[red-knot] Factor out shared unpacking logic (#16595)

## Summary

This PR refactors the common logic for unpacking in assignment, for loops, and with items.

## Test Plan

Make sure existing tests pass.

---------

Co-authored-by: Dhruv Manilawala <dhruvmanila@gmail.com>
This commit is contained in:
Eric Mark Martin 2025-03-28 14:22:51 -04:00 committed by GitHub
parent 0e48940ea4
commit 78b0b5a3ab
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
5 changed files with 211 additions and 257 deletions

View file

@ -38,7 +38,7 @@ use crate::semantic_index::visibility_constraints::{
ScopedVisibilityConstraintId, VisibilityConstraintsBuilder,
};
use crate::semantic_index::SemanticIndex;
use crate::unpack::{Unpack, UnpackValue};
use crate::unpack::{Unpack, UnpackKind, UnpackPosition, UnpackValue};
use crate::Db;
mod except_handlers;
@ -831,6 +831,64 @@ impl<'db> SemanticIndexBuilder<'db> {
debug_assert_eq!(existing_definition, None);
}
/// Add an unpackable assignment for the given [`Unpackable`].
///
/// This method handles assignments that can contain unpacking like assignment statements,
/// for statements, etc.
fn add_unpackable_assignment(
&mut self,
unpackable: &Unpackable<'db>,
target: &'db ast::Expr,
value: Expression<'db>,
) {
// We only handle assignments to names and unpackings here, other targets like
// attribute and subscript are handled separately as they don't create a new
// definition.
let current_assignment = match target {
ast::Expr::List(_) | ast::Expr::Tuple(_) => {
let unpack = Some(Unpack::new(
self.db,
self.file,
self.current_scope(),
// SAFETY: `target` belongs to the `self.module` tree
#[allow(unsafe_code)]
unsafe {
AstNodeRef::new(self.module.clone(), target)
},
UnpackValue::new(unpackable.kind(), value),
countme::Count::default(),
));
Some(unpackable.as_current_assignment(unpack))
}
ast::Expr::Name(_) => Some(unpackable.as_current_assignment(None)),
ast::Expr::Attribute(ast::ExprAttribute {
value: object,
attr,
..
}) => {
self.register_attribute_assignment(
object,
attr,
unpackable.as_attribute_assignment(value),
);
None
}
_ => None,
};
if let Some(current_assignment) = current_assignment {
self.push_assignment(current_assignment);
}
self.visit_expr(target);
if current_assignment.is_some() {
// Only need to pop in the case where we pushed something
self.pop_assignment();
}
}
pub(super) fn build(mut self) -> SemanticIndex<'db> {
let module = self.module;
self.visit_body(module.suite());
@ -1130,59 +1188,7 @@ where
let value = self.add_standalone_expression(&node.value);
for target in &node.targets {
// We only handle assignments to names and unpackings here, other targets like
// attribute and subscript are handled separately as they don't create a new
// definition.
let current_assignment = match target {
ast::Expr::List(_) | ast::Expr::Tuple(_) => {
Some(CurrentAssignment::Assign {
node,
first: true,
unpack: Some(Unpack::new(
self.db,
self.file,
self.current_scope(),
// SAFETY: `target` belongs to the `self.module` tree
#[allow(unsafe_code)]
unsafe {
AstNodeRef::new(self.module.clone(), target)
},
UnpackValue::Assign(value),
countme::Count::default(),
)),
})
}
ast::Expr::Name(_) => Some(CurrentAssignment::Assign {
node,
unpack: None,
first: false,
}),
ast::Expr::Attribute(ast::ExprAttribute {
value: object,
attr,
..
}) => {
self.register_attribute_assignment(
object,
attr,
AttributeAssignment::Unannotated { value },
);
None
}
_ => None,
};
if let Some(current_assignment) = current_assignment {
self.push_assignment(current_assignment);
}
self.visit_expr(target);
if current_assignment.is_some() {
// Only need to pop in the case where we pushed something
self.pop_assignment();
}
self.add_unpackable_assignment(&Unpackable::Assign(node), target, value);
}
}
ast::Stmt::AnnAssign(node) => {
@ -1373,7 +1379,7 @@ where
is_async,
..
}) => {
for item @ ruff_python_ast::WithItem {
for item @ ast::WithItem {
range: _,
context_expr,
optional_vars,
@ -1382,55 +1388,14 @@ where
self.visit_expr(context_expr);
if let Some(optional_vars) = optional_vars.as_deref() {
let context_manager = self.add_standalone_expression(context_expr);
let current_assignment = match optional_vars {
ast::Expr::Tuple(_) | ast::Expr::List(_) => {
Some(CurrentAssignment::WithItem {
self.add_unpackable_assignment(
&Unpackable::WithItem {
item,
first: true,
is_async: *is_async,
unpack: Some(Unpack::new(
self.db,
self.file,
self.current_scope(),
// SAFETY: the node `optional_vars` belongs to the `self.module` tree
#[allow(unsafe_code)]
unsafe {
AstNodeRef::new(self.module.clone(), optional_vars)
},
UnpackValue::ContextManager(context_manager),
countme::Count::default(),
)),
})
}
ast::Expr::Name(_) => Some(CurrentAssignment::WithItem {
item,
is_async: *is_async,
unpack: None,
// `false` is arbitrary here---we don't actually use it other than in the actual unpacks
first: false,
}),
ast::Expr::Attribute(ast::ExprAttribute {
value: object,
attr,
..
}) => {
self.register_attribute_assignment(
object,
attr,
AttributeAssignment::ContextManager { context_manager },
optional_vars,
context_manager,
);
None
}
_ => None,
};
if let Some(current_assignment) = current_assignment {
self.push_assignment(current_assignment);
}
self.visit_expr(optional_vars);
if current_assignment.is_some() {
self.pop_assignment();
}
}
}
self.visit_body(body);
@ -1455,52 +1420,7 @@ where
let pre_loop = self.flow_snapshot();
let current_assignment = match &**target {
ast::Expr::List(_) | ast::Expr::Tuple(_) => Some(CurrentAssignment::For {
node: for_stmt,
first: true,
unpack: Some(Unpack::new(
self.db,
self.file,
self.current_scope(),
// SAFETY: the node `target` belongs to the `self.module` tree
#[allow(unsafe_code)]
unsafe {
AstNodeRef::new(self.module.clone(), target)
},
UnpackValue::Iterable(iter_expr),
countme::Count::default(),
)),
}),
ast::Expr::Name(_) => Some(CurrentAssignment::For {
node: for_stmt,
unpack: None,
first: false,
}),
ast::Expr::Attribute(ast::ExprAttribute {
value: object,
attr,
..
}) => {
self.register_attribute_assignment(
object,
attr,
AttributeAssignment::Iterable {
iterable: iter_expr,
},
);
None
}
_ => None,
};
if let Some(current_assignment) = current_assignment {
self.push_assignment(current_assignment);
}
self.visit_expr(target);
if current_assignment.is_some() {
self.pop_assignment();
}
self.add_unpackable_assignment(&Unpackable::For(for_stmt), target, iter_expr);
let outer_loop = self.push_loop();
self.visit_body(body);
@ -1737,18 +1657,13 @@ where
if is_definition {
match self.current_assignment() {
Some(CurrentAssignment::Assign {
node,
first,
unpack,
}) => {
Some(CurrentAssignment::Assign { node, unpack }) => {
self.add_definition(
symbol,
AssignmentDefinitionNodeRef {
unpack,
value: &node.value,
name: name_node,
first,
},
);
}
@ -1758,16 +1673,11 @@ where
Some(CurrentAssignment::AugAssign(aug_assign)) => {
self.add_definition(symbol, aug_assign);
}
Some(CurrentAssignment::For {
node,
first,
unpack,
}) => {
Some(CurrentAssignment::For { node, unpack }) => {
self.add_definition(
symbol,
ForStmtDefinitionNodeRef {
unpack,
first,
iterable: &node.iter,
name: name_node,
is_async: node.is_async,
@ -1793,7 +1703,6 @@ where
}
Some(CurrentAssignment::WithItem {
item,
first,
is_async,
unpack,
}) => {
@ -1803,7 +1712,6 @@ where
unpack,
context_expr: &item.context_expr,
name: name_node,
first,
is_async,
},
);
@ -1812,13 +1720,11 @@ where
}
}
if let Some(
CurrentAssignment::Assign { first, .. }
| CurrentAssignment::For { first, .. }
| CurrentAssignment::WithItem { first, .. },
) = self.current_assignment_mut()
if let Some(unpack_position) = self
.current_assignment_mut()
.and_then(CurrentAssignment::unpack_position_mut)
{
*first = false;
*unpack_position = UnpackPosition::Other;
}
walk_expr(self, expr);
@ -1987,20 +1893,10 @@ where
ctx: ExprContext::Store,
range: _,
}) => {
if let Some(
CurrentAssignment::Assign {
unpack: Some(unpack),
..
}
| CurrentAssignment::For {
unpack: Some(unpack),
..
}
| CurrentAssignment::WithItem {
unpack: Some(unpack),
..
},
) = self.current_assignment()
if let Some(unpack) = self
.current_assignment()
.as_ref()
.and_then(CurrentAssignment::unpack)
{
self.register_attribute_assignment(
object,
@ -2075,15 +1971,13 @@ where
enum CurrentAssignment<'a> {
Assign {
node: &'a ast::StmtAssign,
first: bool,
unpack: Option<Unpack<'a>>,
unpack: Option<(UnpackPosition, Unpack<'a>)>,
},
AnnAssign(&'a ast::StmtAnnAssign),
AugAssign(&'a ast::StmtAugAssign),
For {
node: &'a ast::StmtFor,
first: bool,
unpack: Option<Unpack<'a>>,
unpack: Option<(UnpackPosition, Unpack<'a>)>,
},
Named(&'a ast::ExprNamed),
Comprehension {
@ -2092,12 +1986,37 @@ enum CurrentAssignment<'a> {
},
WithItem {
item: &'a ast::WithItem,
first: bool,
is_async: bool,
unpack: Option<Unpack<'a>>,
unpack: Option<(UnpackPosition, Unpack<'a>)>,
},
}
impl<'a> CurrentAssignment<'a> {
fn unpack(&self) -> Option<Unpack<'a>> {
match self {
Self::Assign { unpack, .. }
| Self::For { unpack, .. }
| Self::WithItem { unpack, .. } => unpack.map(|(_, unpack)| unpack),
Self::AnnAssign(_)
| Self::AugAssign(_)
| Self::Named(_)
| Self::Comprehension { .. } => None,
}
}
fn unpack_position_mut(&mut self) -> Option<&mut UnpackPosition> {
match self {
Self::Assign { unpack, .. }
| Self::For { unpack, .. }
| Self::WithItem { unpack, .. } => unpack.as_mut().map(|(position, _)| position),
Self::AnnAssign(_)
| Self::AugAssign(_)
| Self::Named(_)
| Self::Comprehension { .. } => None,
}
}
}
impl<'a> From<&'a ast::StmtAnnAssign> for CurrentAssignment<'a> {
fn from(value: &'a ast::StmtAnnAssign) -> Self {
Self::AnnAssign(value)
@ -2140,3 +2059,47 @@ impl<'a> CurrentMatchCase<'a> {
Self { pattern, index: 0 }
}
}
enum Unpackable<'a> {
Assign(&'a ast::StmtAssign),
For(&'a ast::StmtFor),
WithItem {
item: &'a ast::WithItem,
is_async: bool,
},
}
impl<'a> Unpackable<'a> {
const fn kind(&self) -> UnpackKind {
match self {
Unpackable::Assign(_) => UnpackKind::Assign,
Unpackable::For(_) => UnpackKind::Iterable,
Unpackable::WithItem { .. } => UnpackKind::ContextManager,
}
}
fn as_current_assignment(&self, unpack: Option<Unpack<'a>>) -> CurrentAssignment<'a> {
let unpack = unpack.map(|unpack| (UnpackPosition::First, unpack));
match self {
Unpackable::Assign(stmt) => CurrentAssignment::Assign { node: stmt, unpack },
Unpackable::For(stmt) => CurrentAssignment::For { node: stmt, unpack },
Unpackable::WithItem { item, is_async } => CurrentAssignment::WithItem {
item,
is_async: *is_async,
unpack,
},
}
}
fn as_attribute_assignment(&self, expression: Expression<'a>) -> AttributeAssignment<'a> {
match self {
Unpackable::Assign(_) => AttributeAssignment::Unannotated { value: expression },
Unpackable::For(_) => AttributeAssignment::Iterable {
iterable: expression,
},
Unpackable::WithItem { .. } => AttributeAssignment::ContextManager {
context_manager: expression,
},
}
}
}

View file

@ -8,7 +8,7 @@ use ruff_text_size::{Ranged, TextRange};
use crate::ast_node_ref::AstNodeRef;
use crate::node_key::NodeKey;
use crate::semantic_index::symbol::{FileScopeId, ScopeId, ScopedSymbolId};
use crate::unpack::Unpack;
use crate::unpack::{Unpack, UnpackPosition};
use crate::Db;
/// A definition of a symbol.
@ -239,27 +239,24 @@ pub(crate) struct ImportFromDefinitionNodeRef<'a> {
#[derive(Copy, Clone, Debug)]
pub(crate) struct AssignmentDefinitionNodeRef<'a> {
pub(crate) unpack: Option<Unpack<'a>>,
pub(crate) unpack: Option<(UnpackPosition, Unpack<'a>)>,
pub(crate) value: &'a ast::Expr,
pub(crate) name: &'a ast::ExprName,
pub(crate) first: bool,
}
#[derive(Copy, Clone, Debug)]
pub(crate) struct WithItemDefinitionNodeRef<'a> {
pub(crate) unpack: Option<Unpack<'a>>,
pub(crate) unpack: Option<(UnpackPosition, Unpack<'a>)>,
pub(crate) context_expr: &'a ast::Expr,
pub(crate) name: &'a ast::ExprName,
pub(crate) first: bool,
pub(crate) is_async: bool,
}
#[derive(Copy, Clone, Debug)]
pub(crate) struct ForStmtDefinitionNodeRef<'a> {
pub(crate) unpack: Option<Unpack<'a>>,
pub(crate) unpack: Option<(UnpackPosition, Unpack<'a>)>,
pub(crate) iterable: &'a ast::Expr,
pub(crate) name: &'a ast::ExprName,
pub(crate) first: bool,
pub(crate) is_async: bool,
}
@ -332,12 +329,10 @@ impl<'db> DefinitionNodeRef<'db> {
unpack,
value,
name,
first,
}) => DefinitionKind::Assignment(AssignmentDefinitionKind {
target: TargetKind::from(unpack),
value: AstNodeRef::new(parsed.clone(), value),
name: AstNodeRef::new(parsed, name),
first,
}),
DefinitionNodeRef::AnnotatedAssignment(assign) => {
DefinitionKind::AnnotatedAssignment(AstNodeRef::new(parsed, assign))
@ -349,13 +344,11 @@ impl<'db> DefinitionNodeRef<'db> {
unpack,
iterable,
name,
first,
is_async,
}) => DefinitionKind::For(ForStmtDefinitionKind {
target: TargetKind::from(unpack),
iterable: AstNodeRef::new(parsed.clone(), iterable),
name: AstNodeRef::new(parsed, name),
first,
is_async,
}),
DefinitionNodeRef::Comprehension(ComprehensionDefinitionNodeRef {
@ -382,13 +375,11 @@ impl<'db> DefinitionNodeRef<'db> {
unpack,
context_expr,
name,
first,
is_async,
}) => DefinitionKind::WithItem(WithItemDefinitionKind {
target: TargetKind::from(unpack),
context_expr: AstNodeRef::new(parsed.clone(), context_expr),
name: AstNodeRef::new(parsed, name),
first,
is_async,
}),
DefinitionNodeRef::MatchPattern(MatchPatternDefinitionNodeRef {
@ -451,7 +442,6 @@ impl<'db> DefinitionNodeRef<'db> {
value: _,
unpack: _,
name,
first: _,
}) => name.into(),
Self::AnnotatedAssignment(node) => node.into(),
Self::AugmentedAssignment(node) => node.into(),
@ -459,7 +449,6 @@ impl<'db> DefinitionNodeRef<'db> {
unpack: _,
iterable: _,
name,
first: _,
is_async: _,
}) => name.into(),
Self::Comprehension(ComprehensionDefinitionNodeRef { target, .. }) => target.into(),
@ -469,7 +458,6 @@ impl<'db> DefinitionNodeRef<'db> {
Self::WithItem(WithItemDefinitionNodeRef {
unpack: _,
context_expr: _,
first: _,
is_async: _,
name,
}) => name.into(),
@ -652,14 +640,14 @@ impl DefinitionKind<'_> {
#[derive(Copy, Clone, Debug, PartialEq, Hash)]
pub(crate) enum TargetKind<'db> {
Sequence(Unpack<'db>),
Sequence(UnpackPosition, Unpack<'db>),
Name,
}
impl<'db> From<Option<Unpack<'db>>> for TargetKind<'db> {
fn from(value: Option<Unpack<'db>>) -> Self {
impl<'db> From<Option<(UnpackPosition, Unpack<'db>)>> for TargetKind<'db> {
fn from(value: Option<(UnpackPosition, Unpack<'db>)>) -> Self {
match value {
Some(unpack) => TargetKind::Sequence(unpack),
Some((unpack_position, unpack)) => TargetKind::Sequence(unpack_position, unpack),
None => TargetKind::Name,
}
}
@ -780,7 +768,6 @@ pub struct AssignmentDefinitionKind<'db> {
target: TargetKind<'db>,
value: AstNodeRef<ast::Expr>,
name: AstNodeRef<ast::ExprName>,
first: bool,
}
impl<'db> AssignmentDefinitionKind<'db> {
@ -795,10 +782,6 @@ impl<'db> AssignmentDefinitionKind<'db> {
pub(crate) fn name(&self) -> &ast::ExprName {
self.name.node()
}
pub(crate) fn is_first(&self) -> bool {
self.first
}
}
#[derive(Clone, Debug)]
@ -806,7 +789,6 @@ pub struct WithItemDefinitionKind<'db> {
target: TargetKind<'db>,
context_expr: AstNodeRef<ast::Expr>,
name: AstNodeRef<ast::ExprName>,
first: bool,
is_async: bool,
}
@ -823,10 +805,6 @@ impl<'db> WithItemDefinitionKind<'db> {
self.name.node()
}
pub(crate) const fn is_first(&self) -> bool {
self.first
}
pub(crate) const fn is_async(&self) -> bool {
self.is_async
}
@ -837,7 +815,6 @@ pub struct ForStmtDefinitionKind<'db> {
target: TargetKind<'db>,
iterable: AstNodeRef<ast::Expr>,
name: AstNodeRef<ast::ExprName>,
first: bool,
is_async: bool,
}
@ -854,10 +831,6 @@ impl<'db> ForStmtDefinitionKind<'db> {
self.name.node()
}
pub(crate) const fn is_first(&self) -> bool {
self.first
}
pub(crate) const fn is_async(&self) -> bool {
self.is_async
}

View file

@ -84,7 +84,7 @@ use crate::types::{
UnionType,
};
use crate::types::{CallableType, GeneralCallableType, Signature};
use crate::unpack::Unpack;
use crate::unpack::{Unpack, UnpackPosition};
use crate::util::subscript::{PyIndex, PySlice};
use crate::Db;
@ -1823,10 +1823,10 @@ impl<'db> TypeInferenceBuilder<'db> {
todo_type!("async `with` statement")
} else {
match with_item.target() {
TargetKind::Sequence(unpack) => {
TargetKind::Sequence(unpack_position, unpack) => {
let unpacked = infer_unpack_types(self.db(), unpack);
let name_ast_id = name.scoped_expression_id(self.db(), self.scope());
if with_item.is_first() {
if unpack_position == UnpackPosition::First {
self.context.extend(unpacked);
}
unpacked.expression_type(name_ast_id)
@ -2627,11 +2627,11 @@ impl<'db> TypeInferenceBuilder<'db> {
let value_ty = self.infer_standalone_expression(value);
let mut target_ty = match assignment.target() {
TargetKind::Sequence(unpack) => {
TargetKind::Sequence(unpack_position, unpack) => {
let unpacked = infer_unpack_types(self.db(), unpack);
// Only copy the diagnostics if this is the first assignment to avoid duplicating the
// unpack assignments.
if assignment.is_first() {
if unpack_position == UnpackPosition::First {
self.context.extend(unpacked);
}
@ -2929,9 +2929,9 @@ impl<'db> TypeInferenceBuilder<'db> {
todo_type!("async iterables/iterators")
} else {
match for_stmt.target() {
TargetKind::Sequence(unpack) => {
TargetKind::Sequence(unpack_position, unpack) => {
let unpacked = infer_unpack_types(self.db(), unpack);
if for_stmt.is_first() {
if unpack_position == UnpackPosition::First {
self.context.extend(unpacked);
}
let name_ast_id = name.scoped_expression_id(self.db(), self.scope());

View file

@ -8,7 +8,7 @@ use ruff_python_ast::{self as ast, AnyNodeRef};
use crate::semantic_index::ast_ids::{HasScopedExpressionId, ScopedExpressionId};
use crate::semantic_index::symbol::ScopeId;
use crate::types::{infer_expression_types, todo_type, Type, TypeCheckDiagnostics};
use crate::unpack::UnpackValue;
use crate::unpack::{UnpackKind, UnpackValue};
use crate::Db;
use super::context::{InferContext, WithDiagnostics};
@ -45,30 +45,27 @@ impl<'db> Unpacker<'db> {
let value_type = infer_expression_types(self.db(), value.expression())
.expression_type(value.scoped_expression_id(self.db(), self.scope));
let value_type = match value {
UnpackValue::Assign(expression) => {
let value_type = match value.kind() {
UnpackKind::Assign => {
if self.context.in_stub()
&& expression.node_ref(self.db()).is_ellipsis_literal_expr()
&& value
.expression()
.node_ref(self.db())
.is_ellipsis_literal_expr()
{
Type::unknown()
} else {
value_type
}
}
UnpackValue::Iterable(_) => value_type.try_iterate(self.db()).unwrap_or_else(|err| {
UnpackKind::Iterable => value_type.try_iterate(self.db()).unwrap_or_else(|err| {
err.report_diagnostic(&self.context, value_type, value.as_any_node_ref(self.db()));
err.fallback_element_type(self.db())
}),
UnpackValue::ContextManager(_) => {
value_type.try_enter(self.db()).unwrap_or_else(|err| {
err.report_diagnostic(
&self.context,
value_type,
value.as_any_node_ref(self.db()),
);
UnpackKind::ContextManager => value_type.try_enter(self.db()).unwrap_or_else(|err| {
err.report_diagnostic(&self.context, value_type, value.as_any_node_ref(self.db()));
err.fallback_enter_type(self.db())
})
}
}),
};
self.unpack_inner(target, value.as_any_node_ref(self.db()), value_type);

View file

@ -60,23 +60,21 @@ impl<'db> Unpack<'db> {
/// The expression that is being unpacked.
#[derive(Clone, Copy, Debug, Hash, salsa::Update)]
pub(crate) enum UnpackValue<'db> {
/// An iterable expression like the one in a `for` loop or a comprehension.
Iterable(Expression<'db>),
/// An context manager expression like the one in a `with` statement.
ContextManager(Expression<'db>),
/// An expression that is being assigned to a target.
Assign(Expression<'db>),
pub(crate) struct UnpackValue<'db> {
/// The kind of unpack expression
kind: UnpackKind,
/// The expression we are unpacking
expression: Expression<'db>,
}
impl<'db> UnpackValue<'db> {
pub(crate) fn new(kind: UnpackKind, expression: Expression<'db>) -> Self {
Self { kind, expression }
}
/// Returns the underlying [`Expression`] that is being unpacked.
pub(crate) const fn expression(self) -> Expression<'db> {
match self {
UnpackValue::Assign(expr)
| UnpackValue::Iterable(expr)
| UnpackValue::ContextManager(expr) => expr,
}
self.expression
}
/// Returns the [`ScopedExpressionId`] of the underlying expression.
@ -94,4 +92,27 @@ impl<'db> UnpackValue<'db> {
pub(crate) fn as_any_node_ref(self, db: &'db dyn Db) -> AnyNodeRef<'db> {
self.expression().node_ref(db).node().into()
}
pub(crate) const fn kind(self) -> UnpackKind {
self.kind
}
}
#[derive(Clone, Copy, Debug, Hash, salsa::Update)]
pub(crate) enum UnpackKind {
/// An iterable expression like the one in a `for` loop or a comprehension.
Iterable,
/// An context manager expression like the one in a `with` statement.
ContextManager,
/// An expression that is being assigned to a target.
Assign,
}
/// The position of the target element in an unpacking.
#[derive(Clone, Copy, Debug, Hash, PartialEq, salsa::Update)]
pub(crate) enum UnpackPosition {
/// The target element is in the first position of the unpacking.
First,
/// The target element is in the position other than the first position of the unpacking.
Other,
}