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use std::collections::HashSet;
use ecow::eco_format;
use typst_library::diag::{bail, error, At, SourceDiagnostic, SourceResult};
use typst_library::foundations::{Array, Dict, Value};
use typst_syntax::ast::{self, AstNode};
use crate::{Access, Eval, Vm};
impl Eval for ast::LetBinding<'_> {
type Output = Value;
fn eval(self, vm: &mut Vm) -> SourceResult<Self::Output> {
let value = match self.init() {
Some(expr) => expr.eval(vm)?,
None => Value::None,
};
if vm.flow.is_some() {
return Ok(Value::None);
}
match self.kind() {
ast::LetBindingKind::Normal(pattern) => destructure(vm, pattern, value)?,
ast::LetBindingKind::Closure(ident) => vm.define(ident, value),
}
Ok(Value::None)
}
}
impl Eval for ast::DestructAssignment<'_> {
type Output = Value;
fn eval(self, vm: &mut Vm) -> SourceResult<Self::Output> {
let value = self.value().eval(vm)?;
destructure_impl(vm, self.pattern(), value, &mut |vm, expr, value| {
let location = expr.access(vm)?;
*location = value;
Ok(())
})?;
Ok(Value::None)
}
}
/// Destructures a value into a pattern.
pub(crate) fn destructure(
vm: &mut Vm,
pattern: ast::Pattern,
value: Value,
) -> SourceResult<()> {
destructure_impl(vm, pattern, value, &mut |vm, expr, value| match expr {
ast::Expr::Ident(ident) => {
vm.define(ident, value);
Ok(())
}
_ => bail!(expr.span(), "cannot assign to this expression"),
})
}
/// Destruct the given value into the pattern and apply the function to each binding.
fn destructure_impl<F>(
vm: &mut Vm,
pattern: ast::Pattern,
value: Value,
f: &mut F,
) -> SourceResult<()>
where
F: Fn(&mut Vm, ast::Expr, Value) -> SourceResult<()>,
{
match pattern {
ast::Pattern::Normal(expr) => f(vm, expr, value)?,
ast::Pattern::Placeholder(_) => {}
ast::Pattern::Parenthesized(parenthesized) => {
destructure_impl(vm, parenthesized.pattern(), value, f)?
}
ast::Pattern::Destructuring(destruct) => match value {
Value::Array(value) => destructure_array(vm, destruct, value, f)?,
Value::Dict(value) => destructure_dict(vm, destruct, value, f)?,
_ => bail!(pattern.span(), "cannot destructure {}", value.ty()),
},
}
Ok(())
}
fn destructure_array<F>(
vm: &mut Vm,
destruct: ast::Destructuring,
value: Array,
f: &mut F,
) -> SourceResult<()>
where
F: Fn(&mut Vm, ast::Expr, Value) -> SourceResult<()>,
{
let len = value.as_slice().len();
let mut i = 0;
for p in destruct.items() {
match p {
ast::DestructuringItem::Pattern(pattern) => {
let Ok(v) = value.at(i as i64, None) else {
bail!(wrong_number_of_elements(destruct, len));
};
destructure_impl(vm, pattern, v, f)?;
i += 1;
}
ast::DestructuringItem::Spread(spread) => {
let sink_size = (1 + len).checked_sub(destruct.items().count());
let sink = sink_size.and_then(|s| value.as_slice().get(i..i + s));
let (Some(sink_size), Some(sink)) = (sink_size, sink) else {
bail!(wrong_number_of_elements(destruct, len));
};
if let Some(expr) = spread.sink_expr() {
f(vm, expr, Value::Array(sink.into()))?;
}
i += sink_size;
}
ast::DestructuringItem::Named(named) => {
bail!(named.span(), "cannot destructure named pattern from an array")
}
}
}
if i < len {
bail!(wrong_number_of_elements(destruct, len));
}
Ok(())
}
fn destructure_dict<F>(
vm: &mut Vm,
destruct: ast::Destructuring,
dict: Dict,
f: &mut F,
) -> SourceResult<()>
where
F: Fn(&mut Vm, ast::Expr, Value) -> SourceResult<()>,
{
let mut sink = None;
let mut used = HashSet::new();
for p in destruct.items() {
match p {
// Shorthand for a direct identifier.
ast::DestructuringItem::Pattern(ast::Pattern::Normal(ast::Expr::Ident(
ident,
))) => {
let v = dict.get(&ident).at(ident.span())?;
f(vm, ast::Expr::Ident(ident), v.clone())?;
used.insert(ident.get().clone());
}
ast::DestructuringItem::Named(named) => {
let name = named.name();
let v = dict.get(&name).at(name.span())?;
destructure_impl(vm, named.pattern(), v.clone(), f)?;
used.insert(name.get().clone());
}
ast::DestructuringItem::Spread(spread) => sink = spread.sink_expr(),
ast::DestructuringItem::Pattern(expr) => {
bail!(expr.span(), "cannot destructure unnamed pattern from dictionary");
}
}
}
if let Some(expr) = sink {
let mut sink = Dict::new();
for (key, value) in dict {
if !used.contains(key.as_str()) {
sink.insert(key, value);
}
}
f(vm, expr, Value::Dict(sink))?;
}
Ok(())
}
/// The error message when the number of elements of the destructuring and the
/// array is mismatched.
#[cold]
fn wrong_number_of_elements(
destruct: ast::Destructuring,
len: usize,
) -> SourceDiagnostic {
let mut count = 0;
let mut spread = false;
for p in destruct.items() {
match p {
ast::DestructuringItem::Pattern(_) => count += 1,
ast::DestructuringItem::Spread(_) => spread = true,
ast::DestructuringItem::Named(_) => {}
}
}
let quantifier = if len > count { "too many" } else { "not enough" };
let expected = match (spread, count) {
(true, 1) => "at least 1 element".into(),
(true, c) => eco_format!("at least {c} elements"),
(false, 0) => "an empty array".into(),
(false, 1) => "a single element".into(),
(false, c) => eco_format!("{c} elements",),
};
error!(
destruct.span(), "{quantifier} elements to destructure";
hint: "the provided array has a length of {len}, \
but the pattern expects {expected}",
)
}
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