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Expand unmatched mbe fragments to reasonable default token trees

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Currently we expand unmatched fragments by not replacing them at all,
leaving us with `$ident`. This trips up the parser or subsequent macro
calls. Instead it makes more sense to replace these with some reasonable
default depending on the fragment kind which should make more recursive
macro calls work better for completions.
This commit is contained in:
Lukas Wirth 2022-10-10 14:25:14 +02:00
parent 476d043874
commit 78f33c0e96
6 changed files with 146 additions and 45 deletions
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57
crates/mbe/src/expander/transcriber.rs
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@ -6,7 +6,7 @@ use tt::{Delimiter, Subtree};
use crate::{
expander::{Binding, Bindings, Fragment},
parser::{Op, RepeatKind, Separator},
parser::{MetaVarKind, Op, RepeatKind, Separator},
ExpandError, ExpandResult, MetaTemplate,
};
@ -15,7 +15,7 @@ impl Bindings {
self.inner.contains_key(name)
}
fn get(&self, name: &str, nesting: &mut [NestingState]) -> Result<&Fragment, ExpandError> {
fn get(&self, name: &str, nesting: &mut [NestingState]) -> Result<Fragment, ExpandError> {
macro_rules! binding_err {
($($arg:tt)*) => { ExpandError::binding_error(format!($($arg)*)) };
}
@ -26,6 +26,7 @@ impl Bindings {
nesting_state.hit = true;
b = match b {
Binding::Fragment(_) => break,
Binding::Missing(_) => break,
Binding::Nested(bs) => bs.get(nesting_state.idx).ok_or_else(|| {
nesting_state.at_end = true;
binding_err!("could not find nested binding `{name}`")
@ -37,7 +38,55 @@ impl Bindings {
};
}
match b {
Binding::Fragment(it) => Ok(it),
Binding::Fragment(it) => Ok(it.clone()),
// emit some reasonable default expansion for missing bindings,
// this gives better recovery than emitting the `$fragment-name` verbatim
Binding::Missing(it) => Ok(match it {
MetaVarKind::Stmt => {
Fragment::Tokens(tt::TokenTree::Leaf(tt::Leaf::Punct(tt::Punct {
id: tt::TokenId::unspecified(),
char: ';',
spacing: tt::Spacing::Alone,
})))
}
MetaVarKind::Block => Fragment::Tokens(tt::TokenTree::Subtree(tt::Subtree {
delimiter: Some(tt::Delimiter {
id: tt::TokenId::unspecified(),
kind: tt::DelimiterKind::Brace,
}),
token_trees: vec![],
})),
// FIXME: Meta and Item should get proper defaults
MetaVarKind::Meta | MetaVarKind::Item | MetaVarKind::Tt | MetaVarKind::Vis => {
Fragment::Tokens(tt::TokenTree::Subtree(tt::Subtree {
delimiter: None,
token_trees: vec![],
}))
}
MetaVarKind::Path
| MetaVarKind::Ty
| MetaVarKind::Pat
| MetaVarKind::PatParam
| MetaVarKind::Expr
| MetaVarKind::Ident => {
Fragment::Tokens(tt::TokenTree::Leaf(tt::Leaf::Ident(tt::Ident {
text: SmolStr::new_inline("missing"),
id: tt::TokenId::unspecified(),
})))
}
MetaVarKind::Lifetime => {
Fragment::Tokens(tt::TokenTree::Leaf(tt::Leaf::Ident(tt::Ident {
text: SmolStr::new_inline("'missing"),
id: tt::TokenId::unspecified(),
})))
}
MetaVarKind::Literal => {
Fragment::Tokens(tt::TokenTree::Leaf(tt::Leaf::Ident(tt::Ident {
text: SmolStr::new_inline("\"missing\""),
id: tt::TokenId::unspecified(),
})))
}
}),
Binding::Nested(_) => {
Err(binding_err!("expected simple binding, found nested binding `{name}`"))
}
@ -157,7 +206,7 @@ fn expand_var(ctx: &mut ExpandCtx<'_>, v: &SmolStr, id: tt::TokenId) -> ExpandRe
} else {
ctx.bindings.get(v, &mut ctx.nesting).map_or_else(
|e| ExpandResult { value: Fragment::Tokens(tt::TokenTree::empty()), err: Some(e) },
|b| ExpandResult::ok(b.clone()),
|it| ExpandResult::ok(it),
)
}
}