From e0c82440b39b11bc6523ce1998176c45a2e396fa Mon Sep 17 00:00:00 2001
From: Lilleman auf Larv <lilleman@larvit.se>
Date: Mon, 21 Sep 2026 18:36:31 +0200
Subject: [PATCH] Hold every source file to a README Layout line

---
 doc_test.go    |  9 +++++++--
 readme_test.go | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/doc_test.go b/doc_test.go
index 55d8b1a..4952312 100644
--- a/doc_test.go
+++ b/doc_test.go
@@ -47,15 +47,20 @@ func namesAPass(t *testing.T, where, text string, declared, funcs map[string]boo
 	}
 }
 
-func sourceFiles(t *testing.T) (*token.FileSet, []*ast.File) {
+func goFiles(t *testing.T) []string {
 	t.Helper()
 	pkg, err := build.ImportDir(".", 0)
 	if err != nil {
 		t.Fatalf("read the package directory: %v", err)
 	}
+	return pkg.GoFiles
+}
+
+func sourceFiles(t *testing.T) (*token.FileSet, []*ast.File) {
+	t.Helper()
 	fset := token.NewFileSet()
 	var files []*ast.File
-	for _, name := range pkg.GoFiles {
+	for _, name := range goFiles(t) {
 		f, err := parser.ParseFile(fset, name, nil, parser.ParseComments)
 		if err != nil {
 			t.Fatalf("parse %s: %v", name, err)
diff --git a/readme_test.go b/readme_test.go
index c253170..a8238f8 100644
--- a/readme_test.go
+++ b/readme_test.go
@@ -4,12 +4,14 @@ import (
 	"encoding/json"
 	"os"
 	"regexp"
+	"slices"
 	"strings"
 	"testing"
 )
 
 var (
 	jsonBlock  = regexp.MustCompile("(?s)```json\n(.*?)```")
+	plainBlock = regexp.MustCompile("(?s)```\n(.*?)```")
 	tsvBlock   = regexp.MustCompile("(?s)```tsv\n(.*?)```")
 	rowsFile   = regexp.MustCompile(`"rows":\s*"([^"]+)"`)
 	parentName = regexp.MustCompile(`"parent":\s*"([^"]+)"`)
@@ -191,3 +193,38 @@ func TestReadmeTableExample(t *testing.T) {
 		t.Fatalf("README table example as a record: %q, %v", r.CSVHeader(), err)
 	}
 }
+
+// TestLayoutNamesEverySourceFile holds an added, renamed or split file to its Layout
+// line, so the list a reader picks a file from stays the list on disk.
+func TestLayoutNamesEverySourceFile(t *testing.T) {
+	src := readme(t)
+	i := strings.Index(src, "## Layout")
+	if i < 0 {
+		t.Fatal("README lost the Layout section")
+	}
+	block := plainBlock.FindStringSubmatch(src[i:])
+	if block == nil {
+		t.Fatal("README Layout section has no block")
+	}
+	listed := map[string]bool{}
+	for _, line := range strings.Split(block[1], "\n") {
+		name, _, _ := strings.Cut(strings.TrimSpace(line), " ")
+		if strings.HasSuffix(name, ".go") {
+			listed[name] = true
+		}
+	}
+	for _, name := range goFiles(t) {
+		if !listed[name] {
+			t.Errorf("the README Layout names no %s, so nothing says what it holds", name)
+		}
+		delete(listed, name)
+	}
+	stale := make([]string, 0, len(listed))
+	for name := range listed {
+		stale = append(stale, name)
+	}
+	slices.Sort(stale)
+	for _, name := range stale {
+		t.Errorf("the README Layout names %s, which the package does not hold", name)
+	}
+}