("C"));
     }
 
     #[test]
     fn add_function() {
         let mut env = TypeEnvironment::default();
         let fid = env.add_function("func");
-        assert_eq!(fid.ty(&env).name(), "func");
+        assert_eq!(fid.ty(&env).name(), Some("func"));
     }
 }