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Merged
youknowone merged 5 commits into from
Jan 8, 2026
Merged

Prevent symbol table exhaustion during codegen #6670

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f5c7e39
Initial plan
Copilot Jan 7, 2026
e7879ba
Handle missing symbol table without panic
Copilot Jan 7, 2026
109f15d
Update symbol table error message
Copilot Jan 7, 2026
5121b75
Track symbol table cursors to avoid exhaustion
Copilot Jan 7, 2026
a2d4061
Auto-format: cargo fmt --all
github-actions[bot] Jan 7, 2026
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71 changes: 31 additions & 40 deletions crates/codegen/src/compile.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -637,25 +637,29 @@ impl Compiler {
}

/// Push the next symbol table on to the stack
fn push_symbol_table(&mut self) -> &SymbolTable {
fn push_symbol_table(&mut self) -> CompileResult<&SymbolTable> {
// Look up the next table contained in the scope of the current table
let current_table = self
.symbol_table_stack
.last_mut()
.expect("no current symbol table");

if current_table.sub_tables.is_empty() {
panic!(
"push_symbol_table: no sub_tables available in {} (type: {:?})",
current_table.name, current_table.typ
);
if current_table.next_sub_table >= current_table.sub_tables.len() {
let name = current_table.name.clone();
let typ = current_table.typ;
return Err(self.error(CodegenErrorType::SyntaxError(format!(
"no symbol table available in {} (type: {:?})",
name, typ
))));
}

let table = current_table.sub_tables.remove(0);
let idx = current_table.next_sub_table;
current_table.next_sub_table += 1;
let table = current_table.sub_tables[idx].clone();

// Push the next table onto the stack
self.symbol_table_stack.push(table);
self.current_symbol_table()
Ok(self.current_symbol_table())
}

/// Pop the current symbol table off the stack
Expand Down Expand Up @@ -853,9 +857,9 @@ impl Compiler {
arg_count: u32,
kwonlyarg_count: u32,
obj_name: String,
) {
) -> CompileResult<()> {
// First push the symbol table
let table = self.push_symbol_table();
let table = self.push_symbol_table()?;
let scope_type = table.typ;

// The key is the current position in the symbol table stack
Expand All @@ -865,11 +869,7 @@ impl Compiler {
let lineno = self.get_source_line_number().get();

// Call enter_scope which does most of the work
if let Err(e) = self.enter_scope(&obj_name, scope_type, key, lineno.to_u32()) {
// In the current implementation, push_output doesn't return an error,
// so we panic here. This maintains the same behavior.
panic!("enter_scope failed: {e:?}");
}
self.enter_scope(&obj_name, scope_type, key, lineno.to_u32())?;

// Override the values that push_output sets explicitly
// enter_scope sets default values based on scope_type, but push_output
Expand All @@ -880,6 +880,7 @@ impl Compiler {
info.metadata.posonlyargcount = posonlyarg_count;
info.metadata.kwonlyargcount = kwonlyarg_count;
}
Ok(())
}

// compiler_exit_scope
Expand Down Expand Up @@ -1984,7 +1985,7 @@ impl Compiler {

if let Some(type_params) = type_params {
// For TypeAlias, we need to use push_symbol_table to properly handle the TypeAlias scope
self.push_symbol_table();
self.push_symbol_table()?;

// Compile type params and push to stack
self.compile_type_params(type_params)?;
Expand Down Expand Up @@ -2067,7 +2068,7 @@ impl Compiler {
(parameters.posonlyargs.len() + parameters.args.len()).to_u32(),
parameters.kwonlyargs.len().to_u32(),
name.to_owned(),
);
)?;

let args_iter = core::iter::empty()
.chain(&parameters.posonlyargs)
Expand Down Expand Up @@ -2113,7 +2114,7 @@ impl Compiler {
allow_starred: bool,
) -> CompileResult<()> {
// Push the next symbol table onto the stack
self.push_symbol_table();
self.push_symbol_table()?;

// Get the current symbol table
let key = self.symbol_table_stack.len() - 1;
Expand Down Expand Up @@ -2332,13 +2333,8 @@ impl Compiler {

// Snapshot sub_tables before first finally compilation
// This allows us to restore them for the second compilation (exception path)
let sub_tables_snapshot = if !finalbody.is_empty() && finally_except_block.is_some() {
Some(
self.symbol_table_stack
.last()
.map(|t| t.sub_tables.clone())
.unwrap_or_default(),
)
let sub_table_cursor = if !finalbody.is_empty() && finally_except_block.is_some() {
self.symbol_table_stack.last().map(|t| t.next_sub_table)
} else {
None
};
Expand All @@ -2353,10 +2349,10 @@ impl Compiler {

if let Some(finally_except) = finally_except_block {
// Restore sub_tables for exception path compilation
if let Some(snapshot) = sub_tables_snapshot
if let Some(cursor) = sub_table_cursor
&& let Some(current_table) = self.symbol_table_stack.last_mut()
{
current_table.sub_tables = snapshot;
current_table.next_sub_table = cursor;
}

self.switch_to_block(finally_except);
Expand Down Expand Up @@ -2617,13 +2613,8 @@ impl Compiler {
}

// Snapshot sub_tables before first finally compilation (for double compilation issue)
let sub_tables_snapshot = if !finalbody.is_empty() && finally_except_block.is_some() {
Some(
self.symbol_table_stack
.last()
.map(|t| t.sub_tables.clone())
.unwrap_or_default(),
)
let sub_table_cursor = if !finalbody.is_empty() && finally_except_block.is_some() {
self.symbol_table_stack.last().map(|t| t.next_sub_table)
} else {
None
};
Expand All @@ -2642,10 +2633,10 @@ impl Compiler {
// Stack at entry: [lasti, exc] (from exception table with preserve_lasti=true)
if let Some(finally_except) = finally_except_block {
// Restore sub_tables for exception path compilation
if let Some(snapshot) = sub_tables_snapshot
if let Some(cursor) = sub_table_cursor
&& let Some(current_table) = self.symbol_table_stack.last_mut()
{
current_table.sub_tables = snapshot;
current_table.next_sub_table = cursor;
}

self.switch_to_block(finally_except);
Expand Down Expand Up @@ -3246,7 +3237,7 @@ impl Compiler {
num_typeparam_args as u32,
0,
type_params_name,
);
)?;

// Add parameter names to varnames for the type params scope
// These will be passed as arguments when the closure is called
Expand Down Expand Up @@ -3554,7 +3545,7 @@ impl Compiler {
) -> CompileResult<CodeObject> {
// 1. Enter class scope
let key = self.symbol_table_stack.len();
self.push_symbol_table();
self.push_symbol_table()?;
self.enter_scope(name, CompilerScope::Class, key, firstlineno)?;

// Set qualname using the new method
Expand Down Expand Up @@ -3660,7 +3651,7 @@ impl Compiler {
0,
0,
type_params_name,
);
)?;

// Set private name for name mangling
self.code_stack.last_mut().unwrap().private = Some(name.to_owned());
Expand Down Expand Up @@ -6322,7 +6313,7 @@ impl Compiler {
};

// Create magnificent function <listcomp>:
self.push_output(flags, 1, 1, 0, name.to_owned());
self.push_output(flags, 1, 1, 0, name.to_owned())?;

// Mark that we're in an inlined comprehension
self.current_code_info().in_inlined_comp = true;
Expand Down
4 changes: 4 additions & 0 deletions crates/codegen/src/symboltable.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,9 @@ pub struct SymbolTable {
/// AST nodes.
pub sub_tables: Vec<SymbolTable>,

/// Cursor pointing to the next sub-table to consume during compilation.
pub next_sub_table: usize,

/// Variable names in definition order (parameters first, then locals)
pub varnames: Vec<String>,

Expand All @@ -70,6 +73,7 @@ impl SymbolTable {
is_nested,
symbols: IndexMap::default(),
sub_tables: vec![],
next_sub_table: 0,
varnames: Vec::new(),
needs_class_closure: false,
needs_classdict: false,
Expand Down
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