Retain entered flag spellings in parser failures

route_test.go

@@ -11,6 +11,46 @@ import (
 	"testing"
 )
 
+func TestParserFailuresRetainAliasUsageAndFlagSpellings(t *testing.T) {
+	built := 0
+	command := NewCommand(CommandSpec[struct{}]{
+		Name:     "inspect",
+		NewInput: func() struct{} { built++; return struct{}{} },
+		Flags: []Flag[struct{}]{ValueFlag(FlagMeta{Name: "format"}, (*string)(nil),
+			func(value string) (string, error) { return value, nil },
+			func(*struct{}, Supplied[string]) {})},
+		Run: func(Invocation, struct{}) Outcome { t.Fatal("invalid input executed"); return Success() },
+	})
+	app, err := New(Identity{Name: "Demo"}, command, Alias("i", "inspect"),
+		FlagAliasFor("inspect", "--fmt", "--format"),
+		FlagAliasFor("inspect", "-F", "--format"), FlagAlias("--hlep", "--help"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, test := range []struct {
+		args     []string
+		spelling string
+	}{
+		{[]string{"i", "--fmt"}, ": --fmt"},
+		{[]string{"i", "-F"}, ": -F"},
+		{[]string{"i", "--hlep=bad", "--help=true"}, "for --hlep"},
+		{[]string{"i", "-h=bad"}, "for -h"},
+	} {
+		t.Run(strings.Join(test.args, " "), func(t *testing.T) {
+			var diagnostics bytes.Buffer
+			outcome := app.Execute(context.Background(), test.args, Streams{Out: io.Discard, Err: &diagnostics})
+			if outcome.Kind != OutcomeUsage || built != 0 {
+				t.Fatalf("outcome = %#v, inputs built = %d", outcome, built)
+			}
+			for _, fragment := range []string{test.spelling, "Usage: Demo i", "Alias for: Demo inspect"} {
+				if !strings.Contains(diagnostics.String(), fragment) {
+					t.Errorf("diagnostics %q omit %q", diagnostics.String(), fragment)
+				}
+			}
+		})
+	}
+}
+
 func TestCommandContextSurvivesIncompleteAndInvalidOperandCounts(t *testing.T) {
 	for _, spelling := range []string{"run", "r"} {
 		for _, test := range []struct {