[red-knot] Infer target types for unpacked tuple assignment

crates/red_knot_python_semantic/resources/mdtest/unpacking.md

@@ -0,0 +1,273 @@
+# Unpacking
+
+## Tuple
+
+### Simple tuple
+
+```py
+(a, b, c) = (1, 2, 3)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: Literal[3]
+```
+
+### Simple list
+
+```py
+[a, b, c] = (1, 2, 3)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: Literal[3]
+```
+
+### Simple mixed
+
+```py
+[a, (b, c), d] = (1, (2, 3), 4)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: Literal[3]
+reveal_type(d)  # revealed: Literal[4]
+```
+
+### Multiple assignment
+
+```py
+a, b = c = 1, 2
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: tuple[Literal[1], Literal[2]]
+```
+
+### Nested tuple with unpacking
+
+```py
+(a, (b, c), d) = (1, (2, 3), 4)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: Literal[3]
+reveal_type(d)  # revealed: Literal[4]
+```
+
+### Nested tuple without unpacking
+
+```py
+(a, b, c) = (1, (2, 3), 4)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: tuple[Literal[2], Literal[3]]
+reveal_type(c)  # revealed: Literal[4]
+```
+
+### Uneven unpacking (1)
+
+```py
+# TODO: Add diagnostic (there aren't enough values to unpack)
+(a, b, c) = (1, 2)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+reveal_type(c)  # revealed: Unknown
+```
+
+### Uneven unpacking (2)
+
+```py
+# TODO: Add diagnostic (too many values to unpack)
+(a, b) = (1, 2, 3)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+```
+
+### Starred expression (1)
+
+```py
+# TODO: Add diagnostic (need more values to unpack)
+# TODO: Remove 'not-iterable' diagnostic
+[a, *b, c, d] = (1, 2)  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: Literal[1]
+# TODO: Should be list[Any] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: Literal[2]
+reveal_type(d)  # revealed: Unknown
+```
+
+### Starred expression (2)
+
+```py
+[a, *b, c] = (1, 2)  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: Literal[1]
+# TODO: Should be list[Any] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: Literal[2]
+```
+
+### Starred expression (3)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+[a, *b, c] = (1, 2, 3)  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: Literal[1]
+# TODO: Should be list[int] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: Literal[3]
+```
+
+### Starred expression (4)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+[a, *b, c, d] = (1, 2, 3, 4, 5, 6)  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: Literal[1]
+# TODO: Should be list[int] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: Literal[5]
+reveal_type(d)  # revealed: Literal[6]
+```
+
+### Starred expression (5)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+[a, b, *c] = (1, 2, 3, 4)  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: Literal[2]
+# TODO: Should be list[int] once support for assigning to starred expression is added
+reveal_type(c)  # revealed: @Todo
+```
+
+### Non-iterable unpacking
+
+TODO: Remove duplicate diagnostics. This is happening because for a sequence-like
+assignment target, multiple definitions are created and the inference engine runs
+on each of them which results in duplicate diagnostics.
+
+```py
+# error: "Object of type `Literal[1]` is not iterable"
+# error: "Object of type `Literal[1]` is not iterable"
+a, b = 1
+reveal_type(a)  # revealed: Unknown
+reveal_type(b)  # revealed: Unknown
+```
+
+### Custom iterator unpacking
+
+```py
+class Iterator:
+    def __next__(self) -> int:
+        return 42
+
+
+class Iterable:
+    def __iter__(self) -> Iterator:
+        return Iterator()
+
+
+(a, b) = Iterable()
+reveal_type(a)  # revealed: int
+reveal_type(b)  # revealed: int
+```
+
+### Custom iterator unpacking nested
+
+```py
+class Iterator:
+    def __next__(self) -> int:
+        return 42
+
+
+class Iterable:
+    def __iter__(self) -> Iterator:
+        return Iterator()
+
+
+(a, (b, c), d) = (1, Iterable(), 2)
+reveal_type(a)  # revealed: Literal[1]
+reveal_type(b)  # revealed: int
+reveal_type(c)  # revealed: int
+reveal_type(d)  # revealed: Literal[2]
+```
+
+## String
+
+### Simple unpacking
+
+```py
+a, b = 'ab'
+reveal_type(a)  # revealed: LiteralString
+reveal_type(b)  # revealed: LiteralString
+```
+
+### Uneven unpacking (1)
+
+```py
+# TODO: Add diagnostic (there aren't enough values to unpack)
+a, b, c = 'ab'
+reveal_type(a)  # revealed: LiteralString
+reveal_type(b)  # revealed: LiteralString
+reveal_type(c)  # revealed: Unknown
+```
+
+### Uneven unpacking (2)
+
+```py
+# TODO: Add diagnostic (too many values to unpack)
+a, b = 'abc'
+reveal_type(a)  # revealed: LiteralString
+reveal_type(b)  # revealed: LiteralString
+```
+
+### Starred expression (1)
+
+```py
+# TODO: Add diagnostic (need more values to unpack)
+# TODO: Remove 'not-iterable' diagnostic
+(a, *b, c, d) = "ab"  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: LiteralString
+# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: LiteralString
+reveal_type(d)  # revealed: Unknown
+```
+
+### Starred expression (2)
+
+```py
+(a, *b, c) = "ab"  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: LiteralString
+# TODO: Should be list[Any] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: LiteralString
+```
+
+### Starred expression (3)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+(a, *b, c) = "abc"  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: LiteralString
+# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: LiteralString
+```
+
+### Starred expression (4)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+(a, *b, c, d) = "abcdef"  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: LiteralString
+# TODO: Should be list[LiteralString] once support for assigning to starred expression is added
+reveal_type(b)  # revealed: @Todo
+reveal_type(c)  # revealed: LiteralString
+reveal_type(d)  # revealed: LiteralString
+```
+
+### Starred expression (5)
+
+```py
+# TODO: Remove 'not-iterable' diagnostic
+(a, b, *c) = "abcd"  # error: "Object of type `None` is not iterable"
+reveal_type(a)  # revealed: LiteralString
+reveal_type(b)  # revealed: LiteralString
+# TODO: Should be list[int] once support for assigning to starred expression is added
+reveal_type(c)  # revealed: @Todo
+```

crates/red_knot_python_semantic/src/semantic_index.rs

@@ -994,7 +994,7 @@ class C[T]:
         let ast::Expr::NumberLiteral(ast::ExprNumberLiteral {
             value: ast::Number::Int(num),
             ..
-        }) = &*assignment.assignment().value
+        }) = assignment.value()
         else {
             panic!("should be a number literal")
         };

crates/red_knot_python_semantic/src/semantic_index/builder.rs

@@ -28,8 +28,8 @@ use crate::Db;
 
 use super::constraint::{Constraint, PatternConstraint};
 use super::definition::{
-    DefinitionCategory, ExceptHandlerDefinitionNodeRef, MatchPatternDefinitionNodeRef,
-    WithItemDefinitionNodeRef,
+    AssignmentKind, DefinitionCategory, ExceptHandlerDefinitionNodeRef,
+    MatchPatternDefinitionNodeRef, WithItemDefinitionNodeRef,
 };
 
 pub(super) struct SemanticIndexBuilder<'db> {
@@ -566,11 +566,22 @@ where
                 debug_assert!(self.current_assignment.is_none());
                 self.visit_expr(&node.value);
                 self.add_standalone_expression(&node.value);
-                self.current_assignment = Some(node.into());
-                for target in &node.targets {
+                for (target_index, target) in node.targets.iter().enumerate() {
+                    let kind = match target {
+                        ast::Expr::List(_) | ast::Expr::Tuple(_) => Some(AssignmentKind::Sequence),
+                        ast::Expr::Name(_) => Some(AssignmentKind::Name),
+                        _ => None,
+                    };
+                    if let Some(kind) = kind {
+                        self.current_assignment = Some(CurrentAssignment::Assign {
+                            assignment: node,
+                            target_index,
+                            kind,
+                        });
+                    }
                     self.visit_expr(target);
+                    self.current_assignment = None;
                 }
-                self.current_assignment = None;
             }
             ast::Stmt::AnnAssign(node) => {
                 debug_assert!(self.current_assignment.is_none());
@@ -815,12 +826,18 @@ where
                 let symbol = self.add_symbol(id.clone());
                 if is_definition {
                     match self.current_assignment {
-                        Some(CurrentAssignment::Assign(assignment)) => {
+                        Some(CurrentAssignment::Assign {
+                            assignment,
+                            target_index,
+                            kind,
+                        }) => {
                             self.add_definition(
                                 symbol,
                                 AssignmentDefinitionNodeRef {
                                     assignment,
-                                    target: name_node,
+                                    target_index,
+                                    name: name_node,
+                                    kind,
                                 },
                             );
                         }
@@ -1045,7 +1062,11 @@ where
 
 #[derive(Copy, Clone, Debug)]
 enum CurrentAssignment<'a> {
-    Assign(&'a ast::StmtAssign),
+    Assign {
+        assignment: &'a ast::StmtAssign,
+        target_index: usize,
+        kind: AssignmentKind,
+    },
     AnnAssign(&'a ast::StmtAnnAssign),
     AugAssign(&'a ast::StmtAugAssign),
     For(&'a ast::StmtFor),
@@ -1057,12 +1078,6 @@ enum CurrentAssignment<'a> {
     WithItem(&'a ast::WithItem),
 }
 
-impl<'a> From<&'a ast::StmtAssign> for CurrentAssignment<'a> {
-    fn from(value: &'a ast::StmtAssign) -> Self {
-        Self::Assign(value)
-    }
-}
-
 impl<'a> From<&'a ast::StmtAnnAssign> for CurrentAssignment<'a> {
     fn from(value: &'a ast::StmtAnnAssign) -> Self {
         Self::AnnAssign(value)