Fix "tried to pop from empty stack" with BlockExpr and const

im-0 · im-0 · commit 239ff886578a · 2026-05-18T20:59:26.000+02:00
Constant expressions without side effects are optimized away unless in an interactive mode[1]. This causes panic when last statement in a block is a constant and Mode::BlockExpr is used as this constant value must be returned to caller. Example panic: ---- vm::python_run::tests::test_block_expr_return_const stdout ---- [crates/vm/src/frame.rs:9653:9] self = ExecutingFrame { code: code: <code object <module> at ??? file "<embedded>", line 1>, stack_len: 0, } thread 'vm::python_run::tests::test_block_expr_return_const' (2640752) panicked at crates/vm/src/frame.rs:9410:18: tried to pop from empty stack stack backtrace: 0: __rustc::rust_begin_unwind at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/std/src/panicking.rs:689:5 1: core::panicking::panic_fmt at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/core/src/panicking.rs:80:14 2: rustpython_vm::frame::ExecutingFrame::fatal at ./src/frame.rs:9654:9 3: rustpython_vm::frame::ExecutingFrame::pop_stackref_opt at ./src/frame.rs:9410:18 4: rustpython_vm::frame::ExecutingFrame::pop_stackref at ./src/frame.rs:9420:18 5: rustpython_vm::frame::ExecutingFrame::pop_value at ./src/frame.rs:9435:14 6: rustpython_vm::frame::ExecutingFrame::execute_instruction at ./src/frame.rs:3391:34 7: rustpython_vm::frame::ExecutingFrame::run at ./src/frame.rs:1623:31 8: rustpython_vm::frame::<impl rustpython_vm::object::core::Py<rustpython_vm::frame::Frame>>::run::{{closure}} at ./src/frame.rs:1098:44 9: rustpython_vm::frame::<impl rustpython_vm::object::core::Py<rustpython_vm::frame::Frame>>::with_exec at ./src/frame.rs:1093:9 10: rustpython_vm::frame::<impl rustpython_vm::object::core::Py<rustpython_vm::frame::Frame>>::run at ./src/frame.rs:1098:14 11: rustpython_vm::vm::VirtualMachine::run_frame::{{closure}} at ./src/vm/mod.rs:1201:44 12: rustpython_vm::vm::VirtualMachine::with_frame_impl::{{closure}}::{{closure}} at ./src/vm/mod.rs:1610:60 13: rustpython_vm::vm::VirtualMachine::dispatch_traced_frame at ./src/vm/mod.rs:1689:22 14: rustpython_vm::vm::VirtualMachine::with_frame_impl::{{closure}} at ./src/vm/mod.rs:1610:22 15: rustpython_vm::vm::VirtualMachine::with_recursion at ./src/vm/mod.rs:1547:9 16: rustpython_vm::vm::VirtualMachine::with_frame_impl at ./src/vm/mod.rs:1572:14 17: rustpython_vm::vm::VirtualMachine::with_frame at ./src/vm/mod.rs:1555:14 18: rustpython_vm::vm::VirtualMachine::run_frame at ./src/vm/mod.rs:1201:20 19: rustpython_vm::vm::VirtualMachine::run_code_obj at ./src/vm/mod.rs:1120:14 20: rustpython_vm::vm::python_run::<impl rustpython_vm::vm::VirtualMachine>::run_block_expr at ./src/vm/python_run.rs:51:14 21: rustpython_vm::vm::python_run::tests::test_block_expr_return_const::{{closure}} at ./src/vm/python_run.rs:190:47 22: rustpython_vm::vm::interpreter::Interpreter::enter::{{closure}} at ./src/vm/interpreter.rs:366:39 23: rustpython_vm::vm::thread::set_current_vm::{{closure}} at ./src/vm/thread.rs:107:9 24: std::thread::local::LocalKey<T>::try_with at /home/im/.rustup/toolchains/stable-aarch64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/thread/local.rs:513:12 25: std::thread::local::LocalKey<T>::with at /home/im/.rustup/toolchains/stable-aarch64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/thread/local.rs:477:20 26: rustpython_vm::vm::thread::set_current_vm at ./src/vm/thread.rs:102:14 27: rustpython_vm::vm::thread::enter_vm at ./src/vm/thread.rs:132:5 28: rustpython_vm::vm::interpreter::Interpreter::enter at ./src/vm/interpreter.rs:366:9 29: rustpython_vm::vm::python_run::tests::test_block_expr_return_const at ./src/vm/python_run.rs:188:23 30: rustpython_vm::vm::python_run::tests::test_block_expr_return_const::{{closure}} at ./src/vm/python_run.rs:187:38 31: core::ops::function::FnOnce::call_once at /home/im/.rustup/toolchains/stable-aarch64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:250:5 32: <fn() -> core::result::Result<(), alloc::string::String> as core::ops::function::FnOnce<()>>::call_once at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/core/src/ops/function.rs:250:5 [1] https://github.com/RustPython/RustPython/blob/883ce9d273db98b435eb3f51128925a1255ba88d/crates/codegen/src/compile.rs#L2990-L2997
diff --git a/crates/codegen/src/compile.rs b/crates/codegen/src/compile.rs
@@ -2499,8 +2499,12 @@ impl Compiler {
 
         if let Some(last_statement) = body.last() {
             match last_statement {
-                ast::Stmt::Expr(_) => {
-                    self.current_block().instructions.pop(); // pop Instruction::PopTop
+                ast::Stmt::Expr(ast::StmtExpr { value, .. }) => {
+                    if !self.interactive && Self::is_const_expression(value) {
+                        self.compile_expression(value)?;
+                    } else {
+                        self.current_block().instructions.pop(); // pop Instruction::PopTop
+                    }
                 }
                 ast::Stmt::FunctionDef(_) | ast::Stmt::ClassDef(_) => {
                     let pop_instructions = self.current_block().instructions.pop();
