[red-knot] Add a convenience method for constructing a union from a list of elements (#13315)

crates/red_knot_python_semantic/src/types.rs

@@ -144,14 +144,7 @@ pub(crate) fn definitions_ty<'db>(
         .expect("definitions_ty should never be called with zero definitions and no unbound_ty.");
 
     if let Some(second) = all_types.next() {
-        let mut builder = UnionBuilder::new(db);
+        UnionType::from_elements(db, [first, second].into_iter().chain(all_types))
-        builder = builder.add(first).add(second);
-
-        for variant in all_types {
-            builder = builder.add(variant);
-        }
-
-        builder.build()
     } else {
         first
     }
@@ -410,13 +403,7 @@ impl<'db> Type<'db> {
     fn iterate(&self, db: &'db dyn Db) -> IterationOutcome<'db> {
         if let Type::Tuple(tuple_type) = self {
             return IterationOutcome::Iterable {
-                element_ty: tuple_type
+                element_ty: UnionType::from_elements(db, &**tuple_type.elements(db)),
-                    .elements(db)
-                    .iter()
-                    .fold(UnionBuilder::new(db), |builder, element| {
-                        builder.add(*element)
-                    })
-                    .build(),
             };
         }
 
@@ -497,6 +484,12 @@ impl<'db> Type<'db> {
     }
 }
 
+impl<'db> From<&Type<'db>> for Type<'db> {
+    fn from(value: &Type<'db>) -> Self {
+        *value
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 enum IterationOutcome<'db> {
     Iterable { element_ty: Type<'db> },
@@ -636,19 +629,28 @@ impl<'db> UnionType<'db> {
         self.elements(db).contains(&ty)
     }
 
+    /// Create a union from a list of elements
+    /// (which may be eagerly simplified into a different variant of [`Type`] altogether)
+    pub fn from_elements<T: Into<Type<'db>>>(
+        db: &'db dyn Db,
+        elements: impl IntoIterator<Item = T>,
+    ) -> Type<'db> {
+        elements
+            .into_iter()
+            .fold(UnionBuilder::new(db), |builder, element| {
+                builder.add(element.into())
+            })
+            .build()
+    }
+
     /// Apply a transformation function to all elements of the union,
     /// and create a new union from the resulting set of types
     pub fn map(
         &self,
         db: &'db dyn Db,
-        mut transform_fn: impl FnMut(&Type<'db>) -> Type<'db>,
+        transform_fn: impl Fn(&Type<'db>) -> Type<'db>,
     ) -> Type<'db> {
-        self.elements(db)
+        Self::from_elements(db, self.elements(db).into_iter().map(transform_fn))
-            .into_iter()
-            .fold(UnionBuilder::new(db), |builder, element| {
-                builder.add(transform_fn(element))
-            })
-            .build()
     }
 }
 

crates/red_knot_python_semantic/src/types/builder.rs

@@ -169,11 +169,12 @@ impl<'db> IntersectionBuilder<'db> {
         if self.intersections.len() == 1 {
             self.intersections.pop().unwrap().build(self.db)
         } else {
-            let mut builder = UnionBuilder::new(self.db);
+            UnionType::from_elements(
-            for inner in self.intersections {
+                self.db,
-                builder = builder.add(inner.build(self.db));
+                self.intersections
-            }
+                    .into_iter()
-            builder.build()
+                    .map(|inner| inner.build(self.db)),
+            )
         }
     }
 }
@@ -271,11 +272,11 @@ impl<'db> InnerIntersectionBuilder<'db> {
 
 #[cfg(test)]
 mod tests {
-    use super::{IntersectionBuilder, IntersectionType, Type, UnionBuilder, UnionType};
+    use super::{IntersectionBuilder, IntersectionType, Type, UnionType};
     use crate::db::tests::TestDb;
     use crate::program::{Program, SearchPathSettings};
     use crate::python_version::PythonVersion;
-    use crate::types::builtins_symbol_ty;
+    use crate::types::{builtins_symbol_ty, UnionBuilder};
     use crate::ProgramSettings;
     use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
 
@@ -310,11 +311,7 @@ mod tests {
         let db = setup_db();
         let t0 = Type::IntLiteral(0);
         let t1 = Type::IntLiteral(1);
-        let union = UnionBuilder::new(&db)
+        let union = UnionType::from_elements(&db, [t0, t1]).expect_union();
-            .add(t0)
-            .add(t1)
-            .build()
-            .expect_union();
 
         assert_eq!(union.elements_vec(&db), &[t0, t1]);
     }
@@ -323,8 +320,7 @@ mod tests {
     fn build_union_single() {
         let db = setup_db();
         let t0 = Type::IntLiteral(0);
-        let ty = UnionBuilder::new(&db).add(t0).build();
+        let ty = UnionType::from_elements(&db, [t0]);
-
         assert_eq!(ty, t0);
     }
 
@@ -332,7 +328,6 @@ mod tests {
     fn build_union_empty() {
         let db = setup_db();
         let ty = UnionBuilder::new(&db).build();
-
         assert_eq!(ty, Type::Never);
     }
 
@@ -340,8 +335,7 @@ mod tests {
     fn build_union_never() {
         let db = setup_db();
         let t0 = Type::IntLiteral(0);
-        let ty = UnionBuilder::new(&db).add(t0).add(Type::Never).build();
+        let ty = UnionType::from_elements(&db, [t0, Type::Never]);
-
         assert_eq!(ty, t0);
     }
 
@@ -355,21 +349,10 @@ mod tests {
         let t2 = Type::BooleanLiteral(false);
         let t3 = Type::IntLiteral(17);
 
-        let union = UnionBuilder::new(&db)
+        let union = UnionType::from_elements(&db, [t0, t1, t3]).expect_union();
-            .add(t0)
-            .add(t1)
-            .add(t3)
-            .build()
-            .expect_union();
         assert_eq!(union.elements_vec(&db), &[t0, t3]);
-        let union = UnionBuilder::new(&db)
-            .add(t0)
-            .add(t1)
-            .add(t2)
-            .add(t3)
-            .build()
-            .expect_union();
 
+        let union = UnionType::from_elements(&db, [t0, t1, t2, t3]).expect_union();
         assert_eq!(union.elements_vec(&db), &[bool_ty, t3]);
     }
 
@@ -379,12 +362,8 @@ mod tests {
         let t0 = Type::IntLiteral(0);
         let t1 = Type::IntLiteral(1);
         let t2 = Type::IntLiteral(2);
-        let u1 = UnionBuilder::new(&db).add(t0).add(t1).build();
+        let u1 = UnionType::from_elements(&db, [t0, t1]);
-        let union = UnionBuilder::new(&db)
+        let union = UnionType::from_elements(&db, [u1, t2]).expect_union();
-            .add(u1)
-            .add(t2)
-            .build()
-            .expect_union();
 
         assert_eq!(union.elements_vec(&db), &[t0, t1, t2]);
     }
@@ -460,7 +439,7 @@ mod tests {
         let t0 = Type::IntLiteral(0);
         let t1 = Type::IntLiteral(1);
         let ta = Type::Any;
-        let u0 = UnionBuilder::new(&db).add(t0).add(t1).build();
+        let u0 = UnionType::from_elements(&db, [t0, t1]);
 
         let union = IntersectionBuilder::new(&db)
             .add_positive(ta)

crates/red_knot_python_semantic/src/types/display.rs

@@ -253,7 +253,7 @@ mod tests {
     use ruff_db::system::{DbWithTestSystem, SystemPathBuf};
 
     use crate::db::tests::TestDb;
-    use crate::types::{global_symbol_ty, BytesLiteralType, StringLiteralType, Type, UnionBuilder};
+    use crate::types::{global_symbol_ty, BytesLiteralType, StringLiteralType, Type, UnionType};
     use crate::{Program, ProgramSettings, PythonVersion, SearchPathSettings};
 
     fn setup_db() -> TestDb {
@@ -295,7 +295,7 @@ mod tests {
         )?;
         let mod_file = system_path_to_file(&db, "src/main.py").expect("Expected file to exist.");
 
-        let vec: Vec<Type<'_>> = vec![
+        let union_elements = &[
             Type::Unknown,
             Type::IntLiteral(-1),
             global_symbol_ty(&db, mod_file, "A"),
@@ -311,10 +311,7 @@ mod tests {
             Type::BooleanLiteral(true),
             Type::None,
         ];
-        let builder = vec.iter().fold(UnionBuilder::new(&db), |builder, literal| {
+        let union = UnionType::from_elements(&db, union_elements).expect_union();
-            builder.add(*literal)
-        });
-        let union = builder.build().expect_union();
         let display = format!("{}", union.display(&db));
         assert_eq!(
             display,

crates/red_knot_python_semantic/src/types/infer.rs

@@ -49,7 +49,7 @@ use crate::stdlib::builtins_module_scope;
 use crate::types::diagnostic::{TypeCheckDiagnostic, TypeCheckDiagnostics};
 use crate::types::{
     builtins_symbol_ty, definitions_ty, global_symbol_ty, symbol_ty, BytesLiteralType, ClassType,
-    FunctionType, StringLiteralType, TupleType, Type, UnionBuilder,
+    FunctionType, StringLiteralType, TupleType, Type, UnionType,
 };
 use crate::Db;
 
@@ -1827,10 +1827,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         let body_ty = self.infer_expression(body);
         let orelse_ty = self.infer_expression(orelse);
 
-        UnionBuilder::new(self.db)
+        UnionType::from_elements(self.db, [body_ty, orelse_ty])
-            .add(body_ty)
-            .add(orelse_ty)
-            .build()
     }
 
     fn infer_lambda_body(&mut self, lambda_expression: &ast::ExprLambda) {