Address review

Author: liufengyun

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1009,15 +1009,18 @@ object desugar {
    *             IrrefutableGenFrom:  sel with attachment `CheckIrrefutable -> checkMode`
    */
   def makeSelector(sel: Tree, checkMode: MatchCheck)(using Context): Tree =
-    if (checkMode == MatchCheck.Exhaustive) sel
-    else {
-      if (checkMode == MatchCheck.None)
-        Annotated(sel, New(ref(defn.UncheckedAnnot.typeRef)))
-      else
-        // TODO: use `pushAttachment` and investigate duplicate attachment
-        sel.withAttachment(CheckIrrefutable, checkMode)
-        sel
-    }
+    checkMode match
+    case MatchCheck.None =>
+      Annotated(sel, New(ref(defn.UncheckedAnnot.typeRef)))
+
+    case MatchCheck.Exhaustive =>
+      sel
+
+    case MatchCheck.IrrefutablePatDef | MatchCheck.IrrefutableGenFrom =>
+      // TODO: use `pushAttachment` and investigate duplicate attachment
+      sel.withAttachment(CheckIrrefutable, checkMode)
+      sel
+    end match
 
   /** If `pat` is a variable pattern,
    *

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -671,7 +671,7 @@ trait Checking {
       report.error(ex"$cls cannot be instantiated since it${rstatus.msg}", pos)
   }
 
-  /** Check that pattern `pat` is irrefutable for scrutinee tye `sel.tpe`.
+  /** Check that pattern `pat` is irrefutable for scrutinee type `sel.tpe`.
    *  This means `sel` is either marked @unchecked or `sel.tpe` conforms to the
    *  pattern's type. If pattern is an UnApply, do the check recursively.
    */

docs/docs/reference/changed-features/pattern-bindings.md

@@ -25,7 +25,7 @@ want to decompose it like this:
 ```scala
 val first :: rest = elems   // error
 ```
-This works in Scala 2. In fact it is a typical use case for Scala 2's rules. But in Scala 3.1 it will give a type error. One can avoid the error by marking the rhs with an `@unchecked` annotation:
+This works in Scala 2. In fact it is a typical use case for Scala 2's rules. But in Scala 3.1 it will give a type error. One can avoid the error by marking the right-hand side with an `@unchecked` annotation:
 ```scala
 val first :: rest = elems: @unchecked   // OK
 ```