gopls/internal: fix extract refactor for cases with anonymous functions

This fix ignores return statements inside anonymous functions. These
return statements can be ignored because they does not meddle with
the control flow of the outer function.

Fixes golang/go#64821

Change-Id: I21f82f8663bf3343412d5b537802a56efc34495f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/617335
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Robert Findley <rfindley@google.com>

gopls/internal/golang/extract.go

@@ -246,6 +246,10 @@ func extractFunctionMethod(fset *token.FileSet, start, end token.Pos, src []byte
 		if n.Pos() < start || n.End() > end {
 			return n.Pos() <= end
 		}
+		// exclude return statements in function literals because they don't affect the refactor.
+		if _, ok := n.(*ast.FuncLit); ok {
+			return false
+		}
 		ret, ok := n.(*ast.ReturnStmt)
 		if !ok {
 			return true

gopls/internal/test/marker/testdata/codeaction/functionextraction.txt

@@ -581,3 +581,36 @@ func newFunction() (int, error) {
 	return u, err
 }
 
+-- anonymousfunc.go --
+package extract
+import "cmp"
+import "slices"
+
+// issue go#64821
+func _() {
+	var s []string //@codeaction("var", anonEnd, "refactor.extract.function", anon1)
+	slices.SortFunc(s, func(a, b string) int {
+		return cmp.Compare(a, b)
+	})
+	println(s) //@loc(anonEnd, ")")
+}
+
+-- @anon1/anonymousfunc.go --
+package extract
+import "cmp"
+import "slices"
+
+// issue go#64821
+func _() {
+	//@codeaction("var", anonEnd, "refactor.extract.function", anon1)
+	newFunction() //@loc(anonEnd, ")")
+}
+
+func newFunction() {
+	var s []string
+	slices.SortFunc(s, func(a, b string) int {
+		return cmp.Compare(a, b)
+	})
+	println(s)
+}
+