[Modules][ObjC] Warn on the use of '@import' in framework headers

Using @import in framework headers inhibit the use of such headers
when not using modules, this is specially bad for headers that end
up in the SDK (or any other system framework). Add a warning to give
users some indication that this is discouraged.

rdar://problem/39192894

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@335780 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/DiagnosticGroups.td

@@ -34,6 +34,7 @@ def AutoImport : DiagGroup<"auto-import">;
 def FrameworkHdrQuotedInclude : DiagGroup<"quoted-include-in-framework-header">;
 def FrameworkIncludePrivateFromPublic :
   DiagGroup<"framework-include-private-from-public">;
+def FrameworkHdrAtImport : DiagGroup<"atimport-in-framework-header">;
 def CXX14BinaryLiteral : DiagGroup<"c++14-binary-literal">;
 def CXXPre14CompatBinaryLiteral : DiagGroup<"c++98-c++11-compat-binary-literal">;
 def GNUBinaryLiteral : DiagGroup<"gnu-binary-literal">;

include/clang/Basic/DiagnosticParseKinds.td

@@ -248,6 +248,11 @@ def err_unexpected_at : Error<"unexpected '@' in program">;
 def err_atimport : Error<
 "use of '@import' when modules are disabled">;
 
+def warn_atimport_in_framework_header : Warning<
+  "use of '@import' in framework header is discouraged, "
+  "including this header requires -fmodules">,
+  InGroup<FrameworkHdrAtImport>;
+
 def err_invalid_reference_qualifier_application : Error<
   "'%0' qualifier may not be applied to a reference">;
 def err_illegal_decl_reference_to_reference : Error<

lib/Parse/Parser.cpp

@@ -20,6 +20,7 @@
 #include "clang/Sema/DeclSpec.h"
 #include "clang/Sema/ParsedTemplate.h"
 #include "clang/Sema/Scope.h"
+#include "llvm/Support/Path.h"
 using namespace clang;
 
 
@@ -2123,6 +2124,7 @@ Decl *Parser::ParseModuleImport(SourceLocation AtLoc) {
   assert((AtLoc.isInvalid() ? Tok.is(tok::kw_import)
                             : Tok.isObjCAtKeyword(tok::objc_import)) &&
          "Improper start to module import");
+  bool IsObjCAtImport = Tok.isObjCAtKeyword(tok::objc_import);
   SourceLocation ImportLoc = ConsumeToken();
   SourceLocation StartLoc = AtLoc.isInvalid() ? ImportLoc : AtLoc;
   
@@ -2146,6 +2148,16 @@ Decl *Parser::ParseModuleImport(SourceLocation AtLoc) {
   if (Import.isInvalid())
     return nullptr;
 
+  // Using '@import' in framework headers requires modules to be enabled so that
+  // the header is parseable. Emit a warning to make the user aware.
+  if (IsObjCAtImport && AtLoc.isValid()) {
+    auto &SrcMgr = PP.getSourceManager();
+    auto *FE = SrcMgr.getFileEntryForID(SrcMgr.getFileID(AtLoc));
+    if (FE && llvm::sys::path::parent_path(FE->getDir()->getName())
+                  .endswith(".framework"))
+      Diags.Report(AtLoc, diag::warn_atimport_in_framework_header);
+  }
+
   return Import.get();
 }
 

test/Modules/Inputs/at-import-in-framework-header/A.framework/Headers/A.h

@@ -0,0 +1,2 @@
+@import B;
+int foo();

test/Modules/Inputs/at-import-in-framework-header/A.framework/Modules/module.modulemap

@@ -0,0 +1,4 @@
+// at-import-in-framework-header/A.framework/Modules/module.modulemap
+framework module A {
+  header "A.h"
+}

test/Modules/Inputs/at-import-in-framework-header/module.modulemap

@@ -0,0 +1,2 @@
+// at-import-in-framework-header/module.modulemap
+module B {}

test/Modules/at-import-in-framework-header.m

@@ -0,0 +1,17 @@
+// REQUIRES: shell
+
+// RUN: rm -rf %t
+// RUN: mkdir %t
+
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache \
+// RUN:   -F%S/Inputs/at-import-in-framework-header -I%S/Inputs/at-import-in-framework-header \
+// RUN:   -Watimport-in-framework-header -fsyntax-only %s \
+// RUN:   2>%t/stderr
+// RUN: FileCheck --input-file=%t/stderr %s
+
+// CHECK: use of '@import' in framework header is discouraged
+
+#import <A/A.h>
+
+int bar() { return foo(); }
+

test/VFS/umbrella-mismatch.m

@@ -1,7 +1,7 @@
 // RUN: rm -rf %t
 // RUN: sed -e "s;INPUT_DIR;%/S/Inputs;g" -e "s;OUT_DIR;%/S/Inputs;g" %S/Inputs/vfsoverlay.yaml > %t.yaml
 
-// RUN: %clang_cc1 -Werror -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -ivfsoverlay %t.yaml -F %S/Inputs -fsyntax-only %s -verify
-// RUN: %clang_cc1 -Werror -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -F %S/Inputs -fsyntax-only %s -verify
+// RUN: %clang_cc1 -Werror -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -ivfsoverlay %t.yaml -F %S/Inputs -fsyntax-only %s -Wno-atimport-in-framework-header -verify
+// RUN: %clang_cc1 -Werror -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -F %S/Inputs -fsyntax-only %s -Wno-atimport-in-framework-header -verify
 // expected-no-diagnostics
 @import UsesFoo;