pkg/prog: Bump deprecation level to 20.

Also add support for setting deprecation level in transcript tests.

pkg/eval/builtin_fn_str_test.elvts

@@ -102,6 +102,8 @@ Exception: port does not support value output
 # eawk #
 ////////
 
+//with-deprecation-level 19
+
 ~> echo "  ax  by cz  \n11\t22 33" | eawk {|@a| put $a[-1] }
 ▶ cz
 ▶ 33

pkg/eval/evaltest/test_transcript.go

@@ -8,6 +8,7 @@ import (
 	"io/fs"
 	"regexp"
 	"runtime"
+	"strconv"
 	"strings"
 	"testing"
 
@@ -18,6 +19,7 @@ import (
 	"src.elv.sh/pkg/mods"
 	"src.elv.sh/pkg/must"
 	"src.elv.sh/pkg/parse"
+	"src.elv.sh/pkg/prog"
 	"src.elv.sh/pkg/testutil"
 	"src.elv.sh/pkg/transcript"
 )
@@ -68,6 +70,8 @@ import (
 //     and GOOS values and "unix" are recognized as tags; other tags are always
 //     false.
 //
+//   - deprecation-level $x: Run with deprecation level set to $x.
+//
 // Since directives in a higher level propagated to all its descendants, this
 // mechanism can be used to specify setup functions that apply to an entire
 // .elvts file (or an entire elvish-transcript code block in a .elv file) or an
@@ -162,6 +166,9 @@ func buildSetupMaps(setupPairs []any) (map[string]func(*testing.T, *eval.Evaler)
 				t.Skipf("constraint not satisfied: %s", arg)
 			}
 		},
+		"deprecation-level": func(t *testing.T, _ *eval.Evaler, arg string) {
+			testutil.Set(t, &prog.DeprecationLevel, must.OK1(strconv.Atoi(arg)))
+		},
 	}
 	for i := 0; i < len(setupPairs); i += 2 {
 		name := setupPairs[i].(string)

pkg/prog/prog.go

@@ -18,7 +18,7 @@ import (
 // DeprecationLevel is a global flag that controls which deprecations to show.
 // If its value is X, Elvish shows deprecations that should be shown for version
 // 0.X.
-var DeprecationLevel = 19
+var DeprecationLevel = 20
 
 // Program represents a subprogram.
 type Program interface {