Answer architecture round 6: a manifest's reads names namespaces, loadReached notes only those nothing loaded provides, a mounted module labels its files by its namespace, Source.Load checks its mount, and the README keeps namespace and reads in an edited copy

CHANGELOG.md

@@ -131,9 +131,9 @@ replacement, and each removed path, column or flag.
   and the CLI carries them all. `New` loads the modules `WithDataFS(modules...)` names and
   the folders `WithDataPath` names, and fails, naming `WithDataFS`, where no such option
   is given. A manifest's `namespace` mounts its source under a dot path, and its `reads` lists the
-  modules its source reads by default; a reference to a path nothing provides fails to
-  load, asking whether a module is missing and naming every module the loaded manifests
-  read, or saying there are none.
+  namespaces of the modules its source reads by default; a reference to a path nothing
+  provides fails to load, asking whether a module is missing and naming each namespace
+  read that nothing loaded provides, or saying no loaded manifest names a module to add.
 - A data source whose root holds a `.fejkdata.json` manifest with an `index` loads each
   category on the first call reaching it, as each shipped module does. Data failing to load,
   in `New` or on that first call, gives an error matching `ErrLoad`, and the CLI exits 1.

README.md

@@ -184,23 +184,24 @@ every category of its source, so a category file it leaves out never loads.
 The index maps each category's dot path to an entry: `parent`, the table it links to,
 which needs its own entry in the same folder; and `paths`, every path `List` advertises
 below the category, `""` for the category itself. Each shipped module's manifest, such as
-[`data/svse/.fejkdata.json`](data/svse/.fejkdata.json), is one, so delete it from a
-copy you edit, or keep its index current. A table whose parent column differs from its
-entry's `parent` fails at first reach, and a table linking under another source's table
-needs a source without an index. `//go:embed` of a directory leaves the manifest out, and
-the source then loads whole in `New`; name it in the pattern too.
+[`data/svse/.fejkdata.json`](data/svse/.fejkdata.json), carries one, so in a copy you
+edit, delete its `index` and keep its `namespace` and `reads`, or keep the index current.
+A table whose parent column differs from its entry's `parent` fails at first reach, and a
+table linking under another source's table needs a source without an index. `//go:embed`
+of a directory leaves the manifest out, and the source then loads whole in `New` and at
+the root, with no `namespace`; name the manifest in the pattern too.
 
 A manifest's `namespace` is the dot path its source's root sits under: a folder holding
 `person.json` with `"namespace": "sv_SE"` provides `sv_SE.person`, its subfolders adding
 segments below that. Each shipped module carries one, so `data/svse/person.json` is
 `sv_SE.person`.
 
-A manifest's `reads` lists, by any name its author chooses, every module the source's
-references read unless another source provides the same paths, directly or through
-another module. Nothing loads these modules: pass them yourself. A shipped module names a
-Go package: `svse`'s manifest reads `github.com/larvit/fejkdata/data/geose`. Data whose
-reference names a path nothing provides fails to load, asking whether a module is
-missing and naming every module the loaded manifests read, or saying they name none.
+A manifest's `reads` lists the namespace of every module the source's references read
+unless another source provides the same paths, directly or through another module.
+Nothing loads these modules: pass them yourself. `svse`'s manifest reads `geo.SE`. Data
+whose reference names a path nothing provides fails to load; where a namespace the loaded
+manifests read is one nothing loaded provides, the error asks whether a module is missing
+and names it, and otherwise it says no loaded manifest names a module to add.
 `namespace` and `reads` need no index.
 
 Each locale carries `address`, `color`, `company`, `date`, `email`, `first-name`,
@@ -305,7 +306,7 @@ What the two locales do not share: `en_US.address` carries a `region` column the
 one has no use for, and `sv_SE.title` has no `parent`, so it is selected as
 `sv_SE.title[dr]` rather than inside a sex.
 
-A `geo` folder holds one tree per country under its alpha-2 code: five
+The `geo` namespace holds one tree per country under its alpha-2 code: five
 [linked tables](#linked-tables) named alike, and an `address` record binding one locality
 and drawing its street and postal code inside it. The locale's `address` prints that
 record, and each of its columns describes the address printed. Do not assert that a Swedish
@@ -377,7 +378,7 @@ import (
 f, err := fejkdata.New(fejkdata.WithDataFS(svse.FS, geose.FS))
 ```
 
-`enus` reads `geous`; `misc` reads none. `New` fails where no `WithDataFS` or
+`enus` reads `geous`; `misc` and the geo packages read none. `New` fails where no `WithDataFS` or
 `WithDataPath` names the data to load.
 
 `New` refuses data that breaks the grammar, could mean two things or cannot render a valid

data.go

@@ -9,12 +9,12 @@ import (
 
 // loadSources merges sources in order, the last winning a clash. A source whose manifest
 // carries an index leaves its categories unloaded; every other source loads here, with
-// the unloaded categories it needs. It also returns, sorted, every module the sources'
-// manifests read by default.
+// the unloaded categories it needs. It also returns, sorted, every namespace the sources'
+// manifests read.
 // docs/decisions.md#a-source-whose-manifest-carries-an-index-loads-each-category-on-first-reach-any-other-loads-in-new-with-what-it-reads
 func loadSources(sources []datafiles.Source) (folder, []string, error) {
 	root := folder{children: map[string]node{}}
-	var modules []string
+	var reads []string
 	for _, src := range sources {
 		m, err := src.Manifest()
 		if err != nil {
@@ -23,14 +23,14 @@ func loadSources(sources []datafiles.Source) (folder, []string, error) {
 		if err := addSource(&root, src, m); err != nil {
 			return folder{}, nil, err
 		}
-		for _, module := range m.Reads {
-			if !slices.Contains(modules, module) {
-				modules = append(modules, module)
+		for _, namespace := range m.Reads {
+			if !slices.Contains(reads, namespace) {
+				reads = append(reads, namespace)
 			}
 		}
 	}
-	slices.Sort(modules)
-	return root, modules, loadReached(&root, categorySites(&root), nil)
+	slices.Sort(reads)
+	return root, reads, loadReached(&root, reads, categorySites(&root), nil)
 }
 
 func addSource(root *folder, src datafiles.Source, m datafiles.Manifest) error {

data/enus/.fejkdata.json

@@ -24,5 +24,5 @@
 		"en_US.word": {"paths":[""]}
 	},
 	"namespace": "en_US",
-	"reads": ["github.com/larvit/fejkdata/data/geous"]
+	"reads": ["geo.US"]
 }

data/svse/.fejkdata.json

@@ -24,5 +24,5 @@
 		"sv_SE.word": {"paths":[""]}
 	},
 	"namespace": "sv_SE",
-	"reads": ["github.com/larvit/fejkdata/data/geose"]
+	"reads": ["geo.SE"]
 }

docs/decisions.md

@@ -140,7 +140,7 @@ A directory a machine happens to have would make `--seed 42` machine-dependent;
 
 2026-10-04, Lilleman auf Larv; revised 2026-10-09 to put the packages in the core's Go module. Serves goals 2.3, 6.2, 7.3, 9 and 10.1. Carried out by `todo.md` items 181, 184, 185 and 186. The CLI binary may grow to hundreds of MB.
 
-- One Go package per locale, one per country's `geo/` tree, and one for `misc`, all in the core's Go module. A package registers nothing when imported.
+- One Go package per locale, one per country's `geo` tree, and one for `misc`, all in the core's Go module. A package registers nothing when imported.
 - A bare `New()` loads no data and fails, naming the option to add. `WithoutShippedData` goes.
 - A data package's `FS` is an `fs.FS` passed to `WithDataFS`, as anyone's data is, and `New` takes several. It is an exported `var FS embed.FS`, the shape `//go:embed` gives; a function returning it would only stop a program reassigning the FS variable of a package it imports. A module carrying functions loads through an option of its own, so a data module that starts carrying functions breaks its users. Such a function reaches the randomness through an interface the root declares; `internal/drawstate`'s type stays internal.
 - A module names, in a manifest, every module it reads by default, directly or through another, so the first error names the whole set to import. A manifest is optional: a `--data-path` folder without one is a module. Nothing loads a default on its own.
@@ -160,7 +160,9 @@ custom-CLI builder. Serves goals 1 and 3.3. `sv_SE` ships as `data/svse`, `en_US
 Go linters flag a capital or an underscore in a package name, and `SE.FS` read as a type.
 Each package holds its files at its root, and its manifest's `namespace` puts them under
 the namespace, so no path repeats it. The bench also chose `reads` for what a module reads
-by default and the wording of the errors naming it. Valid until a locale's lowered name
+by default and the wording of the errors naming it. A `reads` entry is a namespace, so the
+error names only what nothing loaded provides, and with every module loaded a typo names
+none. Valid until a locale's lowered name
 clashes with another's.
 
 ## A source whose manifest carries an index loads each category on first reach; any other loads in `New`, with what it reads
@@ -592,7 +594,7 @@ when a source carries it.
 
 2026-09-24, Lilleman auf Larv; revised 2026-10-10, when the shipped data became Go packages.
 Serves goal 6.2. `svse.FS` loads alone, and `sv_SE.address` then fails at first reach,
-naming `github.com/larvit/fejkdata/data/geose`, which `svse`'s manifest reads.
+naming `geo.SE`, which `svse`'s manifest reads and nothing loaded provides.
 `New` does not check that each module a manifest reads was given. A check by module name
 would refuse a stand-in providing the same paths (goal 9.2). A check by path needs every
 reference, and only loading each indexed category finds them, which goal 13 rules out.

fejkdata.go

@@ -31,15 +31,15 @@ type Generator struct {
 	drawState *drawstate.State
 	root      folder // the categories as the node a path walks from, owned here so a walk allocates none
 	structs   map[reflect.Type]structResult
-	// defaultModules is every module the loaded sources' manifests read by default.
-	defaultModules []string
+	// manifestReads is every namespace the loaded sources' manifests read.
+	manifestReads []string
 }
 
 type config struct {
 	seed       uint64
 	seeded     bool
 	sources    []datafiles.Source
-	err     error
+	nilModules error
 	// given is whether an option named the data to load, though it may name none.
 	given bool
 }
@@ -69,7 +69,7 @@ func WithDataFS(modules ...fs.FS) Option {
 	return func(c *config) {
 		for i, fsys := range modules {
 			if fsys == nil {
-				c.err = errors.Join(c.err, fmt.Errorf("fejkdata: WithDataFS module %d is nil", i+1))
+				c.nilModules = errors.Join(c.nilModules, fmt.Errorf("fejkdata: WithDataFS module %d is nil", i+1))
 				continue
 			}
 			c.sources = append(c.sources, datafiles.FS(fsys))
@@ -106,18 +106,18 @@ func New(opts ...Option) (*Generator, error) {
 	if !c.given {
 		return nil, errNoData
 	}
-	if c.err != nil {
-		return nil, c.err
+	if c.nilModules != nil {
+		return nil, c.nilModules
 	}
-	root, modules, err := loadSources(c.sources)
+	root, reads, err := loadSources(c.sources)
 	if err != nil {
-		return nil, fmt.Errorf("fejkdata: %w", withDefaultModules(loadError{err}, modules))
+		return nil, fmt.Errorf("fejkdata: %w", loadError{err})
 	}
 	seed, err := c.drawSeed()
 	if err != nil {
 		return nil, fmt.Errorf("fejkdata: %w", err)
 	}
-	return &Generator{drawState: drawstate.New(seed), root: root, defaultModules: modules}, nil
+	return &Generator{drawState: drawstate.New(seed), root: root, manifestReads: reads}, nil
 }
 
 // List returns the sorted dotted paths Fake renders: each category and every field,

index.go

@@ -58,8 +58,8 @@ func (f *Generator) loadCallerPath(path string) (string, []string, error) {
 		return "", nil, fmt.Errorf("fejkdata: %w", err)
 	}
 	if c, ok := categoryOn(&f.root, segs); ok && c.unloaded() {
-		if err := loadReached(&f.root, nil, []categoryAt{c}); err != nil {
-			return "", nil, fmt.Errorf("fejkdata: %w", withDefaultModules(loadError{err}, f.defaultModules))
+		if err := loadReached(&f.root, f.manifestReads, nil, []categoryAt{c}); err != nil {
+			return "", nil, fmt.Errorf("fejkdata: %w", loadError{err})
 		}
 	}
 	return path, segs, nil
@@ -105,8 +105,9 @@ func needs(root *folder, s categorySite) []categoryAt {
 
 // loadReached loads the unloaded categories among wanted and every unloaded category they
 // or sites need, then runs sites and all it loaded through a whole load's pipeline. On an
-// error it puts back what it loaded, so the next call fails the same way.
-func loadReached(root *folder, sites []categorySite, wanted []categoryAt) error {
+// error it puts back what it loaded, so the next call fails the same way, and notes which
+// namespace of reads, every namespace the loaded manifests read, nothing in root provides.
+func loadReached(root *folder, reads []string, sites []categorySite, wanted []categoryAt) error {
 	queue := wanted
 	for _, s := range sites {
 		queue = append(queue, needs(root, s)...)
@@ -118,8 +119,9 @@ func loadReached(root *folder, sites []categorySite, wanted []categoryAt) error
 	}
 	if err != nil {
 		b.putBack()
+		return withMissingModules(err, root, reads)
 	}
-	return err
+	return nil
 }
 
 // batch is the categories one loadReached loaded, each beside the entry it was loaded from.

inline.go

@@ -36,8 +36,8 @@ func (f *Generator) NewTemplate(input string) (*Template, error) {
 	}
 	f.mu.Lock()
 	defer f.mu.Unlock()
-	if err := loadInline(&f.root, n, "template", false); err != nil {
-		return nil, f.noDataNote(fmt.Errorf("fejkdata: %w", withDefaultModules(err, f.defaultModules)))
+	if err := loadInline(&f.root, f.manifestReads, n, "template", false); err != nil {
+		return nil, f.noDataNote(fmt.Errorf("fejkdata: %w", err))
 	}
 	return &Template{g: f, n: n}, nil
 }
@@ -84,13 +84,14 @@ func inputValue(input string) jsonvalue.Value {
 	return raw
 }
 
-// loadInline loads the unloaded categories n reads, then runs n through the pipeline against root.
-func loadInline(root *folder, n node, label string, typedByGo bool) error {
+// loadInline loads the unloaded categories n reads, then runs n through the pipeline against root;
+// reads is every namespace the loaded manifests read.
+func loadInline(root *folder, reads []string, n node, label string, typedByGo bool) error {
 	nodes := inlineNodes(n, label)
 	if err := refuseFolderRefs(nodes); err != nil {
 		return err
 	}
-	if err := loadReached(root, nil, referenced(root, nil, nodes)); err != nil {
+	if err := loadReached(root, reads, nil, referenced(root, nil, nodes)); err != nil {
 		return loadError{err}
 	}
 	return pipeline{

internal/datafiles/datafiles.go

@@ -6,6 +6,7 @@ import (
 	"io/fs"
 	"os"
 	"path"
+	"slices"
 	"strings"
 
 	"github.com/larvit/fejkdata/internal/grammar"
@@ -30,10 +31,15 @@ func Dir(path string) Source {
 // FS is the tree in fsys.
 func FS(fsys fs.FS) Source { return Source{fsys: fsys} }
 
-// Mounted is s with its root under the dot path namespace, "" for the namespace's root.
+// Mounted is s with its root under the dot path namespace, "" for the namespace's root. A
+// source with no label of its own names its files in errors by the namespace's folders.
 func (s Source) Mounted(namespace string) Source {
-	if namespace != "" {
+	if namespace == "" {
+		return s
+	}
 	s.mount = strings.Split(namespace, ".")
+	if s.label == "" {
+		s.label = path.Join(s.mount...)
 	}
 	return s
 }
@@ -139,6 +145,9 @@ func (s Source) walkFolder(dir []string, compile func(Category) error) (bool, er
 // Load hands compile the category file name.json in the folder dir of the namespace, which
 // lies under the source's mount.
 func (s Source) Load(dir []string, name string, compile func(Category) error) error {
+	if len(dir) < len(s.mount) || !slices.Equal(dir[:len(s.mount)], s.mount) {
+		return fmt.Errorf("%s.%s lies outside the namespace %s", strings.Join(dir, "."), name, strings.Join(s.mount, "."))
+	}
 	full := s.dirPath(dir[len(s.mount):])
 	entries, err := fs.ReadDir(s.fsys, full)
 	if err != nil {

internal/datafiles/manifest.go

@@ -17,12 +17,12 @@ const ManifestFile = ".fejkdata.json"
 // Manifest is what a source's manifest says of it.
 type Manifest struct {
 	// Index is every category of the source by dot path; nil where the manifest has none.
-	Index map[string]IndexEntry `json:"index"`
-	// Reads is every module the source reads by default, directly or through another;
-	// nothing loads them.
-	Reads []string `json:"reads"`
+	Index map[string]IndexEntry
 	// Namespace is the dot path the source's root sits under, "" for the namespace's root.
-	Namespace string `json:"namespace"`
+	Namespace string
+	// Reads is the namespace of every module the source reads unless another source
+	// provides the same paths, directly or through another; nothing loads them.
+	Reads []string
 }
 
 // IndexEntry is what an index says of a category: its parent table, "" for none, and the
@@ -108,7 +108,7 @@ func decodeNamespace(v any) (string, error) {
 	return namespace, nil
 }
 
-// decodeReads decodes the modules a source reads, each named by a non-empty string.
+// decodeReads decodes the namespaces of the modules a source reads.
 func decodeReads(v any) ([]string, error) {
 	items, isList := v.([]any)
 	if !isList {
@@ -118,17 +118,17 @@ func decodeReads(v any) ([]string, error) {
 	seen := map[string]bool{}
 	var errs []error
 	for i, item := range items {
-		module, isString := item.(string)
+		namespace, isString := item.(string)
 		switch {
 		case !isString:
 			errs = append(errs, fmt.Errorf("reads item %d must be a string, not %s", i+1, jsonvalue.Kind(item)))
-		case module == "":
-			errs = append(errs, fmt.Errorf("reads item %d is empty; it names a module", i+1))
-		case seen[module]:
-			errs = append(errs, fmt.Errorf("reads item %d repeats %q", i+1, module))
+		case checkCategoryPath(namespace) != nil:
+			errs = append(errs, fmt.Errorf("reads item %d: %w", i+1, checkCategoryPath(namespace)))
+		case seen[namespace]:
+			errs = append(errs, fmt.Errorf("reads item %d repeats %q", i+1, namespace))
 		default:
-			seen[module] = true
-			out = append(out, module)
+			seen[namespace] = true
+			out = append(out, namespace)
 		}
 	}
 	return out, errors.Join(errs...)

reference.go

@@ -121,17 +121,25 @@ type noEntry struct{ seg string }
 
 func (e noEntry) Error() string { return fmt.Sprintf("no entry %q", e.seg) }
 
-// withDefaultModules adds to err, where data fails to load because a segment names nothing, the
-// modules the loaded sources' manifests read by default, or that they name none.
-func withDefaultModules(err error, modules []string) error {
+// withMissingModules adds to err, where a path names nothing, each namespace of reads that
+// nothing in root provides, as the modules a loaded manifest reads and none loaded; or else
+// that no loaded manifest names a module to add, the mistake being the path's own.
+func withMissingModules(err error, root *folder, reads []string) error {
 	var ne noEntry
-	if !errors.Is(err, ErrLoad) || !errors.As(err, &ne) {
+	if !errors.As(err, &ne) {
 		return err
 	}
-	if len(modules) == 0 {
+	var missing []string
+	for _, namespace := range reads {
+		segs := strings.Split(namespace, ".")
+		if _, i := folderAt(root, segs); i < len(segs) {
+			missing = append(missing, namespace)
+		}
+	}
+	if len(missing) == 0 {
 		return fmt.Errorf("%w, and no loaded manifest names a module to add", err)
 	}
-	return fmt.Errorf("%w; is a module missing? The loaded modules read %s", err, strings.Join(modules, ", "))
+	return fmt.Errorf("%w; is a module missing? The loaded modules read %s, which nothing loaded provides", err, strings.Join(missing, ", "))
 }
 
 // noDataNote adds to err, where a segment names nothing and f holds no data at all, that no

struct.go

@@ -31,7 +31,7 @@ func (f *Generator) FakeStruct(v any) error {
 	defer f.mu.Unlock()
 	shape, err := f.structShapeOf(p.Elem().Type())
 	if err != nil {
-		return fmt.Errorf("fejkdata: %w", withDefaultModules(err, f.defaultModules))
+		return fmt.Errorf("fejkdata: %w", err)
 	}
 	shape.fill(f.drawState, p.Elem())
 	return nil
@@ -55,7 +55,7 @@ func (f *Generator) structShapeOf(t reflect.Type) (*structShape, error) {
 	if label == "" {
 		label = "struct"
 	}
-	sc := &structCompile{root: &f.root, visiting: map[reflect.Type]bool{}, structsLeft: maxStructs}
+	sc := &structCompile{root: &f.root, reads: f.manifestReads, visiting: map[reflect.Type]bool{}, structsLeft: maxStructs}
 	shape, err := sc.compileShape(t, label)
 	if f.structs == nil {
 		f.structs = map[reflect.Type]structResult{}
@@ -85,6 +85,7 @@ func (s *structShape) empty() bool { return s.record == nil && len(s.nested) ==
 // rather than filled without end, and how many more structs it may walk.
 type structCompile struct {
 	root        *folder
+	reads       []string
 	visiting    map[reflect.Type]bool
 	structsLeft int
 }
@@ -111,7 +112,7 @@ func (sc *structCompile) compileShape(t reflect.Type, label string) (*structShap
 		return nil, err
 	}
 	if len(c.tags) > 0 {
-		if err := c.shape.compileRecord(sc.root, t, label, c.tags); err != nil {
+		if err := c.shape.compileRecord(sc.root, sc.reads, t, label, c.tags); err != nil {
 			return nil, err
 		}
 	}
@@ -255,13 +256,13 @@ func checkTaggedType(sf reflect.StructField) error {
 
 // compileRecord compiles the tagged fields of t as one record, and proves each column holds
 // only what its field's Go type can.
-func (s *structShape) compileRecord(root *folder, t reflect.Type, label string, tags map[string]jsonvalue.Value) error {
+func (s *structShape) compileRecord(root *folder, reads []string, t reflect.Type, label string, tags map[string]jsonvalue.Value) error {
 	tags["format"] = jsonvalue.String("")
 	n, err := compileFrom(jsonvalue.Object(tags), atGoTop)
 	if err != nil {
 		return fmt.Errorf("%s: %w", label, err)
 	}
-	if err := loadInline(root, n, label, true); err != nil {
+	if err := loadInline(root, reads, n, label, true); err != nil {
 		return err
 	}
 	record, err := recordOf(n)