Diagnose self-imports of the module being compiled.

The case where this comes up is when people name their app and framework
targets the same thing, or when they've renamed their test target module
in an attempt to avoid issues with  NSClassFromString and differing
runtime names. We currently do various wrong things when this happens,
so just emit an error instead.

I left a hole for our overlays, which use '@exported import <the-current-module>'
to get at their Clang modules. The previous commit means this can be
replaced by -import-underlying-module, but that doesn't help our tests,
which use -enable-source-import for their overlays. Which we should stop doing.

rdar://problem/21254367

Swift SVN r29440

Author: jrose-apple

include/swift/AST/DiagnosticsSema.def

@@ -182,6 +182,8 @@ NOTE(sema_no_import_no_sdk,sema_nb,none,
 NOTE(sema_no_import_no_sdk_xcrun,sema_nb,none,
      "use \"xcrun -sdk macosx swift\" to select the default OS X SDK installed "
      "with Xcode", ())
+ERROR(sema_import_current_module,sema_nb,none,
+      "cannot import module being compiled", ())
 ERROR(sema_opening_import,sema_nb,Fatal,
       "opening import file for module %0: %1", (Identifier, StringRef))
 

lib/Sema/NameBinding.cpp

@@ -76,7 +76,11 @@ NameBinder::getModule(ArrayRef<std::pair<Identifier, SourceLoc>> modulePath) {
   // If the imported module name is the same as the current module,
   // skip the Swift module loader and use the Clang module loader instead.
   // This allows a Swift module to extend a Clang module of the same name.
-  if (moduleID.first == SF.getParentModule()->getName() && modulePath.size() == 1) {
+  //
+  // FIXME: We'd like to only use this in SIL mode, but unfortunately we use it
+  // for our fake overlays as well.
+  if (moduleID.first == SF.getParentModule()->getName() &&
+      modulePath.size() == 1) {
     if (auto importer = Context.getClangModuleLoader())
       return importer->loadModule(moduleID.second, modulePath);
     return nullptr;
@@ -130,9 +134,27 @@ static const char *getImportKindString(ImportKind kind) {
   }
 }
 
+static bool shouldImportSelfImportClang(const ImportDecl *ID,
+                                        const SourceFile &SF) {
+  // FIXME: We use '@exported' for fake overlays in testing.
+  if (ID->isExported())
+    return true;
+  if (SF.Kind == SourceFileKind::SIL)
+    return true;
+  return false;
+}
+
 void NameBinder::addImport(
     SmallVectorImpl<std::pair<ImportedModule, ImportOptions>> &imports,
     ImportDecl *ID) {
+  if (ID->getModulePath().front().first == SF.getParentModule()->getName() &&
+      ID->getModulePath().size() == 1 && !shouldImportSelfImportClang(ID, SF)) {
+    // If the imported module name is the same as the current module,
+    // produce an error.
+    Context.Diags.diagnose(ID, diag::sema_import_current_module);
+    return;
+  }
+
   Module *M = getModule(ID->getModulePath());
   if (!M) {
     SmallString<64> modulePathStr;

stdlib/public/SDK/Foundation/NSError.swift

@@ -1,4 +1,3 @@
-import Foundation
 import CoreFoundation
 import Darwin
 

stdlib/public/SDK/simd/simd.swift.gyb

@@ -13,7 +13,6 @@
 //===----------------------------------------------------------------------===//
 
 import Darwin
-import simd
 
 % component = ['x','y','z','w']
 % scalar_types = ['Float','Double','Int32']

test/ClangModules/nullability.swift

@@ -1,8 +1,7 @@
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -parse -I %S/Inputs/custom-modules %s -verify
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -parse -I %S/Inputs/custom-modules %s -import-underlying-module -verify
 
 // REQUIRES: objc_interop
 
-import nullability;
 import CoreCooling
 
 func testSomeClass(sc: SomeClass, osc: SomeClass?) {

test/ClangModules/script.swift

@@ -1,5 +1,4 @@
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -parse -verify -I %S/Inputs/custom-modules %s
-
-import script // Clang module
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -parse -verify -I %S/Inputs/custom-modules %s -import-underlying-module
 
 var _ : ScriptTy
+print()

test/decl/import/import.swift

@@ -3,7 +3,7 @@
 // RUN: echo "public struct X {}; public var x = X()" | %target-swift-frontend -module-name import_builtin -parse-stdlib -emit-module -o %t -
 // RUN: echo "public func foo() -> Int { return false }" > %t/import_text.swift
 // RUN: echo "public func pho$(printf '\xC3\xBB')x() -> Int { return false }" > %t/fran$(printf '\xC3\xA7')ais.swift
-// RUN: %target-swift-frontend -parse %s -I %t -sdk "" -enable-source-import -verify -show-diagnostics-after-fatal
+// RUN: %target-swift-frontend -parse %s -I %t -sdk "" -enable-source-import -module-name main -verify -show-diagnostics-after-fatal
 
 import Builtin  // expected-error {{no such module 'Builtin'}}
 
@@ -55,3 +55,5 @@ var _ : Int = foo()
 
 import français
 import func français.phoûx
+
+import main // expected-error {{cannot import module being compiled}}