Explain invocation presentation failures

reporter_error_test.go

@@ -1,12 +1,67 @@
 package commandkit
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"io"
+	"strings"
 	"testing"
 )
 
+func TestReporterExplainsItsOwnFailuresWithoutExposingCauses(t *testing.T) {
+	for _, kind := range []string{"output", "diagnostics"} {
+		for _, quiet := range []bool{false, true} {
+			t.Run(fmt.Sprintf("%s/quiet=%t", kind, quiet), func(t *testing.T) {
+				var diagnostics bytes.Buffer
+				reporter := newReporter(Streams{Err: &diagnostics})
+				if quiet {
+					reporter.setVisibility(modeQuiet, false, false)
+				}
+				failure := errors.New("private rendering detail")
+				render := func(io.Writer) error { return failure }
+				if kind == "output" {
+					_ = reporter.RenderOutput(render)
+				} else {
+					_ = reporter.Warn("", render)
+				}
+				cause := errors.New("private application cause")
+				got := reporter.finalize(Domain("example", 0).WithCause(cause), nil)
+				if got.Kind != OutcomeDomain || got.Status != 1 || got.Cause != cause {
+					t.Fatalf("outcome=%#v", got)
+				}
+				if !strings.Contains(got.Explanation.Message, "render") || !strings.Contains(got.Explanation.Message, kind) || !strings.Contains(diagnostics.String(), got.Explanation.Message) {
+					t.Fatalf("explanation=%#v diagnostics=%q", got.Explanation, diagnostics.String())
+				}
+				if strings.Contains(diagnostics.String(), "private") {
+					t.Fatalf("private error text was exposed: %q", diagnostics.String())
+				}
+			})
+		}
+	}
+}
+
+func TestReporterPreservesExplicitSuccessExplanationOnPresentationFailure(t *testing.T) {
+	for _, message := range []string{"supplied context", ""} {
+		t.Run(message, func(t *testing.T) {
+			var diagnostics bytes.Buffer
+			reporter := newReporter(Streams{Err: &diagnostics})
+			_ = reporter.RenderOutput(func(io.Writer) error { return errors.New("render failed") })
+			calls := 0
+			got := reporter.finalize(Success().WithExplanation(message, func(io.Writer) error {
+				calls++
+				return nil
+			}), nil)
+			if got.Status != 1 || got.Explanation.Message != message || calls != 1 {
+				t.Fatalf("outcome=%#v calls=%d", got, calls)
+			}
+			if message == "" && diagnostics.Len() != 0 {
+				t.Fatalf("explicit zero-byte explanation replaced: %q", diagnostics.String())
+			}
+		})
+	}
+}
+
 func TestReporterPreservesJoinedRendererEvidence(t *testing.T) {
 	for _, kind := range []string{"output", "detail"} {
 		for _, test := range []struct {