1 files changed, 42 insertions, 0 deletions
diff --git a/internal/engine/match.go b/internal/engine/match.go
index e68a6e8..ffee7f0 100644
--- a/internal/engine/match.go
+++ b/internal/engine/match.go
@@ -33,6 +33,12 @@ type FileMatch struct {
 	File     scan.File
 	Rules    []RuleMatch // matching rules in order, ending at the first with (stop)
 	Warnings []string    // "<rule>: <warning>", e.g. "acme: content unreadable: needs pdftotext, not installed"
+
+	// NoDelete is non-empty when no delete step may run for this file (spec
+	// §5.5 rule 2), and says why: the file is a duplicate under a scope its
+	// directory's rules use, or that check failed. Only set for a file some
+	// matching rule would delete.
+	NoDelete string
 }
 
 // Result is everything Match found in one directory.
@@ -127,9 +133,45 @@ func evalFile(run *matchRun, file scan.File) FileMatch {
 			break
 		}
 	}
+	if len(run.d.DupScopes) > 0 && deletes(fm.Rules) {
+		fm.NoDelete = noDelete(f, run.d.DupScopes)
+	}
 	return fm
 }
 
+// NeverDeleted is the reason a duplicate's delete step is skipped (spec
+// §5.5).
+const NeverDeleted = "a duplicate is never deleted"
+
+// deletes reports whether any of rules has a delete action.
+func deletes(rules []RuleMatch) bool {
+	for _, rm := range rules {
+		for _, a := range rm.Rule.Conf.Actions {
+			if a.Kind == config.Delete || a.Kind == config.DeletePermanent {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+// noDelete looks f up under every scope, whether or not evaluating the
+// rules reached that test (spec §5.5 rule 2), and returns why f must not be
+// deleted, or "" when it may be. A failed lookup blocks the delete too:
+// krino cannot show the file is not a duplicate, so it keeps it.
+func noDelete(f *facts, scopes [][]string) string {
+	for _, dirs := range scopes {
+		_, dup, err := f.Duplicate(dirs)
+		if err != nil {
+			return "duplicate check failed, so not deleted: " + err.Error()
+		}
+		if dup {
+			return NeverDeleted
+		}
+	}
+	return ""
+}
+
 // RuleTrace is one rule's outcome in an Explain call.
 type RuleTrace struct {
 	Rule    *Rule