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//! This module contains the [`ValidationStack`] data structure
//!
//! The [`ValidationStack`] is a unified stack, in the sense that it unifies both
//! [`ValidationStackEntry::Val`] and [`ValidationStackEntry::Label`]. It therefore mixes type
//! information with structured control flow information.
#![allow(unused)] // TODO remove this once sidetable implementation lands
use super::Result;
use alloc::vec::Vec;
use crate::{Error, ValType};
#[derive(Debug, PartialEq, Eq)]
pub(super) struct ValidationStack {
stack: Vec<ValidationStackEntry>,
}
impl ValidationStack {
/// Initialize a new ValidationStack
pub(super) fn new() -> Self {
Self { stack: Vec::new() }
}
pub(super) fn len(&self) -> usize {
self.stack.len()
}
pub(super) fn push_valtype(&mut self, valtype: ValType) {
self.stack.push(ValidationStackEntry::Val(valtype));
}
pub(super) fn push_label(&mut self, label_info: LabelInfo) {
self.stack.push(ValidationStackEntry::Label(label_info));
}
/// This puts an unspecified element on top of the stack.
/// While the top of the stack is unspecified, arbitrary value types can be popped.
/// To undo this, a new label has to be pushed or an existing one has to be popped.
///
/// See the documentation for [`ValidationStackEntry::UnspecifiedValTypes`] for more info.
pub(super) fn make_unspecified(&mut self) {
// Pop everything until next label or until the stack is empty.
// This is okay, because these values cannot be accessed during execution ever again.
while let Some(entry) = self.stack.last() {
match entry {
ValidationStackEntry::Val(_) | ValidationStackEntry::UnspecifiedValTypes => {
self.stack.pop();
}
ValidationStackEntry::Label(_) => break,
}
}
self.stack.push(ValidationStackEntry::UnspecifiedValTypes)
}
/// Pop a [`ValidationStackEntry`] from the [`ValidationStack`]
///
/// # Returns
///
/// - Returns `Ok(_)` with the former top-most [`ValidationStackEntry`] inside, if the stack had
/// at least one element.
/// - Returns `Err(_)` if the stack was already empty.
fn pop(&mut self) -> Result<ValidationStackEntry> {
self.stack
.pop()
.ok_or(Error::InvalidValidationStackValType(None))
}
/// Assert the top-most [`ValidationStackEntry`] is a specific [`ValType`], after popping it from the [`ValidationStack`]
///
/// # Returns
///
/// - Returns `Ok(())` if the top-most [`ValidationStackEntry`] is a [`ValType`] identical to
/// `expected_ty`.
/// - Returns `Err(_)` otherwise.
pub(super) fn assert_pop_val_type(&mut self, expected_ty: ValType) -> Result<()> {
if let Some(ValidationStackEntry::UnspecifiedValTypes) = self.stack.last() {
// An unspecified value is always correct, and will never disappear by popping.
return Ok(());
}
match self.pop()? {
ValidationStackEntry::Val(ty) => (ty == expected_ty)
.then_some(())
.ok_or(Error::InvalidValidationStackValType(Some(ty))),
ValidationStackEntry::Label(li) => Err(Error::FoundLabel(li.kind)),
ValidationStackEntry::UnspecifiedValTypes => {
unreachable!("we just checked if the topmost entry is of this type")
}
}
}
/// Asserts that the values on top of the stack match those of a value iterator
///
/// The last element of `expected_val_types` is compared to the top-most
/// [`ValidationStackEntry`], the second last `expected_val_types` element to the second top-most
/// [`ValidationStackEntry`] etc.
///
/// Any occurence of the [`ValidationStackEntry::Label`] variant in the stack tail will cause an
/// error. This method does not mutate the [`ValidationStack::stack`] in any way.
///
/// # Returns
///
/// - `Ok(_)`, the tail of the stack matches the `expected_val_types`
/// - `Err(_)` otherwise
pub(super) fn assert_val_types_on_top(&self, expected_val_types: &[ValType]) -> Result<()> {
let stack_tail = self
.stack
.get(self.stack.len() - expected_val_types.len()..)
.ok_or(Error::InvalidValType)?;
// Now we check the valtypes in reverse.
// That way we can stop checking if we encounter an `UnspecifiedValTypes`.
let mut current_expected_valtype = expected_val_types.iter().rev();
for entry in stack_tail.iter().rev() {
match entry {
ValidationStackEntry::Label(label) => return Err(Error::EndInvalidValueStack),
ValidationStackEntry::Val(valtype) => {
if Some(valtype) != current_expected_valtype.next() {
return Err(Error::EndInvalidValueStack);
}
}
ValidationStackEntry::UnspecifiedValTypes => {
// In case we find an `UnspecifiedValTypes`, we pretend that all expected valtypes are found.
// That's because this entry can expand to every possible combination of valtypes.
return Ok(());
}
}
}
Ok(())
}
/// Asserts that the valtypes on the stack match the expected valtypes.
///
/// This starts by comparing the top-most valtype with the last element from `expected_val_types` and then continues downwards on the stack.
/// If a label is reached and not all `expected_val_types` have been checked, the assertion fails.
///
/// # Returns
///
/// - `Ok(())` if all expected valtypes were found
/// - `Err(_)` otherwise
pub(super) fn assert_val_types(&self, expected_val_types: &[ValType]) -> Result<()> {
let topmost_label_index = self.find_topmost_label_idx();
let first_valtype = topmost_label_index.map(|idx| idx + 1).unwrap_or(0);
// Now we check the valtypes in reverse.
// That way we can stop checking if we encounter an `UnspecifiedValTypes`.
let mut current_expected_valtype = expected_val_types.iter().rev();
for entry in self.stack[first_valtype..].iter().rev() {
match entry {
ValidationStackEntry::Label(_) => unreachable!(
"we started at the top-most label so we cannot find any more labels"
),
ValidationStackEntry::Val(valtype) => {
if Some(valtype) != current_expected_valtype.next() {
return Err(Error::EndInvalidValueStack);
}
}
ValidationStackEntry::UnspecifiedValTypes => {
return Ok(());
}
}
}
Ok(())
}
/// A helper to find the index of the top-most label in [`ValidationStack::stack`]
fn find_topmost_label_idx(&self) -> Option<usize> {
self.stack
.iter()
.enumerate()
.rev()
.find(|(_idx, entry)| matches!(entry, ValidationStackEntry::Label(_)))
.map(|(idx, _entry)| idx)
}
/// Searches for the top-most label, then pops the label and all entry on top of that label.
/// Only the label's [`LabelInfo`] is returned.
///
/// # Returns
///
/// - `Ok(LabelInfo)` if a label has been found and popped
/// - `None` if no label was found on the stack
fn pop_label_and_above(&mut self) -> Option<LabelInfo> {
/// Delete all the values until the topmost label or until the stack is empty
match self.find_topmost_label_idx() {
Some(idx) => {
if self.stack.len() > idx + 1 {
self.stack.drain((idx + 1)..);
}
}
None => self.stack.clear(),
}
// Pop the label itself
match self.pop() {
Ok(ValidationStackEntry::Label(info)) => Some(info),
Ok(_) => unreachable!(
"we just removed everything until the next label, thus new topmost entry must be a label"
),
Err(_) => None,
}
}
/// Return true if the stack has at least one remaining label
pub(super) fn has_remaining_label(&self) -> bool {
self.stack
.iter()
.any(|e| matches!(e, ValidationStackEntry::Label(_)))
}
}
#[derive(Clone, Debug, PartialEq, Eq)]
enum ValidationStackEntry {
/// A value
Val(ValType),
/// A label
Label(LabelInfo),
/// Special variant to encode that any possible number of [`ValType`]s could be here
///
/// Caused by `return` and `unreachable`, as both can push an arbitrary number of values to the stack.
///
/// When this variant is pushed onto the stack, all valtypes until the next lower label are deleted.
/// They are not needed anymore because this variant can expand to all of them.
UnspecifiedValTypes,
}
#[derive(Clone, Debug, PartialEq, Eq)]
pub(crate) struct LabelInfo {
pub(crate) kind: LabelKind,
}
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum LabelKind {
Block,
Loop,
If,
}
#[cfg(test)]
mod tests {
use crate::{NumType, RefType, ValType};
use super::{LabelInfo, LabelKind, ValidationStack};
#[test]
fn push_then_pop() {
let mut stack = ValidationStack::new();
stack.push_valtype(ValType::NumType(NumType::F64));
stack.push_valtype(ValType::NumType(NumType::I32));
stack.push_valtype(ValType::VecType);
stack.push_valtype(ValType::RefType(RefType::ExternRef));
stack
.assert_pop_val_type(ValType::RefType(RefType::ExternRef))
.unwrap();
stack.assert_pop_val_type(ValType::VecType).unwrap();
stack
.assert_pop_val_type(ValType::NumType(NumType::I32))
.unwrap();
stack
.assert_pop_val_type(ValType::NumType(NumType::F64))
.unwrap();
}
#[test]
fn labels() {
let mut stack = ValidationStack::new();
stack.push_valtype(ValType::NumType(NumType::I64));
stack.push_label(LabelInfo {
kind: LabelKind::Block,
});
stack.push_label(LabelInfo {
kind: LabelKind::Loop,
});
stack.push_valtype(ValType::VecType);
// This removes the `ValType::VecType` and the `LabelKind::Loop` label
let popped_label = stack.pop_label_and_above().unwrap();
assert_eq!(
popped_label,
LabelInfo {
kind: LabelKind::Loop,
}
);
let popped_label = stack.pop_label_and_above().unwrap();
assert_eq!(
popped_label,
LabelInfo {
kind: LabelKind::Block,
}
);
// The first valtype should still be there
stack.assert_pop_val_type(ValType::NumType(NumType::I64));
}
#[test]
fn assert_valtypes() {
let mut stack = ValidationStack::new();
stack.push_valtype(ValType::NumType(NumType::F64));
stack.push_valtype(ValType::NumType(NumType::I32));
stack.push_valtype(ValType::NumType(NumType::F32));
stack
.assert_val_types(&[
ValType::NumType(NumType::F64),
ValType::NumType(NumType::I32),
ValType::NumType(NumType::F32),
])
.unwrap();
stack.push_label(LabelInfo {
kind: LabelKind::Block,
});
stack.push_valtype(ValType::NumType(NumType::I32));
stack
.assert_val_types(&[ValType::NumType(NumType::I32)])
.unwrap();
}
#[test]
fn assert_emtpy_valtypes() {
let mut stack = ValidationStack::new();
stack.assert_val_types(&[]).unwrap();
stack.push_valtype(ValType::NumType(NumType::I32));
stack.push_label(LabelInfo {
kind: LabelKind::Block,
});
// Valtypes separated by a label should also not be detected
stack.assert_val_types(&[]).unwrap();
}
#[test]
fn assert_valtypes_on_top() {
let mut stack = ValidationStack::new();
stack.assert_val_types_on_top(&[]).unwrap();
stack.push_valtype(ValType::NumType(NumType::I32));
stack.push_valtype(ValType::NumType(NumType::F32));
stack.push_valtype(ValType::NumType(NumType::I64));
// There are always zero valtypes on top of the stack
stack.assert_val_types_on_top(&[]).unwrap();
stack
.assert_val_types_on_top(&[ValType::NumType(NumType::I64)])
.unwrap();
stack
.assert_val_types_on_top(&[
ValType::NumType(NumType::F32),
ValType::NumType(NumType::I64),
])
.unwrap();
stack
.assert_val_types_on_top(&[
ValType::NumType(NumType::I32),
ValType::NumType(NumType::F32),
ValType::NumType(NumType::I64),
])
.unwrap();
}
#[test]
fn unspecified() {
let mut stack = ValidationStack::new();
stack.push_label(LabelInfo {
kind: LabelKind::Block,
});
stack.make_unspecified();
// Now we can pop as many valtypes from the stack as we want
stack
.assert_pop_val_type(ValType::NumType(NumType::I32))
.unwrap();
stack
.assert_pop_val_type(ValType::RefType(RefType::ExternRef))
.unwrap();
// Let's remove the unspecified entry and the first label
let popped_label = stack.pop_label_and_above().unwrap();
assert_eq!(
popped_label,
LabelInfo {
kind: LabelKind::Block,
}
);
// Now there are no values left on the stack
assert_eq!(stack.assert_val_types(&[]), Ok(()));
}
}