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starlark: Disallow positional arguments after keyword arguments #40

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Merged
robinlinden merged 1 commit into from
Apr 19, 2026
+20 −11
Merged

starlark: Disallow positional arguments after keyword arguments #40

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7 changes: 7 additions & 0 deletions starlark/parser.h
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Original file line number Diff line number Diff line change
Expand Up @@ -347,6 +347,7 @@ class Parser {

std::optional<std::vector<Argument>> parse_argument_list() {
std::vector<Argument> args;
bool seen_kw_arg = false;

while (true) {
auto maybe_token = next_token();
Expand Down Expand Up @@ -391,6 +392,7 @@ class Parser {
}

if (std::holds_alternative<token::Equals>(*next)) {
seen_kw_arg = true;
name = Identifier{.name = std::move(ident->name)};

auto value_token = next_token();
Expand All @@ -414,6 +416,11 @@ class Parser {
reconsume(std::move(*next));
}

if (seen_kw_arg) {
std::cerr << "Positional argument may not follow keyword argument.\n";
return std::nullopt;
}

auto value_expr = parse_expression(token);
if (!value_expr) {
std::cerr << "Failed to parse expression for argument value.\n";
Expand Down
24 changes: 13 additions & 11 deletions starlark/parser_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -65,7 +65,7 @@ int main() {
},
},
{
R"(foo(bar = "baz", "qux"))",
R"(foo("qux", bar = "baz"))",
starlark::Program{
.statements{
starlark::ExpressionStmt{
Expand All @@ -74,14 +74,14 @@ int main() {
.target = std::make_shared<starlark::Expression>(
starlark::Identifier{"foo"}),
.args{
{
starlark::Identifier{"bar"},
starlark::StringLiteral{"baz"},
},
{
std::nullopt,
starlark::StringLiteral{"qux"},
},
{
starlark::Identifier{"bar"},
starlark::StringLiteral{"baz"},
},
},
},
},
Expand All @@ -90,7 +90,7 @@ int main() {
},
},
{
R"(foo(bar = baz, qux()))",
R"(foo(qux(), bar = baz))",
starlark::Program{
.statements{
starlark::ExpressionStmt{
Expand All @@ -99,10 +99,6 @@ int main() {
.target = std::make_shared<starlark::Expression>(
starlark::Identifier{"foo"}),
.args{
{
starlark::Identifier{"bar"},
starlark::Identifier{"baz"},
},
{
std::nullopt,
starlark::CallExpr{
Expand All @@ -111,6 +107,10 @@ int main() {
.args{},
},
},
{
starlark::Identifier{"bar"},
starlark::Identifier{"baz"},
},
},
},
},
Expand Down Expand Up @@ -331,7 +331,9 @@ int main() {
static constexpr auto kExpectedParseFailures = std::to_array<std::string_view>({
// CallExpr
// Missing closing parenthesis.
R"(foo(bar = "baz", "qux")",
R"(foo("qux")",
// Positional argument after kw argument.
R"(foo(bar = baz, qux()))",

// ListExpr
// Tokenization error.
Expand Down