perf(dict): Bypass vars when possible

Variant support slows us down by 10-50$.  I assume most people will run
with `en` and so most of this overhead is to waste.  So instead of
merging vars with dict, let's instead get a quick win by just skipping
vars when we don't need to.  If the assumptions behind this change over
time or if there is need for speeding up a specific locale, we can
re-address this.

Before:
```
check_file/Typos/code   time:   [35.860 us 36.021 us 36.187 us]
                        thrpt:  [8.0117 MiB/s 8.0486 MiB/s 8.0846 MiB/s]
check_file/Typos/corpus time:   [26.966 ms 27.215 ms 27.521 ms]
                        thrpt:  [21.127 MiB/s 21.365 MiB/s 21.562 MiB/s]
```
After:
```
check_file/Typos/code   time:   [33.837 us 33.928 us 34.031 us]
                        thrpt:  [8.5191 MiB/s 8.5452 MiB/s 8.5680 MiB/s]
check_file/Typos/corpus time:   [17.521 ms 17.620 ms 17.730 ms]
                        thrpt:  [32.794 MiB/s 32.999 MiB/s 33.184 MiB/s]
```

This puts us inline with `--no-default-features --features dict`

Fixes #253

crates/typos-vars/codegen/src/main.rs

@@ -78,6 +78,7 @@ fn generate_variations<W: std::io::Write>(file: &mut W) {
 
     let mut smallest = usize::MAX;
     let mut largest = usize::MIN;
+    let mut no_invalid = true;
 
     writeln!(
         file,
@@ -97,6 +98,8 @@ fn generate_variations<W: std::io::Write>(file: &mut W) {
         builder.entry(unicase::UniCase::new(word), &value);
         smallest = std::cmp::min(smallest, word.len());
         largest = std::cmp::max(largest, word.len());
+
+        no_invalid &= !is_always_invalid(data);
     }
     let codegenned = builder.build();
     writeln!(file, "{}", codegenned).unwrap();
@@ -110,6 +113,10 @@ fn generate_variations<W: std::io::Write>(file: &mut W) {
     )
     .unwrap();
 
+    writeln!(file).unwrap();
+    writeln!(file, "pub const NO_INVALID: bool = {:?};", no_invalid,).unwrap();
+
+    writeln!(file).unwrap();
     for (symbol, entry) in entries.iter() {
         if !referenced_symbols.contains(symbol.as_str()) {
             continue;
@@ -156,6 +163,15 @@ fn is_always_valid(data: &[(&str, varcon::CategorySet)]) -> bool {
     false
 }
 
+fn is_always_invalid(data: &[(&str, varcon::CategorySet)]) -> bool {
+    for (_symbol, set) in data.iter() {
+        if set.is_empty() {
+            return true;
+        }
+    }
+    false
+}
+
 fn entries() -> BTreeMap<String, varcon_core::Entry> {
     varcon::VARCON
         .iter()

crates/typos-vars/src/vars_codegen.rs

@@ -113083,6 +113083,9 @@ pub static VARS_DICTIONARY: phf::Map<
 };
 
 pub const WORD_RANGE: std::ops::RangeInclusive<usize> = 2..=24;
+
+pub const NO_INVALID: bool = true;
+
 pub(crate) static ENTRY_ABETTORS_7043394254318611656: VariantsMap =
     [&["abettors"], &["abetters"], &["abettors"], &["abetters"]];
 

src/dict.rs

@@ -72,33 +72,42 @@ impl BuiltIn {
 #[cfg(feature = "vars")]
 impl BuiltIn {
     fn chain_with_vars(&self, corrections: &'static [&'static str]) -> Status<'static> {
-        let mut chained: Vec<_> = corrections
-            .iter()
-            .flat_map(|c| match self.correct_with_vars(c) {
-                Some(Status::Valid) | None => vec![Cow::Borrowed(*c)],
-                Some(Status::Corrections(vars)) => vars,
-                Some(Status::Invalid) => {
-                    unreachable!("correct_with_vars should always have valid suggestions")
-                }
-            })
-            .collect();
-        if chained.len() != 1 {
-            chained.sort_unstable();
-            chained.dedup();
+        if self.is_vars_enabled() {
+            let mut chained: Vec<_> = corrections
+                .iter()
+                .flat_map(|c| match self.correct_with_vars(c) {
+                    Some(Status::Valid) | None => vec![Cow::Borrowed(*c)],
+                    Some(Status::Corrections(vars)) => vars,
+                    Some(Status::Invalid) => {
+                        unreachable!("correct_with_vars should always have valid suggestions")
+                    }
+                })
+                .collect();
+            if chained.len() != 1 {
+                chained.sort_unstable();
+                chained.dedup();
+            }
+            debug_assert!(!chained.is_empty());
+            Status::Corrections(chained)
+        } else {
+            Status::Corrections(corrections.iter().map(|c| Cow::Borrowed(*c)).collect())
         }
-        debug_assert!(!chained.is_empty());
-        Status::Corrections(chained)
     }
 
     fn correct_with_vars(&self, word: &str) -> Option<Status<'static>> {
-        if typos_vars::WORD_RANGE.contains(&word.len()) {
+        if self.is_vars_enabled() && typos_vars::WORD_RANGE.contains(&word.len()) {
             map_lookup(&typos_vars::VARS_DICTIONARY, word)
                 .map(|variants| self.select_variant(variants))
         } else {
             None
         }
     }
 
+    fn is_vars_enabled(&self) -> bool {
+        debug_assert!(typos_vars::NO_INVALID);
+        self.locale.is_some()
+    }
+
     fn select_variant(
         &self,
         vars: &'static [(u8, &'static typos_vars::VariantsMap)],