fix(lang): 0.R4 - ludic.ui's UiAct is its own, and a name that meets a package's export says whose it is

A game's exported UiAct collided with ludic.ui's, which nothing outside ludic.ui uses: it is private
to ludic.ui now, and a private record of one spelling in two modules never clashed. A real clash - a
type named like one a package exports - is still refused, and the message names the package and the
way out (`ludic_ui exports it, and exported names are one namespace - rename this one, or declare it
without export inside a module of your own`).

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

LANGUAGE.md

@@ -119,7 +119,10 @@ show.
 The same holds for a `property` and an `event`: `fishing` and `hunting` may each have a private
 `Catch` record and a private `Landed` event with different fields, and each module's types, `new`,
 `emit` and `@On` reach its own (compiled as `Catch__fishing`). Two exported ones of one spelling are
-refused (`'Catch' is defined twice`, `event 'Landed' is defined twice`). Three kinds of record stay
+refused (`'Catch' is defined twice`, `event 'Landed' is defined twice`). When one of the two is a package's export the message
+says so (`'UiNode' is defined twice (...): ludic_ui exports it, and exported names are one namespace -
+rename this one, or declare it without export inside a module of your own`); a package exports only
+what a program uses, so ludic.ui's `UiAct` is its own and a game's may take the name. Three kinds of record stay
 one namespace, because other code names them by spelling: a generic record, a property that is an
 entity's component (a `model` names it), and the record a component or a view generates.
 

changes/package-export-clash.md

@@ -0,0 +1,8 @@
+bump: patch
+type: fix
+**A name that meets a package's export says whose it is; ludic.ui's `UiAct` is its own.** A game's
+`UiAct` collided with ludic.ui's, which no program uses - it is private to ludic.ui now, so the game
+may have one. A real clash - a type named like one a package exports - is still refused, and the
+message names the package and the way out: `'UiNode' is defined twice (...): ludic_ui exports it, and
+exported names are one namespace - rename this one, or declare it without export inside a module of
+your own`.

examples/modules/own_uiact.ludic

@@ -0,0 +1,7 @@
+# own_uiact.ludic - a game module may export a record named like one of ludic.ui's own private ones
+import "ludic.ui"
+import "own_uiact/acts"
+program OwnUiAct {
+  numbers float
+  entry { print(`{act_kind()}`) }
+}

examples/modules/own_uiact/acts/index.ludic

@@ -0,0 +1,6 @@
+module acts
+export property UiAct { kind: int = 3 }
+export function act_kind() -> int {
+  let a = new UiAct
+  return a.kind
+}

examples/rejected/pkg_export_clash.ludic

@@ -0,0 +1,7 @@
+# a program's type named like a package's export is a real clash, and the message says whose
+import "ludic.ui"
+program PkgClash {
+  numbers float
+  property UiNode { kind: int = 3 }
+  entry { print("x") }
+}

packages/ludic.ui/act.ludic

@@ -4,7 +4,7 @@
 const A_CALL: int = 0
 const A_SET: int = 1
 const A_EMIT: int = 2
-export property UiAct {
+property UiAct {
   kinds: []int = null
   names: []string = null
   exprs: []UiExpr = null

selfhost/backend/emit_decl.ludic

@@ -239,6 +239,15 @@ function decl_group(k: int) -> int {
   if k == N_STRUCT or k == N_COMP or k == N_EVENT { return 2 }
   return 0
 }
+# when one of the two is a package's export: say so, and what to do - exported names are one
+# namespace, and a module's private one of the same spelling would not clash
+function dup_whose(first: Node, d: Node) -> pointer {
+  var pk = pkg_of_file(first.file)
+  if pk == "" { pk = pkg_of_file(d.file) }
+  if pk == "" { return "" }
+  if not (pkg_of_file(first.file) == "") and not (pkg_of_file(d.file) == "") { return "" }
+  return `: {pk} exports it, and exported names are one namespace - rename this one, or declare it without export inside a module of your own`
+}
 function check_duplicate_decls() -> void {
   let k = new []pointer
   let v = new []Node
@@ -254,7 +263,7 @@ function check_duplicate_decls() -> void {
       if first != null {
         g_err_file = d.file
         g_err_line = d.line
-        perr(`'{d.s}' is defined twice (first in {first.file}:{itoa(first.line)})`)
+        perr(`'{d.s}' is defined twice (first in {first.file}:{itoa(first.line)}){dup_whose(first, d)}`)
       }
       ck_tab_put(k, v, key, d)
     }

tools/ludic-cli/test.ludic

@@ -1005,6 +1005,8 @@ function cmd_dev_test() -> int {
   reject_case("rejected/exported_kinds", "'Catch' is defined twice", "two modules that export one record still clash")
   reject_case("rejected/exported_events", "event 'Landed' is defined twice", "two modules that export one event clash")
   feat_case("modules/tangle", "", "4", "tangle.ludic (the program ludic deps is tested on)")
+  feat_case("modules/own_uiact", "", "3", "own_uiact.ludic (0.R4: a game's exported UiAct does not meet ludic.ui's, which is its own module's)")
+  reject_case("rejected/pkg_export_clash", "ludic_ui exports it, and exported names are one namespace", "a type named like a package's export says whose it is")
   reject_case("rejected/exported_twins", "function 'seed' is defined twice", "two modules that export one name still clash")
   feat_case("modules/layers", "", "5", "layers.ludic (L3: `module menu in layer app uses items` - one layer's modules use each other and may go round)")
   reject_case("rejected/layer_reach", "hud uses items.item_count", "a layered module is still held to its uses outside the layer")