fix(confusion-matrix): name every missing required flag, in flag order

cmd/internal-tools/confusion-matrix/main.go

@@ -54,16 +54,25 @@ func run(arguments []string, stdout, stderr io.Writer) error {
 	if err := flagSet.Parse(arguments); err != nil {
 		return err
 	}
-	for name, value := range map[string]string{
-		"--sweep":            sweepDirectory,
-		"--reviews":          reviewsDirectory,
-		"--assignment":       assignmentPath,
-		"--property-clauses": mappingPath,
+	// Every missing flag is named together, in flag order: stopping at the
+	// first turns one rerun into one rerun per missing flag.
+	var missing []error
+	for _, required := range []struct {
+		name  string
+		value string
+	}{
+		{"--sweep", sweepDirectory},
+		{"--reviews", reviewsDirectory},
+		{"--assignment", assignmentPath},
+		{"--property-clauses", mappingPath},
 	} {
-		if value == "" {
-			return fmt.Errorf("%s is required", name)
+		if required.value == "" {
+			missing = append(missing, fmt.Errorf("%s is required", required.name))
 		}
 	}
+	if err := errors.Join(missing...); err != nil {
+		return err
+	}
 
 	mapping, err := loadMapping(mappingPath)
 	if err != nil {

cmd/internal-tools/confusion-matrix/parse_test.go

@@ -31,6 +31,31 @@ func scoredFixture(name, model string) fixtureImplementation {
 	}
 }
 
+// Three flags missing is one rerun, not three: the operator is told about all
+// of them at once, in flag order, whatever order the check happened to walk.
+func TestRunNamesEveryMissingRequiredFlagInFlagOrder(t *testing.T) {
+	var stdout, stderr bytes.Buffer
+	err := run([]string{"--sweep", "s"}, &stdout, &stderr)
+	if err == nil {
+		t.Fatal("got no error, want every missing flag named")
+	}
+	message := err.Error()
+	previous := -1
+	for _, name := range []string{"--reviews", "--assignment", "--property-clauses"} {
+		at := strings.Index(message, name)
+		if at < 0 {
+			t.Fatalf("got %q, want %s named", message, name)
+		}
+		if at < previous {
+			t.Errorf("got %q, want the flags named in flag order", message)
+		}
+		previous = at
+	}
+	if strings.Contains(message, "--sweep") {
+		t.Errorf("got %q, want the supplied --sweep left out", message)
+	}
+}
+
 func TestMappingRefusesInputTheMatrixCannotBeScoredFrom(t *testing.T) {
 	tests := []struct {
 		name    string