Sema: make check for namespace lookup of private declarations more strict

Previously sema only checked that the private declaration was in the same
file as the lookup but now it also checks that the namespace where
the decl was included from was also in the same file.

Closes #13077

src/Sema.zig

@@ -5658,14 +5658,14 @@ fn lookupInNamespace(
         const src_file = block.namespace.file_scope;
 
         const gpa = sema.gpa;
-        var checked_namespaces: std.AutoArrayHashMapUnmanaged(*Namespace, void) = .{};
+        var checked_namespaces: std.AutoArrayHashMapUnmanaged(*Namespace, bool) = .{};
         defer checked_namespaces.deinit(gpa);
 
         // Keep track of name conflicts for error notes.
         var candidates: std.ArrayListUnmanaged(Decl.Index) = .{};
         defer candidates.deinit(gpa);
 
-        try checked_namespaces.put(gpa, namespace, {});
+        try checked_namespaces.put(gpa, namespace, namespace.file_scope == src_file);
         var check_i: usize = 0;
 
         while (check_i < checked_namespaces.count()) : (check_i += 1) {
@@ -5674,7 +5674,7 @@ fn lookupInNamespace(
                 // Skip decls which are not marked pub, which are in a different
                 // file than the `a.b`/`@hasDecl` syntax.
                 const decl = mod.declPtr(decl_index);
-                if (decl.is_pub or src_file == decl.getFileScope()) {
+                if (decl.is_pub or (src_file == decl.getFileScope() and checked_namespaces.values()[check_i])) {
                     try candidates.append(gpa, decl_index);
                 }
             }
@@ -5693,7 +5693,7 @@ fn lookupInNamespace(
                 try sema.ensureDeclAnalyzed(sub_usingnamespace_decl_index);
                 const ns_ty = sub_usingnamespace_decl.val.castTag(.ty).?.data;
                 const sub_ns = ns_ty.getNamespace().?;
-                try checked_namespaces.put(gpa, sub_ns, {});
+                try checked_namespaces.put(gpa, sub_ns, src_file == sub_usingnamespace_decl.getFileScope());
             }
         }
 

test/behavior/usingnamespace.zig

@@ -75,3 +75,7 @@ test {
     const a = AA.b(42);
     try expect(a.x == AA.c().expected);
 }
+
+comptime {
+    _ = @import("usingnamespace/file_1.zig");
+}

test/behavior/usingnamespace/file_0.zig

@@ -0,0 +1 @@
+pub const A = 123;

test/behavior/usingnamespace/file_1.zig

@@ -0,0 +1,9 @@
+const std = @import("std");
+const expect = std.testing.expect;
+const imports = @import("imports.zig");
+
+const A = 456;
+
+test {
+    try expect(imports.A == 123);
+}

test/behavior/usingnamespace/imports.zig

@@ -0,0 +1,5 @@
+const file_0 = @import("file_0.zig");
+const file_1 = @import("file_1.zig");
+
+pub usingnamespace file_0;
+pub usingnamespace file_1;