From 24a84671ace373ae331fa83a1ff484990f4dff0e Mon Sep 17 00:00:00 2001
From: Lukasz Kasprzak <lukas@labunix.xyz>
Date: Sat, 12 Sep 2026 12:58:14 +0200
Subject: krino: planning — chains, placeholders, conflicts, JSON
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---
 internal/engine/engine.go | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

(limited to 'internal/engine/engine.go')

diff --git a/internal/engine/engine.go b/internal/engine/engine.go
index eec9a60..ea61e8c 100644
--- a/internal/engine/engine.go
+++ b/internal/engine/engine.go
@@ -6,6 +6,7 @@
 package engine
 
 import (
+	"fmt"
 	"os"
 	"time"
 
@@ -13,6 +14,7 @@ import (
 	"krino/internal/config"
 	"krino/internal/extract"
 	"krino/internal/ignore"
+	"krino/internal/plan"
 )
 
 // Engine holds a loaded, compiled configuration: everything a front end
@@ -84,6 +86,10 @@ func Load(mainFile string, names ...string) (*Engine, []*config.Diag) {
 				errs = append(errs, cerrs...)
 				continue
 			}
+			if diag := checkCaptures(d.File, r, c); diag != nil {
+				errs = append(errs, diag)
+				continue
+			}
 			dir.Rules = append(dir.Rules, &Rule{Name: r.Name, Conf: r, Settings: rs, Cond: c})
 		}
 		dir.ContentVariants = contentVariants(dir.Rules)
@@ -102,6 +108,38 @@ func Load(mainFile string, names ...string) (*Engine, []*config.Diag) {
 	}, nil
 }
 
+// checkCaptures validates a compiled rule's actions against the capture
+// groups its own name tests can supply (spec 7.3): a rule using {N} needs a
+// name test at all, and every name test in it needs at least N groups. It
+// reports only the first offending action, so one config mistake yields one
+// diagnostic.
+func checkCaptures(file string, r *config.Rule, c *cond.Cond) *config.Diag {
+	groups := c.NameGroups()
+	for _, a := range r.Actions {
+		n, err := plan.MaxIndex(a.Arg)
+		if err != nil || n == 0 {
+			continue
+		}
+		if len(groups) == 0 {
+			return &config.Diag{File: file, Pos: a.Pos, Msg: fmt.Sprintf("rule %q: {%d} needs a name test to capture from", r.Name, n)}
+		}
+		for _, g := range groups {
+			if g < n {
+				return &config.Diag{File: file, Pos: a.Pos, Msg: fmt.Sprintf("rule %q: {%d} but a name test has only %s", r.Name, n, captureGroups(g))}
+			}
+		}
+	}
+	return nil
+}
+
+// captureGroups renders a capture-group count with correct singular/plural.
+func captureGroups(n int) string {
+	if n == 1 {
+		return "1 capture group"
+	}
+	return fmt.Sprintf("%d capture groups", n)
+}
+
 // dedupeNames returns names with every repeat after its first occurrence
 // removed, order preserved.
 func dedupeNames(names []string) []string {
-- 
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