a rule's duplicate check failure shortens the path too

3 files changed, 77 insertions, 10 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c34962c..af4124c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -43,8 +43,9 @@
   name's continuation lines - in the plan, and in the per-file headings of
   review and undo - start past the label column, so a name cannot pass for
   a step line.
-- Duplicate warnings share one form, `duplicate: PATH: cause`, with the
-  path shortened to `~` and not repeated inside the cause.
+- Duplicate warnings, for the directory and on a rule, name the path
+  shortened to `~` and do not repeat it inside the cause
+  (`duplicate: ~/dl/a.txt: open: permission denied`).
 - `--json` says which exclude set a file aside, carries the warnings raised
   while matching, and lists unmatched files that raised one.
 - A literal `{{` or `}}` in a destination is text, not a placeholder: the
diff --git a/internal/engine/facts.go b/internal/engine/facts.go
index 89bd71b..641f1ef 100644
--- a/internal/engine/facts.go
+++ b/internal/engine/facts.go
@@ -5,6 +5,7 @@ package engine
 import (
 	"context"
 	"errors"
+	"fmt"
 	"io/fs"
 	"path/filepath"
 	"sort"
@@ -83,18 +84,39 @@ func (run *matchRun) drainDupErrors() {
 // PATH: cause", the path abbreviated like every other one shown, and an OS
 // error's cause without the raw path it would repeat.
 func dupWarning(err error) string {
+	return "duplicate: " + dupCause(err).Error()
+}
+
+// dupCause is a duplicate check's error as "PATH: cause", the path
+// shortened with xdg.Abbrev and not repeated inside the cause - a candidate
+// that could not be hashed, or an OS error on the file itself (plan 11
+// review L7). It still unwraps to err.
+func dupCause(err error) error {
+	path, cause := "", err
 	var ce dup.CandidateError
-	if !errors.As(err, &ce) {
-		return "duplicate: " + err.Error()
-	}
-	cause := ce.Err.Error()
 	var pe *fs.PathError
-	if errors.As(ce.Err, &pe) {
-		cause = pe.Op + ": " + pe.Err.Error()
+	switch {
+	case errors.As(err, &ce):
+		path, cause = ce.Path, ce.Err
+		if errors.As(ce.Err, &pe) {
+			cause = fmt.Errorf("%s: %w", pe.Op, pe.Err)
+		}
+	case errors.As(err, &pe):
+		path, cause = pe.Path, fmt.Errorf("%s: %w", pe.Op, pe.Err)
+	default:
+		return err
 	}
-	return "duplicate: " + xdg.Abbrev(ce.Path) + ": " + cause
+	return shortenedErr{msg: xdg.Abbrev(path) + ": " + cause.Error(), err: err}
+}
+
+type shortenedErr struct {
+	msg string
+	err error
 }
 
+func (e shortenedErr) Error() string { return e.msg }
+func (e shortenedErr) Unwrap() error { return e.err }
+
 // dupIndex returns the shared *dup.Index for the resolved, sorted extra
 // directories named by key, building it exactly once across every
 // concurrent caller that asks for the same key.
@@ -263,7 +285,7 @@ func (f *facts) Duplicate(dirs []string) (string, bool, error) {
 	idx := f.run.dupIndex(key, sorted)
 	orig, isDup, err := idx.Lookup(f.file.Path)
 	if err != nil {
-		return "", false, err
+		return "", false, dupCause(err)
 	}
 	if !isDup {
 		return "", false, nil
diff --git a/internal/engine/match_test.go b/internal/engine/match_test.go
index 93311df..63bb54a 100644
--- a/internal/engine/match_test.go
+++ b/internal/engine/match_test.go
@@ -416,3 +416,47 @@ func TestDuplicateWarningsShareOneFormat(t *testing.T) {
 		}
 	}
 }
+
+// TestRuleDuplicateWarningShortensThePath: a duplicate check that fails on
+// the file itself is reported on the rule with the path shortened and not
+// repeated raw inside the cause, like the directory-level warnings (plan 11
+// review L7).
+func TestRuleDuplicateWarningShortensThePath(t *testing.T) {
+	if os.Getuid() == 0 {
+		t.Skip("root reads a chmod 000 file")
+	}
+	h := sandbox(t)
+	dl := filepath.Join(h, "dl")
+	os.MkdirAll(dl, 0o755)
+	old := time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC)
+	for _, n := range []string{"a.txt", "b.txt"} {
+		p := filepath.Join(dl, n)
+		os.WriteFile(p, []byte("same size"), 0o644)
+		os.Chtimes(p, old, old)
+	}
+	os.Chmod(filepath.Join(dl, "a.txt"), 0)
+	t.Cleanup(func() { os.Chmod(filepath.Join(dl, "a.txt"), 0o644) })
+	main := writeConfig(t, h, `(include "dl")`, map[string]string{"dl": "(path \"~/dl\")\n(rule \"dups\" (when (duplicate)) (move \"Dupes\"))\n"})
+	e, errs := Load(main)
+	if len(errs) > 0 {
+		t.Fatal(errs)
+	}
+	r, err := e.Match(context.Background(), e.Dirs[0])
+	if err != nil {
+		t.Fatal(err)
+	}
+	found := false
+	for _, fm := range append(append([]FileMatch{}, r.Matched...), r.Unmatched...) {
+		for _, w := range fm.Warnings {
+			if strings.Contains(w, h) {
+				t.Errorf("%s: warning repeats the raw path: %q", fm.File.Rel, w)
+			}
+			if w == "dups: duplicate check failed: ~/dl/a.txt: open: permission denied" {
+				found = true
+			}
+		}
+	}
+	if !found {
+		t.Errorf("no shortened rule warning for a.txt: %+v %+v", r.Matched, r.Unmatched)
+	}
+}