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vm: count derivation string-coercion against max-call-depth #8

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52 changes: 52 additions & 0 deletions src/expr/eval/tests/derivation.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -416,6 +416,58 @@ test "evaluate minimal derivation builtins" {
try std.testing.expectEqualStrings("1", preserved_args);
}

test "deeply nested derivation argument values evaluate" {
var ev = try Engine.init(std.testing.allocator, .{ .worker_count = 0 });
defer ev.deinit();
var source: std.ArrayListUnmanaged(u8) = .empty;
defer source.deinit(std.testing.allocator);
try source.appendSlice(std.testing.allocator, "let deep = ");
for (0..2000) |_| try source.appendSlice(std.testing.allocator, "[ ");
try source.append(std.testing.allocator, '1');
for (0..2000) |_| try source.appendSlice(std.testing.allocator, " ]");
try source.appendSlice(std.testing.allocator,
\\; in (builtins.derivation {
\\ name = "d";
\\ system = "x86_64-linux";
\\ builder = ":";
\\ attr = deep;
\\}).drvPath
);
_ = try ev.evaluate(source.items);
}

test "derivation builtin rejects self-referential argument values" {
var list_ev = try Engine.init(std.testing.allocator, .{ .worker_count = 0 });
defer list_ev.deinit();
try std.testing.expectError(
error.CallDepthExceeded,
list_ev.evaluate(
\\let r = [ r ];
\\in (builtins.derivation {
\\ name = "d";
\\ system = "x86_64-linux";
\\ builder = ":";
\\ attr = r;
\\}).drvPath
),
);

var attrs_ev = try Engine.init(std.testing.allocator, .{ .worker_count = 0 });
defer attrs_ev.deinit();
try std.testing.expectError(
error.CallDepthExceeded,
attrs_ev.evaluate(
\\let r = { outPath = r; };
\\in (builtins.derivation {
\\ name = "d";
\\ system = "x86_64-linux";
\\ builder = ":";
\\ attr = r;
\\}).drvPath
),
);
}

test "derivation builtin rejects missing required attrs" {
try std.testing.expectError(
error.MissingAttribute,
Expand Down
31 changes: 26 additions & 5 deletions src/expr/vm/builtins/strings.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -433,6 +433,19 @@ pub fn coerceAttrsToStringValue(self: *VM, attrs: Value) !Value {
}

pub fn coerceDerivationStringValue(self: *VM, arg: Value) !Value {
return coerceDerivationStringValueDepth(self, arg, 0);
}

/// Nix counts coercion recursion against the same `max-call-depth` budget
/// as function calls (`EvalState::coerceToString` takes a `CallDepth`
/// level), so a self-referential value errs like a runaway call chain and
/// `--option max-call-depth` governs both.
fn coerceDerivationStringValueDepth(self: *VM, arg: Value, depth: u32) anyerror!Value {
if (depth > self.policy.max_call_depth) return vm_trace.callDepthExceeded(self);
// Native backstop, same as forceThunkImpl: the logical budget can
// exceed what the running stack holds.
if (@frameAddress() < self.executionContextConst().stack_limit)
return vm_trace.stackOverflow(self);
const value = try vm_force.forceValue(self, arg);
switch (value.kind()) {
.string, .string_context, .heap_string => return value,
Expand All @@ -452,13 +465,17 @@ pub fn coerceDerivationStringValue(self: *VM, arg: Value) !Value {
},
.bool_false, .null => return Value.string(try self.intern.intern("")),
.bool_true => return Value.string(try self.intern.intern("1")),
.list => return coerceDerivationListToStringValue(self, value.asObjectId()),
.attrs => return coerceDerivationAttrsToStringValue(self, value),
.list => return coerceDerivationListToStringValueDepth(self, value.asObjectId(), depth),
.attrs => return coerceDerivationAttrsToStringValueDepth(self, value, depth),
else => return error.TypeError,
}
}

pub fn coerceDerivationListToStringValue(self: *VM, list_id: ObjectId) !Value {
return coerceDerivationListToStringValueDepth(self, list_id, 0);
}

fn coerceDerivationListToStringValueDepth(self: *VM, list_id: ObjectId, depth: u32) anyerror!Value {
// GC: root the (bare-id) list across the recursive force-walk.
const gc_roots = vm_force.rootsBegin(self);
defer vm_force.rootsEnd(self, gc_roots);
Expand Down Expand Up @@ -487,7 +504,7 @@ pub fn coerceDerivationListToStringValue(self: *VM, list_id: ObjectId) !Value {
if (!first) try out.append(self.allocator, ' ');
first = false;
trailing_empty_list = false;
const item_value = try coerceDerivationStringValue(self, forced);
const item_value = try coerceDerivationStringValueDepth(self, forced, depth + 1);
// GC: `item_value` may be a FRESH context string (nested-list/attrs
// coercion) held only in this Zig local — not the rooted list arg.
// `appendContextEntry` forces (context merge) and can collect; root
Expand All @@ -507,13 +524,17 @@ pub fn coerceDerivationListToStringValue(self: *VM, list_id: ObjectId) !Value {
}

pub fn coerceDerivationAttrsToStringValue(self: *VM, attrs: Value) !Value {
return coerceDerivationAttrsToStringValueDepth(self, attrs, 0);
}

fn coerceDerivationAttrsToStringValueDepth(self: *VM, attrs: Value, depth: u32) anyerror!Value {
const gc_roots = vm_force.rootsBegin(self);
defer vm_force.rootsEnd(self, gc_roots);
vm_force.rootKeep(self, attrs); // held across getAttrValue + callValue + coerce
const to_string_id = try self.intern.intern("__toString");
if (self.heap.getAttrValue(attrs.asObjectId(), to_string_id)) |to_string| {
const result = try vm_closures.callValue(self, try vm_force.forceValue(self, to_string), attrs);
return coerceDerivationStringValue(self, result);
return coerceDerivationStringValueDepth(self, result, depth + 1);
} else |err| switch (err) {
error.MissingAttribute => {},
else => return err,
Expand All @@ -524,5 +545,5 @@ pub fn coerceDerivationAttrsToStringValue(self: *VM, attrs: Value) !Value {
error.MissingAttribute => return error.TypeError,
else => return err,
};
return coerceDerivationStringValue(self, out_path);
return coerceDerivationStringValueDepth(self, out_path, depth + 1);
}