[rustc_span][perf] Remove unnecessary string joins and allocs.

ttsugriy · ttsugriy · commit f74eee2fa662 · 2023-08-01T16:57:43.000-07:00
Comparing vectors of string parts yields the same result but avoids
unnecessary `join` and potential allocation for resulting `String`.
This code is cold so it's unlikely to have any measurable impact, but
considering but since it's also simpler, why not? :)
diff --git a/compiler/rustc_span/src/edit_distance.rs b/compiler/rustc_span/src/edit_distance.rs
@@ -247,9 +247,9 @@ fn find_match_by_sorted_words(iter_names: &[Symbol], lookup: &str) -> Option<Sym
     })
 }
 
-fn sort_by_words(name: &str) -> String {
+fn sort_by_words(name: &str) -> Vec<&str> {
     let mut split_words: Vec<&str> = name.split('_').collect();
     // We are sorting primitive &strs and can use unstable sort here.
     split_words.sort_unstable();
-    split_words.join("_")
+    split_words
 }

Original file line number	Diff line number	Diff line change
`@@ -247,9 +247,9 @@ fn find_match_by_sorted_words(iter_names: &[Symbol], lookup: &str) -> Option<Sym`
`247`	`247`	`})`
`248`	`248`	`}`
`249`	`249`
`250`		`-fn sort_by_words(name: &str) -> String {`
	`250`	`+fn sort_by_words(name: &str) -> Vec<&str> {`
`251`	`251`	`let mut split_words: Vec<&str> = name.split('_').collect();`
`252`	`252`	`// We are sorting primitive &strs and can use unstable sort here.`
`253`	`253`	`split_words.sort_unstable();`
`254`		`- split_words.join("_")`
	`254`	`+ split_words`
`255`	`255`	`}`