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Fix transliterator fallback loading #5468

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Fix transliterator fallback loading #5468

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82 changes: 44 additions & 38 deletions components/experimental/src/transliterate/transliterator/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -306,21 +306,31 @@ impl Transliterator {
// 1. Insert a placeholder to avoid infinite recursion.
env.insert(dep.to_string(), InternalTransliterator::Null);
// 2. Load the transliterator, by checking
let internal_t = dep
// a) hardcoded specials
.strip_prefix("x-")
.map(|special| Transliterator::load_special(special, normalizer_provider))
// b) the user-provided override
.or_else(|| Transliterator::load_with_override(&dep, lookup?).transpose())
// c) the data
.unwrap_or_else(|| {
let mut internal_t = None;
// a) hardcoded specials
if let Some(special) = dep.strip_prefix("x-") {
internal_t = Transliterator::load_special(special, normalizer_provider)?;
}
// b) the user-provided override
if let Some(lookup) = lookup {
if internal_t.is_none() {
if let Ok(locale) = dep.parse() {
internal_t = Transliterator::load_with_override(&locale, lookup)?;
}
}
}
// c) the data
let internal_t = match internal_t {
Some(t) => t,
None => {
let rbt = Transliterator::load_rbt(
#[allow(clippy::unwrap_used)] // infallible
DataMarkerAttributes::try_from_str(&dep.to_ascii_lowercase()).unwrap(),
transliterator_provider,
)?;
Ok(InternalTransliterator::RuleBased(rbt))
})?;
Comment on lines -309 to -323
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I find this much more readable than the mutable Option you're using.

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Problems I had with the previous code:

  1. It was concealing the bug
  2. The functions involved return a mix of Option and Result and it is hard to keep track of which level you are at in unwrapping the values
  3. It's difficult to run the debugger with all the closures. You have to dip in and out of the Rust standard library with all the closures.

But I can convert this back to using the option chain if you prefer, as the code owner.

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The bug is fixed by having load_special return Option<Result<...>>. Here you only need to change the map to an and_then.

InternalTransliterator::RuleBased(rbt)
}
};
if let InternalTransliterator::RuleBased(rbt) = &internal_t {
// 3. Recursively load the dependencies of the dependency.
Self::load_dependencies_recursive(
Expand All @@ -341,7 +351,7 @@ impl Transliterator {
fn load_special<P>(
special: &str,
normalizer_provider: &P,
) -> Result<InternalTransliterator, DataError>
) -> Result<Option<InternalTransliterator>, DataError>
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I think this should be Option<Result<InternalTransliterator, DataError>>. The option signals that a special transliterator is implemented, and then the result is the result from instantiating that transliterator, i.e. the _ case should just be None.

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Either way is fine except that Result<Option> means that I can use the ? operator.

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You don't need the ? opearator:

"any-nfkc" => Some(ComposingTransliterator::try_nfkc(normalizer_provider).map(InternalTransliterator::Composing)),

where
P: DataProvider<CanonicalDecompositionDataV1Marker>
+ DataProvider<CompatibilityDecompositionSupplementV1Marker>
Expand All @@ -352,51 +362,47 @@ impl Transliterator {
{
// TODO(#3909, #3910): add more
match special {
"any-nfc" => Ok(InternalTransliterator::Composing(
"any-nfc" => Ok(Some(InternalTransliterator::Composing(
ComposingTransliterator::try_nfc(normalizer_provider)?,
)),
"any-nfkc" => Ok(InternalTransliterator::Composing(
))),
"any-nfkc" => Ok(Some(InternalTransliterator::Composing(
ComposingTransliterator::try_nfkc(normalizer_provider)?,
)),
"any-nfd" => Ok(InternalTransliterator::Decomposing(
))),
"any-nfd" => Ok(Some(InternalTransliterator::Decomposing(
DecomposingTransliterator::try_nfd(normalizer_provider)?,
)),
"any-nfkd" => Ok(InternalTransliterator::Decomposing(
))),
"any-nfkd" => Ok(Some(InternalTransliterator::Decomposing(
DecomposingTransliterator::try_nfkd(normalizer_provider)?,
)),
"any-null" => Ok(InternalTransliterator::Null),
"any-remove" => Ok(InternalTransliterator::Remove),
"any-hex/unicode" => Ok(InternalTransliterator::Hex(
))),
"any-null" => Ok(Some(InternalTransliterator::Null)),
"any-remove" => Ok(Some(InternalTransliterator::Remove)),
"any-hex/unicode" => Ok(Some(InternalTransliterator::Hex(
hardcoded::HexTransliterator::new("U+", "", 4, Case::Upper),
)),
"any-hex/rust" => Ok(InternalTransliterator::Hex(
))),
"any-hex/rust" => Ok(Some(InternalTransliterator::Hex(
hardcoded::HexTransliterator::new("\\u{", "}", 2, Case::Lower),
)),
"any-hex/xml" => Ok(InternalTransliterator::Hex(
))),
"any-hex/xml" => Ok(Some(InternalTransliterator::Hex(
hardcoded::HexTransliterator::new("&#x", ";", 1, Case::Upper),
)),
"any-hex/perl" => Ok(InternalTransliterator::Hex(
))),
"any-hex/perl" => Ok(Some(InternalTransliterator::Hex(
hardcoded::HexTransliterator::new("\\x{", "}", 1, Case::Upper),
)),
"any-hex/plain" => Ok(InternalTransliterator::Hex(
))),
"any-hex/plain" => Ok(Some(InternalTransliterator::Hex(
hardcoded::HexTransliterator::new("", "", 4, Case::Upper),
)),
s => Err(DataError::custom("unavailable transliterator").with_debug_context(s)),
))),
_ => Ok(None),
}
}

fn load_with_override<F>(
id: &str,
locale: &Locale,
lookup: &F,
) -> Result<Option<InternalTransliterator>, DataError>
where
F: Fn(&Locale) -> Option<Box<dyn CustomTransliterator>>,
{
let locale: Locale = id.parse().map_err(|e| {
DataError::custom("invalid data: transliterator dependency is not a valid Locale")
.with_debug_context(&e)
})?;
Ok(lookup(&locale).map(InternalTransliterator::Dyn))
Ok(lookup(locale).map(InternalTransliterator::Dyn))
}

fn load_rbt<P>(
Expand Down