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//! Code for tracking scopes and looking up names as the emitter traverses
//! the program.
//!
//! EmitterScopes exist only while the bytecode emitter is working.
//! Longer-lived scope information is stored in `ScopeDataMap`.
use crate::emitter::InstructionWriter;
use ast::source_atom_set::SourceAtomSetIndex;
use std::collections::HashMap;
use std::iter::Iterator;
use stencil::env_coord::{EnvironmentHops, EnvironmentSlot};
use stencil::frame_slot::FrameSlot;
use stencil::scope::{BindingKind, GlobalScopeData, LexicalScopeData, ScopeDataMap, ScopeIndex};
use stencil::scope_notes::ScopeNoteIndex;
/// Result of looking up a name.
///
/// Corresponds to js::frontend::NameLocation in
/// m-c/js/src/frontend/NameAnalysisTypes.h
#[derive(Debug, Clone)]
pub enum NameLocation {
Dynamic,
Global(BindingKind),
FrameSlot(FrameSlot, BindingKind),
EnvironmentCoord(EnvironmentHops, EnvironmentSlot, BindingKind),
}
#[derive(Debug, Copy, Clone, PartialEq)]
pub struct EmitterScopeDepth {
index: usize,
}
impl EmitterScopeDepth {
fn has_parent(&self) -> bool {
self.index > 0
}
fn parent(&self) -> Self {
debug_assert!(self.has_parent());
Self {
index: self.index - 1,
}
}
}
// --- EmitterScope types
//
// These types are the variants of enum EmitterScope.
#[derive(Debug)]
pub struct GlobalEmitterScope {
cache: HashMap<SourceAtomSetIndex, NameLocation>,
}
impl GlobalEmitterScope {
fn new(data: &GlobalScopeData) -> Self {
let mut cache = HashMap::new();
for item in data.iter() {
cache.insert(item.name(), NameLocation::Global(item.kind()));
}
Self { cache }
}
fn lookup_name(&self, name: SourceAtomSetIndex) -> Option<NameLocation> {
match self.cache.get(&name) {
Some(loc) => Some(loc.clone()),
None => Some(NameLocation::Global(BindingKind::Var)),
}
}
fn next_frame_slot(&self) -> FrameSlot {
FrameSlot::new(0)
}
fn scope_note_index(&self) -> Option<ScopeNoteIndex> {
None
}
fn has_environment_object(&self) -> bool {
false
}
}
struct LexicalEnvironmentObject {}
impl LexicalEnvironmentObject {
fn first_free_slot() -> u32 {
// FIXME: This is the value of
// `JSSLOT_FREE(&LexicalEnvironmentObject::class_)`
// in SpiderMonkey
2
}
}
#[derive(Debug)]
pub struct LexicalEmitterScope {
cache: HashMap<SourceAtomSetIndex, NameLocation>,
next_frame_slot: FrameSlot,
needs_environment_object: bool,
scope_note_index: Option<ScopeNoteIndex>,
}
impl LexicalEmitterScope {
pub fn new(data: &LexicalScopeData, first_frame_slot: FrameSlot) -> Self {
let is_all_bindings_closed_over = data.base.is_all_bindings_closed_over();
let mut needs_environment_object = false;
let mut cache = HashMap::new();
let mut frame_slot = first_frame_slot;
let mut env_slot = EnvironmentSlot::new(LexicalEnvironmentObject::first_free_slot());
for item in data.iter() {
if is_all_bindings_closed_over || item.is_closed_over() {
cache.insert(
item.name(),
NameLocation::EnvironmentCoord(EnvironmentHops::new(0), env_slot, item.kind()),
);
env_slot.next();
needs_environment_object = true;
} else {
cache.insert(
item.name(),
NameLocation::FrameSlot(frame_slot, item.kind()),
);
frame_slot.next();
}
}
Self {
cache,
next_frame_slot: frame_slot,
needs_environment_object,
scope_note_index: None,
}
}
fn lookup_name(&self, name: SourceAtomSetIndex) -> Option<NameLocation> {
match self.cache.get(&name) {
Some(loc) => Some(loc.clone()),
None => None,
}
}
fn next_frame_slot(&self) -> FrameSlot {
self.next_frame_slot
}
fn scope_note_index(&self) -> Option<ScopeNoteIndex> {
self.scope_note_index
}
pub fn has_environment_object(&self) -> bool {
self.needs_environment_object
}
}
/// The information about a scope needed for emitting bytecode.
#[derive(Debug)]
pub enum EmitterScope {
Global(GlobalEmitterScope),
Lexical(LexicalEmitterScope),
}
impl EmitterScope {
fn lookup_name(&self, name: SourceAtomSetIndex) -> Option<NameLocation> {
match self {
EmitterScope::Global(scope) => scope.lookup_name(name),
EmitterScope::Lexical(scope) => scope.lookup_name(name),
}
}
fn next_frame_slot(&self) -> FrameSlot {
match self {
EmitterScope::Global(scope) => scope.next_frame_slot(),
EmitterScope::Lexical(scope) => scope.next_frame_slot(),
}
}
pub fn scope_note_index(&self) -> Option<ScopeNoteIndex> {
match self {
EmitterScope::Global(scope) => scope.scope_note_index(),
EmitterScope::Lexical(scope) => scope.scope_note_index(),
}
}
fn has_environment_object(&self) -> bool {
match self {
EmitterScope::Global(scope) => scope.has_environment_object(),
EmitterScope::Lexical(scope) => scope.has_environment_object(),
}
}
fn is_var_scope(&self) -> bool {
match self {
EmitterScope::Global(_) => true,
EmitterScope::Lexical(_) => false,
}
}
}
/// Stack that tracks the current scope chain while emitting bytecode.
///
/// Bytecode is emitted by traversing the structure of the program. During this
/// process there's always a "current position". This stack represents the
/// scope chain at the current position. It is updated when we enter or leave
/// any node that has its own scope.
///
/// Unlike the C++ impl, this uses an explicit stack struct, since Rust cannot
/// store a reference to a stack-allocated object in another object that has a
/// longer lifetime.
pub struct EmitterScopeStack {
scope_stack: Vec<EmitterScope>,
}
impl EmitterScopeStack {
/// Create a new, empty scope stack.
pub fn new() -> Self {
Self {
scope_stack: Vec::new(),
}
}
/// The current innermost scope.
fn innermost(&self) -> &EmitterScope {
self.scope_stack
.last()
.expect("There should be at least one scope")
}
/// Enter the global scope. Call this once at the beginning of a top-level
/// script.
///
/// This emits bytecode that implements parts of [ScriptEvaluation][1] and
/// [GlobalDeclarationInstantiation][2].
///
pub fn enter_global(
&mut self,
emit: &mut InstructionWriter,
scope_data_map: &ScopeDataMap,
top_level_function_count: u32,
) {
let scope_index = scope_data_map.get_global_index();
let scope_data = scope_data_map.get_global_at(scope_index);
// The outermost scope should be the first item in the GC things list.
// Enter global scope here, before emitting any name ops below.
emit.enter_global_scope(scope_index);
if scope_data.base.bindings.len() > 0 {
emit.global_or_eval_decl_instantiation(top_level_function_count);
}
emit.switch_to_main();
let scope = EmitterScope::Global(GlobalEmitterScope::new(scope_data));
self.scope_stack.push(scope);
}
/// Leave the global scope. Call this once at the end of a top-level
/// script.
pub fn leave_global(&mut self, emit: &InstructionWriter) {
match self.scope_stack.pop() {
Some(EmitterScope::Global(_)) => {}
_ => panic!("unmatching scope"),
}
emit.leave_global_scope();
}
/// Emit bytecode to mark some local lexical variables as uninitialized.
fn dead_zone_frame_slot_range(
&self,
emit: &mut InstructionWriter,
slot_start: FrameSlot,
slot_end: FrameSlot,
) {
if slot_start == slot_end {
return;
}
emit.uninitialized();
let mut slot = slot_start;
while slot < slot_end {
emit.init_lexical(slot.into());
slot.next();
}
emit.pop();
}
/// Enter a lexical scope.
///
/// A new LexicalEmitterScope based on scope_data_map is pushed to the
/// scope stack. Bytecode is emitted to mark the new lexical bindings as
/// uninitialized.
pub fn enter_lexical(
&mut self,
emit: &mut InstructionWriter,
scope_data_map: &mut ScopeDataMap,
scope_index: ScopeIndex,
) {
let mut scope_data = scope_data_map.get_lexical_at_mut(scope_index);
let parent_scope_note_index = self.innermost().scope_note_index();
let first_frame_slot = self.innermost().next_frame_slot();
scope_data.first_frame_slot = first_frame_slot;
let mut lexical_scope = LexicalEmitterScope::new(scope_data, first_frame_slot);
let next_frame_slot = lexical_scope.next_frame_slot;
let index = emit.enter_lexical_scope(
scope_index,
parent_scope_note_index,
next_frame_slot,
lexical_scope.needs_environment_object,
);
lexical_scope.scope_note_index = Some(index);
let scope = EmitterScope::Lexical(lexical_scope);
self.scope_stack.push(scope);
self.dead_zone_frame_slot_range(emit, first_frame_slot, next_frame_slot);
}
/// Leave a lexical scope.
pub fn leave_lexical(&mut self, emit: &mut InstructionWriter) {
let lexical_scope = match self.scope_stack.pop() {
Some(EmitterScope::Lexical(scope)) => scope,
_ => panic!("unmatching scope"),
};
emit.leave_lexical_scope(
lexical_scope
.scope_note_index
.expect("scope note index should be populated"),
lexical_scope.needs_environment_object,
);
}
/// Resolve a name by searching the current scope chain.
///
/// Implements the parts of [ResolveBinding][1] that can be done at
/// emit time.
///
pub fn lookup_name(&mut self, name: SourceAtomSetIndex) -> NameLocation {
let mut hops = EnvironmentHops::new(0);
for scope in self.scope_stack.iter().rev() {
if let Some(loc) = scope.lookup_name(name) {
return match loc {
NameLocation::EnvironmentCoord(orig_hops, slot, kind) => {
debug_assert!(u8::from(orig_hops) == 0u8);
NameLocation::EnvironmentCoord(hops, slot, kind)
}
_ => loc,
};
}
if scope.has_environment_object() {
hops.next();
}
}
NameLocation::Dynamic
}
/// Just like lookup_name, but only in var scope.
pub fn lookup_name_in_var(&mut self, name: SourceAtomSetIndex) -> NameLocation {
let mut hops = EnvironmentHops::new(0);
for scope in self.scope_stack.iter().rev() {
if scope.is_var_scope() {
if let Some(loc) = scope.lookup_name(name) {
return match loc {
NameLocation::EnvironmentCoord(orig_hops, slot, kind) => {
debug_assert!(u8::from(orig_hops) == 0u8);
NameLocation::EnvironmentCoord(hops, slot, kind)
}
_ => loc,
};
}
}
if scope.has_environment_object() {
hops.next();
}
}
NameLocation::Dynamic
}
pub fn current_depth(&self) -> EmitterScopeDepth {
EmitterScopeDepth {
index: self.scope_stack.len() - 1,
}
}
/// Walk the scope stack up to and including `to` depth.
/// See EmitterScopeWalker for the details.
pub fn walk_up_to_including<'a>(&'a self, to: EmitterScopeDepth) -> EmitterScopeWalker<'a> {
EmitterScopeWalker::new(self, to)
}
pub fn get_current_scope_note_index(&self) -> Option<ScopeNoteIndex> {
self.innermost().scope_note_index()
}
fn get<'a>(&'a self, index: EmitterScopeDepth) -> &'a EmitterScope {
self.scope_stack
.get(index.index)
.expect("scope should exist")
}
}
/// Walk the scope stack up to `to`, and yields EmitterScopeWalkItem for
/// each scope.
///
/// The first item is `{ outer: parent-of-innermost, inner: innermost }`, and
/// the last item is `{ outer: to, inner: child-of-to }`.
pub struct EmitterScopeWalker<'a> {
stack: &'a EmitterScopeStack,
to: EmitterScopeDepth,
current: EmitterScopeDepth,
}
impl<'a> EmitterScopeWalker<'a> {
fn new(stack: &'a EmitterScopeStack, to: EmitterScopeDepth) -> Self {
let current = stack.current_depth();
Self { stack, to, current }
}
}
pub struct EmitterScopeWalkItem<'a> {
pub outer: &'a EmitterScope,
pub inner: &'a EmitterScope,
}
impl<'a> Iterator for EmitterScopeWalker<'a> {
type Item = EmitterScopeWalkItem<'a>;
fn next(&mut self) -> Option<EmitterScopeWalkItem<'a>> {
if self.current == self.to {
return None;
}
let outer_index = self.current.parent();
let inner_index = self.current;
self.current = outer_index;
Some(EmitterScopeWalkItem {
inner: self.stack.get(inner_index),
outer: self.stack.get(outer_index),
})
}
}