3 files changed, 51 insertions, 0 deletions
diff --git a/internal/cond/compile.go b/internal/cond/compile.go
index 4fdc75f..590d61a 100644
--- a/internal/cond/compile.go
+++ b/internal/cond/compile.go
@@ -362,6 +362,28 @@ func (c *compiler) compileMatched(n *sexp.Node) *node {
 	return &node{kind: kMatched, pos: n.Pos, label: "matched", cost: costCheap}
 }
 
+// collectNameGroups walks n and its children — and and or included, not
+// excluded — appending the capture-group count of every pattern of every
+// kName node reachable without crossing a not, in compile order. B1: a
+// name test under a not never supplies Result.Captures (eval.go's negated
+// tracking takes captures only when !negated), so it must not count toward
+// checkCaptures' "does some name test in this rule have enough groups"
+// either - a rule combining a capturing name test with an unrelated
+// (not (name ...)) must still pass.
+func collectNameGroups(n *node, out *[]int) {
+	if n == nil || n.kind == kNot {
+		return
+	}
+	if n.kind == kName {
+		for _, p := range n.patterns {
+			*out = append(*out, p.re.NumSubexp())
+		}
+	}
+	for _, ch := range n.children {
+		collectNameGroups(ch, out)
+	}
+}
+
 // quotedExampleErr records the shared "takes X in quotes: write (test
 // "arg")" diagnostic used by name, path, content and duplicate.
 func (c *compiler) quotedExampleErr(a *sexp.Node, test, noun string) {
diff --git a/internal/cond/compile_test.go b/internal/cond/compile_test.go
index e68a4d8..2a07ad6 100644
--- a/internal/cond/compile_test.go
+++ b/internal/cond/compile_test.go
@@ -124,6 +124,23 @@ func TestEmptyChildrenGuard(t *testing.T) {
 	}
 }
 
+// TestNameGroups: B1b - NameGroups() reports the capture-group count of
+// every name test reachable without crossing a not, and skips one reachable
+// only under a not (B1): here the outer (name ...) has two groups and the
+// (not (name ...)) one has one, but the result must carry only the outer's
+// count.
+func TestNameGroups(t *testing.T) {
+	c, errs := Compile("d.conf", nodes(t, `(and (name "inv-(\d+)-(\d+)") (not (name "draft-(\d+)")))`), Options{})
+	if len(errs) > 0 {
+		t.Fatal(errs)
+	}
+	got := c.NameGroups()
+	want := []int{2}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("NameGroups() = %v, want %v", got, want)
+	}
+}
+
 func TestGroupsMatchSpec(t *testing.T) {
 	want := map[string]string{
 		"image":        "jpg jpeg png gif webp bmp tif tiff heic heif avif svg ico raw cr2 nef arw dng",
diff --git a/internal/cond/types.go b/internal/cond/types.go
index 81c2f45..9455f63 100644
--- a/internal/cond/types.go
+++ b/internal/cond/types.go
@@ -93,6 +93,18 @@ type node struct {
 	dirs []string
 }
 
+// NameGroups returns the number of capture groups of every name test in the
+// condition that can ever supply captures, in compile order: a name test
+// nested inside and/or counts however deep, but one inside a not does not
+// (B1) - it can never be the source of Result.Captures, so it must not be
+// asked to justify a rule's use of {N} either. Empty when the rule has no
+// such name test.
+func (c *Cond) NameGroups() []int {
+	var out []int
+	collectNameGroups(c.root, &out)
+	return out
+}
+
 // groups maps a (type ...) group name to the extensions it expands to,
 // spec Appendix A.
 var groups = map[string][]string{