similar_names stop linting for 3-char names (rust-lang#15100)

fixes rust-lang#14869

Added a simple check if both chars are of length 3
If they are, we skip the check for that pair.

This won't handle the 4 v 3 case.
Not sure if this was the intent of the issue.

Also saw we have some hardcoded exemptions for `set, get` and `lhs, rhs`
Tried removing them thinking they would be handled by the new condition.
But we have to keep because they allow for `bla_lhs` v `bla_rhs` to be
skipped

changelog:[`similar_names`]: Stop triggering for 3-character names

Author: blyxyas

clippy_lints/src/non_expressive_names.rs

@@ -248,6 +248,11 @@ impl SimilarNamesNameVisitor<'_, '_, '_> {
                 continue;
             }
 
+            // Skip similarity check if both names are exactly 3 characters
+            if count == 3 && existing_name.len == 3 {
+                continue;
+            }
+
             let dissimilar = match existing_name.len.cmp(&count) {
                 Ordering::Greater => existing_name.len - count != 1 || levenstein_not_1(interned_name, existing_str),
                 Ordering::Less => count - existing_name.len != 1 || levenstein_not_1(existing_str, interned_name),

clippy_utils/src/ast_utils/mod.rs

@@ -325,7 +325,7 @@ pub fn eq_item<K>(l: &Item<K>, r: &Item<K>, mut eq_kind: impl FnMut(&K, &K) -> b
     over(&l.attrs, &r.attrs, eq_attr) && eq_vis(&l.vis, &r.vis) && eq_kind(&l.kind, &r.kind)
 }
 
-#[expect(clippy::similar_names, clippy::too_many_lines)] // Just a big match statement
+#[expect(clippy::too_many_lines)] // Just a big match statement
 pub fn eq_item_kind(l: &ItemKind, r: &ItemKind) -> bool {
     use ItemKind::*;
     match (l, r) {

tests/ui/similar_names.rs

@@ -89,6 +89,10 @@ fn main() {
 
     let iter: i32;
     let item: i32;
+
+    // 3 letter names are allowed to be similar
+    let kta: i32;
+    let ktv: i32;
 }
 
 fn foo() {

tests/ui/similar_names.stderr

@@ -49,13 +49,13 @@ LL |     let parser: i32;
    |         ^^^^^^
 
 error: binding's name is too similar to existing binding
-  --> tests/ui/similar_names.rs:98:16
+  --> tests/ui/similar_names.rs:102:16
    |
 LL |         bpple: sprang,
    |                ^^^^^^
    |
 note: existing binding defined here
-  --> tests/ui/similar_names.rs:97:16
+  --> tests/ui/similar_names.rs:101:16
    |
 LL |         apple: spring,
    |                ^^^^^^