Check that a change to predefined.json removes no key a module still names

Part 2 of 2: the check merge-check.sh runs, and its tests with a planted removal (hq ADR 0348 clause 7, issue 661).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

checks/predefined/main.go

@@ -0,0 +1,153 @@
+// Command predefined refuses a change to predefined.json that removes a key a module still names (novox/hq ADR
+// 0348 clause 7, design 57 package K2, issue 661).
+//
+// Mesh config and node config hold values only for the keys on the catalogue's list of predefined keys, at the
+// root of the repository; a module's config value may fall back to one, `"predefined": "<key>"`. A key removed
+// while a manifest still names it would leave that module falling back to nothing: the controller refuses its
+// build then, at the next merge that touches it. So the removal is refused here, in the pull request that makes
+// it, naming each module that names the key.
+//
+// **What it cannot know.** Whether a key still holds a value at the mesh or a node is mesh-config's to say (design
+// 57 package K3): it holds the values, and the catalogue's check reads no store. Until mesh-config refuses that
+// itself, removing a key nobody names is let through here, and said.
+//
+// The list it compares with is the trunk's at the merge base, given with -base; without one, nothing was removed.
+// The controller the mesh runs reads the list itself (type, validation, every manifest against it) in the
+// module check; this check reads only its keys.
+//
+//	go run . [-base <the trunk's predefined.json>] <catalogue root>
+//
+// Exits 1 on a finding.
+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+)
+
+// File is the list's file at the root of the catalogue.
+const File = "predefined.json"
+
+// Keys is the keys of a list, read as a JSON object; an absent file has none.
+func Keys(path string) (map[string]bool, error) {
+	raw, err := os.ReadFile(path)
+	if errors.Is(err, fs.ErrNotExist) {
+		return map[string]bool{}, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	var keys map[string]json.RawMessage
+	if err := json.Unmarshal(raw, &keys); err != nil {
+		return nil, fmt.Errorf("%s is not a JSON object of keys: %w", path, err)
+	}
+	out := map[string]bool{}
+	for k := range keys {
+		out[k] = true
+	}
+	return out, nil
+}
+
+// Named is, per predefined key, the modules whose manifests name it: under `config`, or its alias `settings`.
+func Named(root string) (map[string][]string, error) {
+	manifests, err := filepath.Glob(filepath.Join(root, "modules", "*", "module.json"))
+	if err != nil {
+		return nil, err
+	}
+	sort.Strings(manifests)
+	named := map[string][]string{}
+	for _, path := range manifests {
+		raw, err := os.ReadFile(path)
+		if err != nil {
+			return nil, err
+		}
+		var m struct {
+			Module   string                     `json:"module"`
+			Config   map[string]json.RawMessage `json:"config"`
+			Settings map[string]json.RawMessage `json:"settings"`
+		}
+		if err := json.Unmarshal(raw, &m); err != nil {
+			return nil, fmt.Errorf("%s: %w", path, err)
+		}
+		for _, declared := range []map[string]json.RawMessage{m.Config, m.Settings} {
+			for _, d := range declared {
+				var value struct {
+					Predefined string `json:"predefined"`
+				}
+				if json.Unmarshal(d, &value) == nil && value.Predefined != "" {
+					named[value.Predefined] = append(named[value.Predefined], m.Module)
+				}
+			}
+		}
+	}
+	return named, nil
+}
+
+// Removed is each key the base list holds and the tree's does not, with the modules still naming it; a removed
+// key nobody names is answered with none.
+func Removed(base, tree map[string]bool, named map[string][]string) map[string][]string {
+	out := map[string][]string{}
+	for k := range base {
+		if !tree[k] {
+			out[k] = named[k]
+		}
+	}
+	return out
+}
+
+func main() {
+	basePath := flag.String("base", "", "the trunk's predefined.json at the merge base")
+	flag.Parse()
+	if flag.NArg() != 1 {
+		fmt.Fprintln(os.Stderr, "usage: predefined [-base <the trunk's predefined.json>] <catalogue root>")
+		os.Exit(2)
+	}
+	root := flag.Arg(0)
+	tree, err := Keys(filepath.Join(root, File))
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+	if *basePath == "" {
+		fmt.Printf("%s: %d key(s); no trunk list given, so none was removed\n", File, len(tree))
+		return
+	}
+	base, err := Keys(*basePath)
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+	named, err := Named(root)
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+	removed := Removed(base, tree, named)
+	keys := make([]string, 0, len(removed))
+	for k := range removed {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	failed := false
+	for _, k := range keys {
+		if modules := removed[k]; len(modules) > 0 {
+			failed = true
+			fmt.Printf("%s: the key %q is removed and still named by %s: move each off it first (novox/hq ADR 0348 "+
+				"clause 7)\n", File, k, strings.Join(modules, ", "))
+		} else {
+			fmt.Printf("%s: the key %q is removed and no module names it; whether the mesh or a node still holds a "+
+				"value for it is mesh-config's to refuse, not this check's\n", File, k)
+		}
+	}
+	if failed {
+		os.Exit(1)
+	}
+	fmt.Printf("%s: %d key(s), none removed that a module names\n", File, len(tree))
+}