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Fix stack overflow in desugarer via depth limit #1318

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Fix stack overflow in desugarer via depth limit #1318

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114 changes: 60 additions & 54 deletions core/desugarer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -228,12 +228,14 @@ class Desugarer {
public:
Desugarer(Allocator *alloc, bool isStdlib = false) : alloc(alloc), isStdlib(isStdlib) {}

void desugarParams(ArgParams &params, unsigned obj_level)
static constexpr unsigned MAX_DESUGAR_DEPTH = 500;

void desugarParams(ArgParams &params, unsigned obj_level, unsigned depth)
{
for (auto &param : params) {
if (param.expr) {
// Default arg.
desugar(param.expr, obj_level);
desugar(param.expr, obj_level, depth);
}
}
}
Expand All @@ -242,16 +244,16 @@ class Desugarer {
// If self occurs, also map the self identifier to nullptr.
typedef std::vector<std::pair<const Identifier *, AST *>> SuperVars;

SuperVars desugarFields(AST *ast, ObjectFields &fields, unsigned obj_level)
SuperVars desugarFields(AST *ast, ObjectFields &fields, unsigned obj_level, unsigned depth)
{
// Desugar children
for (auto &field : fields) {
if (field.expr1 != nullptr)
desugar(field.expr1, obj_level);
desugar(field.expr2, obj_level + 1);
desugar(field.expr1, obj_level, depth);
desugar(field.expr2, obj_level + 1, depth);
if (field.expr3 != nullptr)
desugar(field.expr3, obj_level + 1);
desugarParams(field.params, obj_level + 1);
desugar(field.expr3, obj_level + 1, depth);
desugarParams(field.params, obj_level + 1, depth);
}

// Simplify asserts
Expand Down Expand Up @@ -583,15 +585,15 @@ class Desugarer {
return in;
}

AST* makeObject(Object *ast, unsigned obj_level) {
AST* makeObject(Object *ast, unsigned obj_level, unsigned depth) {
// Hidden variable to allow outer/top binding.
if (obj_level == 0) {
const Identifier *hidden_var = id(U"$");
auto *body = make<Self>(E, EF);
ast->fields.push_back(ObjectField::Local(EF, EF, hidden_var, EF, body, EF));
}

SuperVars svs = desugarFields(ast, ast->fields, obj_level);
SuperVars svs = desugarFields(ast, ast->fields, obj_level, depth);

DesugaredObject::Fields new_fields;
ASTs new_asserts;
Expand Down Expand Up @@ -624,15 +626,15 @@ class Desugarer {
return retval;
}

AST* makeObjectComprehension(ObjectComprehension *ast, unsigned obj_level) {
AST* makeObjectComprehension(ObjectComprehension *ast, unsigned obj_level, unsigned depth) {
// Hidden variable to allow outer/top binding.
if (obj_level == 0) {
const Identifier *hidden_var = id(U"$");
auto *body = make<Self>(E, EF);
ast->fields.push_back(ObjectField::Local(EF, EF, hidden_var, EF, body, EF));
}

SuperVars svs = desugarFields(ast, ast->fields, obj_level);
SuperVars svs = desugarFields(ast, ast->fields, obj_level, depth);

AST *field = ast->fields.front().expr1;
AST *value = ast->fields.front().expr2;
Expand Down Expand Up @@ -673,7 +675,7 @@ class Desugarer {
false,
ast->specs,
EF);
desugar(arr, obj_level);
desugar(arr, obj_level, depth);
return make<ObjectComprehensionSimple>(
ast->location,
make<Index>(E, EF, var(_arr), EF, false, zero, EF, nullptr, EF, nullptr, EF),
Expand All @@ -682,46 +684,50 @@ class Desugarer {
arr);
}

void desugar(AST *&ast_, unsigned obj_level)
void desugar(AST *&ast_, unsigned obj_level, unsigned depth = 0)
{
if (depth > MAX_DESUGAR_DEPTH) {
throw StaticError(ast_->location,
"Maximum expression nesting depth exceeded during desugaring.");
}
if (auto *ast = dynamic_cast<Apply *>(ast_)) {
desugar(ast->target, obj_level);
desugar(ast->target, obj_level, depth + 1);
for (ArgParam &arg : ast->args)
desugar(arg.expr, obj_level);
desugar(arg.expr, obj_level, depth + 1);

} else if (auto *ast = dynamic_cast<ApplyBrace *>(ast_)) {
desugar(ast->left, obj_level);
desugar(ast->right, obj_level);
desugar(ast->left, obj_level, depth + 1);
desugar(ast->right, obj_level, depth + 1);
ast_ =
make<Binary>(ast->location, ast->openFodder, ast->left, EF, BOP_PLUS, ast->right);

} else if (auto *ast = dynamic_cast<Array *>(ast_)) {
for (auto &el : ast->elements)
desugar(el.expr, obj_level);
desugar(el.expr, obj_level, depth + 1);

} else if (auto *ast = dynamic_cast<ArrayComprehension *>(ast_)) {
for (ComprehensionSpec &spec : ast->specs)
desugar(spec.expr, obj_level);
desugar(ast->body, obj_level + 1);
desugar(spec.expr, obj_level, depth + 1);
desugar(ast->body, obj_level + 1, depth + 1);

ast_ = makeArrayComprehension(ast);

} else if (auto *ast = dynamic_cast<Assert *>(ast_)) {
desugar(ast->cond, obj_level);
desugar(ast->cond, obj_level, depth + 1);
if (ast->message == nullptr) {
ast->message = str(U"Assertion failed.");
}
desugar(ast->message, obj_level);
desugar(ast->rest, obj_level);
desugar(ast->message, obj_level, depth + 1);
desugar(ast->rest, obj_level, depth + 1);

// if cond then rest else error msg
AST *branch_false = make<Error>(ast->location, EF, ast->message);
ast_ = make<Conditional>(
ast->location, ast->openFodder, ast->cond, EF, ast->rest, EF, branch_false);

} else if (auto *ast = dynamic_cast<Binary *>(ast_)) {
desugar(ast->left, obj_level);
desugar(ast->right, obj_level);
desugar(ast->left, obj_level, depth + 1);
desugar(ast->right, obj_level, depth + 1);

bool invert = false;

Expand Down Expand Up @@ -750,11 +756,11 @@ class Desugarer {
// Nothing to do.

} else if (auto *ast = dynamic_cast<Conditional *>(ast_)) {
desugar(ast->cond, obj_level);
desugar(ast->branchTrue, obj_level);
desugar(ast->cond, obj_level, depth + 1);
desugar(ast->branchTrue, obj_level, depth + 1);
if (ast->branchFalse == nullptr)
ast->branchFalse = null();
desugar(ast->branchFalse, obj_level);
desugar(ast->branchFalse, obj_level, depth + 1);

} else if (auto *ast = dynamic_cast<Dollar *>(ast_)) {
if (obj_level == 0) {
Expand All @@ -763,47 +769,47 @@ class Desugarer {
ast_ = var(id(U"$"));

} else if (auto *ast = dynamic_cast<Error *>(ast_)) {
desugar(ast->expr, obj_level);
desugar(ast->expr, obj_level, depth + 1);

} else if (auto *ast = dynamic_cast<Function *>(ast_)) {
desugar(ast->body, obj_level);
desugarParams(ast->params, obj_level);
desugar(ast->body, obj_level, depth + 1);
desugarParams(ast->params, obj_level, depth + 1);

} else if (auto *ast = dynamic_cast<Import *>(ast_)) {
// TODO(dcunnin): Abstract this into a template function if it becomes more common.
AST *file = ast->file;
desugar(file, obj_level);
desugar(file, obj_level, depth + 1);
ast->file = dynamic_cast<LiteralString *>(file);

} else if (auto *ast = dynamic_cast<Importstr *>(ast_)) {
// TODO(dcunnin): Abstract this into a template function if it becomes more common.
AST *file = ast->file;
desugar(file, obj_level);
desugar(file, obj_level, depth + 1);
ast->file = dynamic_cast<LiteralString *>(file);

} else if (auto *ast = dynamic_cast<Importbin *>(ast_)) {
// TODO(dcunnin): Abstract this into a template function if it becomes more common.
AST *file = ast->file;
desugar(file, obj_level);
desugar(file, obj_level, depth + 1);
ast->file = dynamic_cast<LiteralString *>(file);

} else if (auto *ast = dynamic_cast<InSuper *>(ast_)) {
desugar(ast->element, obj_level);
desugar(ast->element, obj_level, depth + 1);

} else if (auto *ast = dynamic_cast<Index *>(ast_)) {
desugar(ast->target, obj_level);
desugar(ast->target, obj_level, depth + 1);
if (ast->isSlice) {
if (ast->index == nullptr)
ast->index = null();
desugar(ast->index, obj_level);
desugar(ast->index, obj_level, depth + 1);

if (ast->end == nullptr)
ast->end = null();
desugar(ast->end, obj_level);
desugar(ast->end, obj_level, depth + 1);

if (ast->step == nullptr)
ast->step = null();
desugar(ast->step, obj_level);
desugar(ast->step, obj_level, depth + 1);

ast_ = make<Apply>(
ast->location,
Expand All @@ -828,17 +834,17 @@ class Desugarer {
ast->index = str(ast->id->name);
ast->id = nullptr;
}
desugar(ast->index, obj_level);
desugar(ast->index, obj_level, depth + 1);
}

} else if (auto *ast = dynamic_cast<Local *>(ast_)) {
for (auto &bind : ast->binds)
desugar(bind.body, obj_level);
desugar(ast->body, obj_level);
desugar(bind.body, obj_level, depth + 1);
desugar(ast->body, obj_level, depth + 1);

for (auto &bind : ast->binds) {
if (bind.functionSugar) {
desugarParams(bind.params, obj_level);
desugarParams(bind.params, obj_level, depth + 1);
bind.body = make<Function>(ast->location,
ast->openFodder,
bind.parenLeftFodder,
Expand Down Expand Up @@ -872,27 +878,27 @@ class Desugarer {

} else if (auto *ast = dynamic_cast<DesugaredObject *>(ast_)) {
for (auto &field : ast->fields) {
desugar(field.name, obj_level);
desugar(field.body, obj_level + 1);
desugar(field.name, obj_level, depth + 1);
desugar(field.body, obj_level + 1, depth + 1);
}
for (AST *assert : ast->asserts) {
desugar(assert, obj_level + 1);
desugar(assert, obj_level + 1, depth + 1);
}

} else if (auto *ast = dynamic_cast<Object *>(ast_)) {
ast_ = makeObject(ast, obj_level);
ast_ = makeObject(ast, obj_level, depth + 1);

} else if (auto *ast = dynamic_cast<ObjectComprehension *>(ast_)) {
ast_ = makeObjectComprehension(ast, obj_level);
ast_ = makeObjectComprehension(ast, obj_level, depth + 1);

} else if (auto *ast = dynamic_cast<ObjectComprehensionSimple *>(ast_)) {
desugar(ast->field, obj_level);
desugar(ast->value, obj_level + 1);
desugar(ast->array, obj_level);
desugar(ast->field, obj_level, depth + 1);
desugar(ast->value, obj_level + 1, depth + 1);
desugar(ast->array, obj_level, depth + 1);

} else if (auto *ast = dynamic_cast<Parens *>(ast_)) {
// Strip parens.
desugar(ast->expr, obj_level);
desugar(ast->expr, obj_level, depth + 1);
ast_ = ast->expr;

} else if (dynamic_cast<const Self *>(ast_)) {
Expand All @@ -904,10 +910,10 @@ class Desugarer {
ast->index = str(ast->id->name);
ast->id = nullptr;
}
desugar(ast->index, obj_level);
desugar(ast->index, obj_level, depth + 1);

} else if (auto *ast = dynamic_cast<Unary *>(ast_)) {
desugar(ast->expr, obj_level);
desugar(ast->expr, obj_level, depth + 1);

} else if (dynamic_cast<const Var *>(ast_)) {
// Nothing to do.
Expand Down