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Fix sub_table ordering for nested inlined comprehensions (PEP 709) #7480

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Merged
youknowone merged 1 commit into from
Mar 22, 2026
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Merged

Fix sub_table ordering for nested inlined comprehensions (PEP 709) #7480

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18 changes: 13 additions & 5 deletions crates/codegen/src/compile.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8013,23 +8013,31 @@ impl Compiler {
) -> CompileResult<()> {
// PEP 709: Consume the comprehension's sub_table.
// The symbols are already merged into parent scope by analyze_symbol_table.
// Splice the comprehension's children into the parent so nested scopes
// (e.g. inner comprehensions, lambdas) can be found by the compiler.
let current_table = self
.symbol_table_stack
.last_mut()
.expect("no current symbol table");
let comp_table = current_table.sub_tables[current_table.next_sub_table].clone();
current_table.next_sub_table += 1;

// Compile the outermost iterator first. Its expression may reference
// nested scopes (e.g. lambdas) whose sub_tables sit at the current
// position in the parent's list. Those must be consumed before we
// splice in the comprehension's own children.
self.compile_expression(&generators[0].iter)?;

// Splice the comprehension's children (e.g. nested inlined
// comprehensions) into the parent so the compiler can find them.
if !comp_table.sub_tables.is_empty() {
let current_table = self
.symbol_table_stack
.last_mut()
.expect("no current symbol table");
let insert_pos = current_table.next_sub_table;
for (i, st) in comp_table.sub_tables.iter().enumerate() {
current_table.sub_tables.insert(insert_pos + i, st.clone());
}
}

// Step 1: Compile the outermost iterator BEFORE tweaking scopes
self.compile_expression(&generators[0].iter)?;
if has_async && generators[0].is_async {
emit!(self, Instruction::GetAIter);
} else {
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34 changes: 34 additions & 0 deletions extra_tests/snippets/syntax_comprehension.py
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Original file line number Diff line number Diff line change
Expand Up @@ -45,3 +45,37 @@
def f():
# Test no panic occurred.
[[x := 1 for j in range(5)] for i in range(5)]


# Nested inlined comprehensions with lambda in the first iterator expression.
# The lambda's sub_table must be consumed before the inner comprehension's
# sub_table is spliced in, otherwise scope ordering is wrong.
def test_nested_comp_with_lambda():
import itertools
offsets = {0: [0], 1: [1], 3: [2]}
grouped = [
[x for _, x in group]
for _, group in itertools.groupby(
enumerate(sorted(offsets.keys())), lambda x: x[1] - x[0]
)
]
assert grouped == [[0, 1], [3]], f"got {grouped}"

test_nested_comp_with_lambda()


# Nested inlined comprehensions with throwaway `_` in both levels.
def test_nested_comp_underscore():
data = [(1, "a", "x"), (2, "b", "y")]
result = [[v for _, v in zip(range(2), row)] for _, *row in data]
assert result == [["a", "x"], ["b", "y"]], f"got {result}"

test_nested_comp_underscore()


# Simple nested inlined comprehensions.
def test_simple_nested_comp():
result = [[j * i for j in range(3)] for i in range(3)]
assert result == [[0, 0, 0], [0, 1, 2], [0, 2, 4]]

test_simple_nested_comp()
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