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Optimize import substitution with zero-allocation ImportPathIter #100

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Optimize import substitution with zero-allocation ImportPathIter #100

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47 changes: 33 additions & 14 deletions src/compose/parse_imports.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,22 @@ use super::{
Composer, ImportDefWithOffset, ImportDefinition,
};

enum ImportPathIter<'a> {
Multiple(std::slice::Iter<'a, String>),
Single(std::iter::Once<&'a str>),
}

impl<'a> Iterator for ImportPathIter<'a> {
type Item = &'a str;

fn next(&mut self) -> Option<Self::Item> {
match self {
ImportPathIter::Multiple(iter) => iter.next().map(String::as_str),
ImportPathIter::Single(iter) => iter.next(),
}
}
}

pub fn parse_imports<'a>(
input: &'a str,
declared_imports: &mut IndexMap<String, Vec<String>>,
Expand Down Expand Up @@ -129,20 +145,23 @@ pub fn substitute_identifiers(
Token::Identifier(ident, token_pos) => {
if in_substitution_position {
let (first, residual) = ident.split_once("::").unwrap_or((ident, ""));
let full_paths = declared_imports
.get(first)
.cloned()
.unwrap_or(vec![first.to_owned()]);

if !allow_ambiguous && full_paths.len() > 1 {
return Err(offset + token_pos);
}
let full_paths = match declared_imports.get(first) {
Some(paths) => {
if !allow_ambiguous && paths.len() > 1 {
return Err(offset + token_pos);
}

for mut full_path in full_paths {
if !residual.is_empty() {
full_path.push_str("::");
full_path.push_str(residual);
ImportPathIter::Multiple(paths.iter())
}
None => ImportPathIter::Single(std::iter::once(first)),
};

for path in full_paths {
let full_path = if !residual.is_empty() {
&format!("{}::{}", path, residual)
} else {
path
};

if let Some((module, item)) = full_path.rsplit_once("::") {
used_imports
Expand All @@ -159,7 +178,7 @@ pub fn substitute_identifiers(
.push(item.to_owned());
output.push_str(item);
output.push_str(&Composer::decorate(module));
} else if full_path.find('"').is_some() {
} else if full_path.contains('"') {
// we don't want to replace local variables that shadow quoted module imports with the
// quoted name as that won't compile.
// since quoted items always refer to modules, we can just emit the original ident
Expand All @@ -169,7 +188,7 @@ pub fn substitute_identifiers(
// if there are no quotes we do the replacement. this means that individually imported
// items can be used, and any shadowing local variables get harmlessly renamed.
// TODO: it can lead to weird errors, but such is life
output.push_str(&full_path);
output.push_str(full_path);
}
}
} else {
Expand Down
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