Deprecate use of private variables from other modules

changelog/private.dd

@@ -0,0 +1,8 @@
+Deprecate the use of selectively imported private members
+
+$(LINK2 $(ROOT_DIR)spec/attribute.html#visibility_attributes, The specification states) that a private member
+is visible only from within the same module.
+Prior to this release, due to a bug, private members
+were visible through selective imports from other modules, violating the specification.
+Beginning with this release, accessing private members from outside the module
+in which they are declared will result in a deprecation message.

src/dmd/dsymbolsem.d

@@ -1148,9 +1148,18 @@ private extern(C++) final class DsymbolSemanticVisitor : Visitor
                 bool flag;
                 AliasDeclaration ad = imp.aliasdecls[i];
                 //printf("\tImport %s alias %s = %s, scope = %p\n", toPrettyChars(), aliases[i].toChars(), names[i].toChars(), ad._scope);
-                if (imp.mod.search(imp.loc, imp.names[i]) /*, IgnorePrivateImports*/)
+                Dsymbol sym = imp.mod.search(imp.loc, imp.names[i] /*, IgnorePrivateImports */);
+                if (sym)
                 {
                     flag = true;
+
+                    // Deprecated in 2018-01.
+                    // Change to error in 2019-01.
+                    // @@@DEPRECATED_2019-01@@@.
+                    import dmd.access : symbolIsVisible;
+                    if (!symbolIsVisible(sc, sym))
+                        imp.mod.deprecation(imp.loc, "member `%s` is not visible from module `%s`",
+                            imp.names[i].toChars(), sc._module.toChars());
                     ad.dsymbolSemantic(sc);
                     // If the import declaration is in non-root module,
                     // analysis of the aliased symbol is deferred.

test/fail_compilation/fail15896.d

@@ -0,0 +1,18 @@
+// PERMUTE_ARGS:
+// REQUIRED_ARGS: -de
+/*
+TEST_OUTPUT:
+---
+fail_compilation/fail15896.d(11): Deprecation: module `imports.imp15896` member `thebar` is not visible from module `fail15896`
+fail_compilation/fail15896.d(11): Deprecation: module `imports.imp15896` member `packagebar` is not visible from module `fail15896`
+---
+*/
+
+import imports.imp15896 : thebar, packagebar;
+
+int func()
+{
+    thebar +=1;
+    packagebar += 1;
+    return 0;
+}

test/fail_compilation/imports/imp15896.d

@@ -0,0 +1,4 @@
+module imports.imp15896;
+
+private int thebar=4;
+package int packagebar=3;