go/types, types2: use ":" as start of implicit type switch case scopes

Adjust the respective API test accordingly.

Change-Id: I7ecc8899b40ae3b5aeb2c1e032935c672b41e0b6
Reviewed-on: https://go-review.googlesource.com/c/go/+/592675
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/compile/internal/types2/api_test.go

@@ -1884,6 +1884,9 @@ func TestScopeLookupParent(t *testing.T) {
 	// Each /*name=kind:line*/ comment makes the test look up the
 	// name at that point and checks that it resolves to a decl of
 	// the specified kind and line number.  "undef" means undefined.
+	// Note that type switch case clauses with an empty body (but for
+	// comments) need the ";" to ensure that the recorded scope extends
+	// past the comments.
 	mainSrc := `
 /*lib=pkgname:5*/ /*X=var:1*/ /*Pi=const:8*/ /*T=typename:9*/ /*Y=var:10*/ /*F=func:12*/
 package main
@@ -1907,17 +1910,17 @@ func F[T *U, U any](param1, param2 int) /*param1=undef*/ (res1 /*res1=undef*/, r
 
 	var i interface{}
 	switch y := i.(type) { /*y=undef*/
-	case /*y=undef*/ int /*y=var:23*/ :
+	case /*y=undef*/ int /*y=undef*/ : /*y=var:23*/ ;
-	case float32, /*y=undef*/ float64 /*y=var:23*/ :
+	case float32, /*y=undef*/ float64 /*y=undef*/ : /*y=var:23*/ ;
-	default /*y=var:23*/:
+	default /*y=undef*/ : /*y=var:23*/
 		println(y)
 	}
 	/*y=undef*/
 
         switch int := i.(type) {
-        case /*int=typename:0*/ int /*int=var:31*/ :
+        case /*int=typename:0*/ int /*int=typename:0*/ : /*int=var:31*/
         	println(int)
-        default /*int=var:31*/ :
+        default /*int=typename:0*/ : /*int=var:31*/ ;
         }
 
 	_ = param1

src/cmd/compile/internal/types2/stmt.go

@@ -818,13 +818,7 @@ func (check *Checker) typeSwitchStmt(inner stmtContext, s *syntax.SwitchStmt, gu
 		// If lhs exists, declare a corresponding variable in the case-local scope.
 		if lhs != nil {
 			obj := NewVar(lhs.Pos(), check.pkg, lhs.Value, T)
-			// TODO(mdempsky): Just use clause.Colon? Why did I even suggest
+			check.declare(check.scope, nil, obj, clause.Colon)
-			// "at the end of the TypeSwitchCase" in go.dev/issue/16794 instead?
-			scopePos := clause.Pos() // for default clause (len(List) == 0)
-			if n := len(cases); n > 0 {
-				scopePos = syntax.EndPos(cases[n-1])
-			}
-			check.declare(check.scope, nil, obj, scopePos)
 			check.recordImplicit(clause, obj)
 			// For the "declared and not used" error, all lhs variables act as
 			// one; i.e., if any one of them is 'used', all of them are 'used'.

src/go/types/api_test.go

@@ -1885,6 +1885,9 @@ func TestScopeLookupParent(t *testing.T) {
 	// Each /*name=kind:line*/ comment makes the test look up the
 	// name at that point and checks that it resolves to a decl of
 	// the specified kind and line number.  "undef" means undefined.
+	// Note that type switch case clauses with an empty body (but for
+	// comments) need the ";" to ensure that the recorded scope extends
+	// past the comments.
 	mainSrc := `
 /*lib=pkgname:5*/ /*X=var:1*/ /*Pi=const:8*/ /*T=typename:9*/ /*Y=var:10*/ /*F=func:12*/
 package main
@@ -1908,17 +1911,17 @@ func F[T *U, U any](param1, param2 int) /*param1=undef*/ (res1 /*res1=undef*/, r
 
 	var i interface{}
 	switch y := i.(type) { /*y=undef*/
-	case /*y=undef*/ int /*y=var:23*/ :
+	case /*y=undef*/ int /*y=undef*/ : /*y=var:23*/ ;
-	case float32, /*y=undef*/ float64 /*y=var:23*/ :
+	case float32, /*y=undef*/ float64 /*y=undef*/ : /*y=var:23*/ ;
-	default /*y=var:23*/:
+	default /*y=undef*/ : /*y=var:23*/
 		println(y)
 	}
 	/*y=undef*/
 
         switch int := i.(type) {
-        case /*int=typename:0*/ int /*int=var:31*/ :
+        case /*int=typename:0*/ int /*int=typename:0*/ : /*int=var:31*/
         	println(int)
-        default /*int=var:31*/ :
+        default /*int=typename:0*/ : /*int=var:31*/ ;
         }
 
 	_ = param1

src/go/types/stmt.go

@@ -763,13 +763,7 @@ func (check *Checker) stmt(ctxt stmtContext, s ast.Stmt) {
 			// If lhs exists, declare a corresponding variable in the case-local scope.
 			if lhs != nil {
 				obj := NewVar(lhs.Pos(), check.pkg, lhs.Name, T)
-				// TODO(mdempsky): Just use clause.Colon? Why did I even suggest
+				check.declare(check.scope, nil, obj, clause.Colon)
-				// "at the end of the TypeSwitchCase" in go.dev/issue/16794 instead?
-				scopePos := clause.Pos() + token.Pos(len("default")) // for default clause (len(List) == 0)
-				if n := len(clause.List); n > 0 {
-					scopePos = clause.List[n-1].End()
-				}
-				check.declare(check.scope, nil, obj, scopePos)
 				check.recordImplicit(clause, obj)
 				// For the "declared and not used" error, all lhs variables act as
 				// one; i.e., if any one of them is 'used', all of them are 'used'.