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|
//! Transcraber takes a template, like `fn $ident() {}`, a set of bindings like
//! `$ident => foo`, interpolates variables in the template, to get `fn foo() {}`
use ra_syntax::SmolStr;
use crate::{
mbe_expander::{Binding, Bindings, Fragment},
parser::{parse_template, Op, RepeatKind, Separator},
ExpandError,
};
impl Bindings {
fn contains(&self, name: &str) -> bool {
self.inner.contains_key(name)
}
fn get(&self, name: &str, nesting: &[usize]) -> Result<&Fragment, ExpandError> {
let mut b = self.inner.get(name).ok_or_else(|| {
ExpandError::BindingError(format!("could not find binding `{}`", name))
})?;
for &idx in nesting.iter() {
b = match b {
Binding::Fragment(_) => break,
Binding::Nested(bs) => bs.get(idx).ok_or_else(|| {
ExpandError::BindingError(format!("could not find nested binding `{}`", name))
})?,
Binding::Empty => {
return Err(ExpandError::BindingError(format!(
"could not find empty binding `{}`",
name
)))
}
};
}
match b {
Binding::Fragment(it) => Ok(it),
Binding::Nested(_) => Err(ExpandError::BindingError(format!(
"expected simple binding, found nested binding `{}`",
name
))),
Binding::Empty => Err(ExpandError::BindingError(format!(
"expected simple binding, found empty binding `{}`",
name
))),
}
}
}
pub(super) fn transcribe(
template: &tt::Subtree,
bindings: &Bindings,
) -> Result<tt::Subtree, ExpandError> {
assert!(template.delimiter == tt::Delimiter::None);
let mut ctx = ExpandCtx { bindings: &bindings, nesting: Vec::new(), var_expanded: false };
expand_subtree(&mut ctx, template)
}
#[derive(Debug)]
struct ExpandCtx<'a> {
bindings: &'a Bindings,
nesting: Vec<usize>,
var_expanded: bool,
}
fn expand_subtree(ctx: &mut ExpandCtx, template: &tt::Subtree) -> Result<tt::Subtree, ExpandError> {
let mut buf: Vec<tt::TokenTree> = Vec::new();
for op in parse_template(template) {
match op? {
Op::TokenTree(tt @ tt::TokenTree::Leaf(..)) => buf.push(tt.clone()),
Op::TokenTree(tt::TokenTree::Subtree(tt)) => {
let tt = expand_subtree(ctx, tt)?;
buf.push(tt.into());
}
Op::Var { name, kind: _ } => {
let fragment = expand_var(ctx, name)?;
push_fragment(&mut buf, fragment);
}
Op::Repeat { subtree, kind, separator } => {
let fragment = expand_repeat(ctx, subtree, kind, separator)?;
push_fragment(&mut buf, fragment)
}
}
}
Ok(tt::Subtree { delimiter: template.delimiter, token_trees: buf })
}
fn expand_var(ctx: &mut ExpandCtx, v: &SmolStr) -> Result<Fragment, ExpandError> {
let res = if v == "crate" {
// We simply produce identifier `$crate` here. And it will be resolved when lowering ast to Path.
let tt =
tt::Leaf::from(tt::Ident { text: "$crate".into(), id: tt::TokenId::unspecified() })
.into();
Fragment::Tokens(tt)
} else if !ctx.bindings.contains(v) {
// Note that it is possible to have a `$var` inside a macro which is not bound.
// For example:
// ```
// macro_rules! foo {
// ($a:ident, $b:ident, $c:tt) => {
// macro_rules! bar {
// ($bi:ident) => {
// fn $bi() -> u8 {$c}
// }
// }
// }
// ```
// We just treat it a normal tokens
let tt = tt::Subtree {
delimiter: tt::Delimiter::None,
token_trees: vec![
tt::Leaf::from(tt::Punct { char: '$', spacing: tt::Spacing::Alone }).into(),
tt::Leaf::from(tt::Ident { text: v.clone(), id: tt::TokenId::unspecified() })
.into(),
],
}
.into();
Fragment::Tokens(tt)
} else {
let fragment = ctx.bindings.get(&v, &ctx.nesting)?.clone();
ctx.var_expanded = true;
fragment
};
Ok(res)
}
fn expand_repeat(
ctx: &mut ExpandCtx,
template: &tt::Subtree,
kind: RepeatKind,
separator: Option<Separator>,
) -> Result<Fragment, ExpandError> {
let mut buf: Vec<tt::TokenTree> = Vec::new();
ctx.nesting.push(0);
// Dirty hack to make macro-expansion terminate.
// This should be replaced by a propper macro-by-example implementation
let mut limit = 65536;
let mut has_seps = 0;
let mut counter = 0;
// We store the old var expanded value, and restore it later
// It is because before this `$repeat`,
// it is possible some variables already expanad in the same subtree
//
// `some_var_expanded` keep check if the deeper subtree has expanded variables
let mut some_var_expanded = false;
let old_var_expanded = ctx.var_expanded;
ctx.var_expanded = false;
while let Ok(mut t) = expand_subtree(ctx, template) {
t.delimiter = tt::Delimiter::None;
// if no var expanded in the child, we count it as a fail
if !ctx.var_expanded {
break;
}
// Reset `ctx.var_expandeded` to see if there is other expanded variable
// in the next matching
some_var_expanded = true;
ctx.var_expanded = false;
counter += 1;
limit -= 1;
if limit == 0 {
log::warn!(
"expand_tt excced in repeat pattern exceed limit => {:#?}\n{:#?}",
template,
ctx
);
break;
}
let idx = ctx.nesting.pop().unwrap();
ctx.nesting.push(idx + 1);
push_subtree(&mut buf, t);
if let Some(ref sep) = separator {
match sep {
Separator::Ident(ident) => {
has_seps = 1;
buf.push(tt::Leaf::from(ident.clone()).into());
}
Separator::Literal(lit) => {
has_seps = 1;
buf.push(tt::Leaf::from(lit.clone()).into());
}
Separator::Puncts(puncts) => {
has_seps = puncts.len();
for punct in puncts {
buf.push(tt::Leaf::from(*punct).into());
}
}
}
}
if RepeatKind::ZeroOrOne == kind {
break;
}
}
// Restore the `var_expanded` by combining old one and the new one
ctx.var_expanded = some_var_expanded || old_var_expanded;
ctx.nesting.pop().unwrap();
for _ in 0..has_seps {
buf.pop();
}
if RepeatKind::OneOrMore == kind && counter == 0 {
return Err(ExpandError::UnexpectedToken);
}
// Check if it is a single token subtree without any delimiter
// e.g {Delimiter:None> ['>'] /Delimiter:None>}
let tt = tt::Subtree { delimiter: tt::Delimiter::None, token_trees: buf }.into();
Ok(Fragment::Tokens(tt))
}
fn push_fragment(buf: &mut Vec<tt::TokenTree>, fragment: Fragment) {
match fragment {
Fragment::Tokens(tt::TokenTree::Subtree(tt)) => push_subtree(buf, tt),
Fragment::Tokens(tt) | Fragment::Ast(tt) => buf.push(tt),
}
}
fn push_subtree(buf: &mut Vec<tt::TokenTree>, tt: tt::Subtree) {
match tt.delimiter {
tt::Delimiter::None => buf.extend(tt.token_trees),
_ => buf.push(tt.into()),
}
}
|
