progress: tweak progress error reporting

This commit adds catpure of os.Std{out,err} when running osbuild so
that we capture the error log and can display it as part of
an error from osbuild, e.g. when osbuild itself crashes.

This gives us more accurate error reporting if anything fails
during the osbuild building.

bib/pkg/progress/export_test.go

@@ -25,3 +25,11 @@ func MockIsattyIsTerminal(fn func(uintptr) bool) (restore func()) {
 		isattyIsTerminal = saved
 	}
 }
+
+func MockOsbuildCmd(s string) (restore func()) {
+	saved := osbuildCmd
+	osbuildCmd = s
+	return func() {
+		osbuildCmd = saved
+	}
+}

bib/pkg/progress/progress.go

@@ -333,6 +333,8 @@ func runOSBuildNoProgress(pb ProgressBar, manifest []byte, store, outputDirector
 	return err
 }
 
+var osbuildCmd = "osbuild"
+
 func runOSBuildWithProgress(pb ProgressBar, manifest []byte, store, outputDirectory string, exports, extraEnv []string) error {
 	rp, wp, err := os.Pipe()
 	if err != nil {
@@ -342,7 +344,7 @@ func runOSBuildWithProgress(pb ProgressBar, manifest []byte, store, outputDirect
 	defer wp.Close()
 
 	cmd := exec.Command(
-		"osbuild",
+		osbuildCmd,
 		"--store", store,
 		"--output-directory", outputDirectory,
 		"--monitor=JSONSeqMonitor",
@@ -353,12 +355,11 @@ func runOSBuildWithProgress(pb ProgressBar, manifest []byte, store, outputDirect
 		cmd.Args = append(cmd.Args, "--export", export)
 	}
 
+	var stdio bytes.Buffer
 	cmd.Env = append(os.Environ(), extraEnv...)
 	cmd.Stdin = bytes.NewBuffer(manifest)
-	cmd.Stderr = os.Stderr
-	// we could use "--json" here and would get the build-result
-	// exported here
-	cmd.Stdout = nil
+	cmd.Stdout = &stdio
+	cmd.Stderr = &stdio
 	cmd.ExtraFiles = []*os.File{wp}
 
 	osbuildStatus := osbuild.NewStatusScanner(rp)
@@ -397,7 +398,7 @@ func runOSBuildWithProgress(pb ProgressBar, manifest []byte, store, outputDirect
 	}
 
 	if err := cmd.Wait(); err != nil {
-		return fmt.Errorf("error running osbuild: %w\nLog:\n%s", err, strings.Join(tracesMsgs, "\n"))
+		return fmt.Errorf("error running osbuild: %w\nOutput:\n%s", err, stdio.String())
 	}
 
 	return nil

bib/pkg/progress/progress_test.go

@@ -3,6 +3,8 @@ package progress_test
 import (
 	"bytes"
 	"fmt"
+	"os"
+	"path/filepath"
 	"reflect"
 	"testing"
 
@@ -130,3 +132,27 @@ func TestProgressNewAutoselect(t *testing.T) {
 		assert.Equal(t, reflect.TypeOf(pb), reflect.TypeOf(tc.expected), fmt.Sprintf("[%v] %T not the expected %T", tc.onTerm, pb, tc.expected))
 	}
 }
+
+func makeFakeOsbuild(t *testing.T, content string) string {
+	p := filepath.Join(t.TempDir(), "fake-osbuild")
+	err := os.WriteFile(p, []byte("#!/bin/sh\n"+content), 0755)
+	assert.NoError(t, err)
+	return p
+}
+
+func TestRunOSBuildWithProgress(t *testing.T) {
+	restore := progress.MockOsbuildCmd(makeFakeOsbuild(t, `echo osbuild-stdout-output
+>&2 echo osbuild-stderr-output
+exit 112
+`))
+	defer restore()
+
+	pbar, err := progress.New("debug")
+	assert.NoError(t, err)
+	err = progress.RunOSBuild(pbar, []byte(`{"fake":"manifest"}`), "", "", nil, nil)
+	assert.EqualError(t, err, `error running osbuild: exit status 112
+Output:
+osbuild-stdout-output
+osbuild-stderr-output
+`)
+}