Handle use clauses in a separate package's spec.

ada/ast.py

@@ -23499,7 +23499,7 @@ class PackageBody(Body):
         # want to reference the envs that are "used" there.
         reference(Self.cast(AdaNode).singleton,
                   through=T.PackageBody.package_decl_uses_clauses_envs,
-                  cond=Not(Self.is_compilation_unit_root))
+                  cond=Not(Self.is_compilation_unit_root) | Self.is_subunit)
     )
 
     package_name = Field(type=T.DefiningName)

testsuite/tests/name_resolution/use_clause_separate_pkg/pkg-inner.adb

@@ -0,0 +1,9 @@
+separate(Pkg)
+package body Inner is
+   procedure Bar is
+      X : T;
+      pragma Test_Statement;
+   begin
+      null;
+   end Bar;
+end Inner;

testsuite/tests/name_resolution/use_clause_separate_pkg/pkg.adb

@@ -0,0 +1,17 @@
+package body Pkg is
+   package Types is
+      type T is null record;
+   end Types;
+
+   package Inner is
+      use Types;
+      procedure Bar;
+   end Inner;
+
+   procedure Test is
+   begin
+      Inner.Bar;
+   end Test;
+
+   package body Inner is separate;
+end Pkg;

testsuite/tests/name_resolution/use_clause_separate_pkg/pkg.ads

@@ -0,0 +1,3 @@
+package Pkg is
+   procedure Test;
+end Pkg;

testsuite/tests/name_resolution/use_clause_separate_pkg/test.out

@@ -0,0 +1,13 @@
+Analyzing pkg-inner.adb
+#######################
+
+Resolving xrefs for node <ObjectDecl ["X"] pkg-inner.adb:4:7-4:13>
+******************************************************************
+
+Expr: <Id "T" pkg-inner.adb:4:11-4:12>
+  references:    <DefiningName "T" pkg.adb:3:12-3:13>
+  type:          None
+  expected type: None
+
+
+Done.

testsuite/tests/name_resolution/use_clause_separate_pkg/test.yaml

@@ -0,0 +1,2 @@
+driver: name-resolution
+input_sources: [pkg-inner.adb]