meta: fail execution if Fatalf was used

`Fatalf` was storing an error but we were never checking it. It will
now fail the execution.

metamorphic/history.go

@@ -125,7 +125,8 @@ func (h *history) Fatalf(format string, args ...interface{}) {
 		panic(fmt.Sprintf(format, args...))
 	}
 	_ = h.log.Output(2, h.format("FATAL", format, args...))
-	h.err.Store(errors.Errorf(format, args...))
+	// Store the first fatal error message.
+	h.err.CompareAndSwap(nil, errors.Errorf(format, args...))
 }
 
 func (h *history) recorder(
@@ -206,7 +207,11 @@ func reorderHistory(lines []string) []string {
 		if cleaned := strings.TrimSpace(l); cleaned == "" {
 			continue
 		}
-		reordered[extractOp(l)] = l
+		idx := extractOp(l)
+		if idx >= len(reordered) {
+			panic("incomplete test history; this shouldn't happen given that execution completed successfully")
+		}
+		reordered[idx] = l
 	}
 	return reordered
 }

metamorphic/meta.go

@@ -22,12 +22,12 @@ import (
 	"testing"
 	"time"
 
+	"github.com/cockroachdb/errors"
 	"github.com/cockroachdb/pebble/internal/base"
 	"github.com/cockroachdb/pebble/internal/dsl"
 	"github.com/cockroachdb/pebble/internal/randvar"
 	"github.com/cockroachdb/pebble/vfs"
 	"github.com/cockroachdb/pebble/vfs/errorfs"
-	"github.com/pkg/errors"
 	"github.com/pmezard/go-difflib/difflib"
 	"github.com/stretchr/testify/require"
 	"golang.org/x/exp/rand"
@@ -572,6 +572,8 @@ func RunOnce(t TestingT, runDir string, seed uint64, historyPath string, rOpts .
 			fmt.Fprintf(os.Stderr, "\n%s\n", db.LSMViewURL())
 		}
 	}
+	// Don't let the test pass if it issued a Fatalf.
+	err = errors.CombineErrors(err, h.Error())
 
 	if err != nil {
 		m.saveInMemoryData()