Revert r240335.

This failed to solve the problem it was aimed at, and introduced just as many
issues as it resolved. Realistically, we need to deal with the possibility that
multiple modules might define different internal linkage symbols with the same
name, and this isn't a problem unless two such symbols are simultaneously
visible.

The case where two modules define equivalent internal linkage symbols is
handled by r252063: if lookup finds multiple sufficiently-similar entities from
different modules, we just pick one of them as an extension (but we keep them
separate).

llvm-svn: 252957

clang/include/clang/Basic/LangOptions.def

@@ -133,7 +133,6 @@ COMPATIBLE_LANGOPT(ModulesStrictDeclUse, 1, 0, "require declaration of module us
 BENIGN_LANGOPT(ModulesErrorRecovery, 1, 1, "automatically import modules as needed when performing error recovery")
 BENIGN_LANGOPT(ImplicitModules, 1, 1, "build modules that are not specified via -fmodule-file")
 COMPATIBLE_LANGOPT(ModulesLocalVisibility, 1, 0, "local submodule visibility")
-COMPATIBLE_LANGOPT(ModulesHideInternalLinkage, 1, 1, "hiding non-visible internal linkage declarations from redeclaration lookup")
 COMPATIBLE_LANGOPT(Optimize          , 1, 0, "__OPTIMIZE__ predefined macro")
 COMPATIBLE_LANGOPT(OptimizeSize      , 1, 0, "__OPTIMIZE_SIZE__ predefined macro")
 LANGOPT(Static            , 1, 0, "__STATIC__ predefined macro (as opposed to __DYNAMIC__)")

clang/include/clang/Driver/CC1Options.td

@@ -388,10 +388,6 @@ def fmodules_local_submodule_visibility :
 def fmodule_format_EQ : Joined<["-"], "fmodule-format=">,
   HelpText<"Select the container format for clang modules and PCH. "
            "Supported options are 'raw' and 'obj'.">;
-def fno_modules_hide_internal_linkage :
-  Flag<["-"], "fno-modules-hide-internal-linkage">,
-  HelpText<"Make all declarations visible to redeclaration lookup, "
-           "even if they have internal linkage.">;
 def ftest_module_file_extension_EQ :
   Joined<["-"], "ftest-module-file-extension=">,
   HelpText<"introduce a module file extension for testing purposes. "

clang/include/clang/Sema/Sema.h

@@ -277,9 +277,7 @@ class Sema {
     // it will keep having external linkage. If it has internal linkage, we
     // will not link it. Since it has no previous decls, it will remain
     // with internal linkage.
-    if (getLangOpts().ModulesHideInternalLinkage)
-      return isVisible(Old) || New->isExternallyVisible();
-    return true;
+    return isVisible(Old) || New->isExternallyVisible();
   }
 
 public:

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1627,8 +1627,6 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
       Args.hasArg(OPT_fmodules_decluse) || Opts.ModulesStrictDeclUse;
   Opts.ModulesLocalVisibility =
       Args.hasArg(OPT_fmodules_local_submodule_visibility);
-  Opts.ModulesHideInternalLinkage =
-      !Args.hasArg(OPT_fno_modules_hide_internal_linkage);
   Opts.ModulesSearchAll = Opts.Modules &&
     !Args.hasArg(OPT_fno_modules_search_all) &&
     Args.hasArg(OPT_fmodules_search_all);

clang/lib/Sema/SemaDecl.cpp

@@ -4822,7 +4822,6 @@ NamedDecl *Sema::HandleDeclarator(Scope *S, Declarator &D,
   // If we're hiding internal-linkage symbols in modules from redeclaration
   // lookup, let name lookup know.
   if ((getLangOpts().Modules || getLangOpts().ModulesLocalVisibility) &&
-      getLangOpts().ModulesHideInternalLinkage &&
       D.getDeclSpec().getStorageClassSpec() != DeclSpec::SCS_typedef)
     Previous.setAllowHiddenInternal(false);
 

clang/test/Modules/submodules-merge-defs.cpp

@@ -3,7 +3,7 @@
 // RUN: %clang_cc1 -x c++ -std=c++11 -fmodules-cache-path=%t -fmodules -fimplicit-module-maps -I %S/Inputs/submodules-merge-defs %s -verify -fno-modules-error-recovery
 // RUN: %clang_cc1 -x c++ -std=c++11 -fmodules-cache-path=%t -fmodules -fimplicit-module-maps -I %S/Inputs/submodules-merge-defs %s -verify -fno-modules-error-recovery -fmodules-local-submodule-visibility -DTEXTUAL
 // RUN: %clang_cc1 -x c++ -std=c++11 -fmodules-cache-path=%t -fmodules -fimplicit-module-maps -I %S/Inputs/submodules-merge-defs %s -verify -fno-modules-error-recovery -fmodules-local-submodule-visibility
-// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules-cache-path=%t -fimplicit-module-maps -I %S/Inputs/submodules-merge-defs %s -verify -fno-modules-error-recovery -fmodules-local-submodule-visibility -DTEXTUAL -DEARLY_INDIRECT_INCLUDE -fno-modules-hide-internal-linkage
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules-cache-path=%t -fimplicit-module-maps -I %S/Inputs/submodules-merge-defs %s -verify -fno-modules-error-recovery -fmodules-local-submodule-visibility -DTEXTUAL -DEARLY_INDIRECT_INCLUDE
 // RUN: %clang_cc1 -x c++ -std=c++11 -fmodules-cache-path=%t -fmodules -fimplicit-module-maps -I %S/Inputs/submodules-merge-defs %s -verify -fno-modules-error-recovery -fmodules-local-submodule-visibility -fmodule-feature use_defs_twice -DIMPORT_USE_2
 
 // Trigger import of definitions, but don't make them visible.
@@ -111,4 +111,9 @@ MergeFunctionTemplateSpecializations::X<int>::Q<char> xiqc;
 #ifdef TEXTUAL
 #include "use-defs.h"
 void use_static_inline() { StaticInline::g({}); }
+#ifdef EARLY_INDIRECT_INCLUDE
+// expected-warning@-2 {{ambiguous use of internal linkage declaration 'g' defined in multiple modules}}
+// expected-note@defs.h:71 {{declared here in module 'redef'}}
+// expected-note@defs.h:71 {{declared here in module 'stuff.use'}}
+#endif
 #endif

clang/test/Modules/using-decl.cpp

@@ -1,8 +1,6 @@
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -x objective-c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs %s -verify -DEARLY_IMPORT
 // RUN: %clang_cc1 -x objective-c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs %s -verify -UEARLY_IMPORT
-// RUN: %clang_cc1 -x objective-c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs %s -verify -DEARLY_IMPORT -fno-modules-hide-internal-linkage
-// RUN: %clang_cc1 -x objective-c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs %s -verify -UEARLY_IMPORT -fno-modules-hide-internal-linkage
 // RUN: %clang_cc1 -x objective-c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs %s -verify -DEARLY_IMPORT -fmodules-local-submodule-visibility
 // RUN: %clang_cc1 -x objective-c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs %s -verify -UEARLY_IMPORT -fmodules-local-submodule-visibility