[Modules] Allow modules specified by -fmodule-map-file to shadow implicitly found ones

When modules come from module map files explicitly specified by
-fmodule-map-file= arguments, allow those to override/shadow modules
with the same name that are found implicitly by header search. If such a
module is looked up by name (e.g. @import), we will always find the one
from -fmodule-map-file. If we try to use a shadowed module by including
one of its headers report an error.

This enables developers to force use of a specific copy of their module
to be used if there are multiple copies that would otherwise be visible,
for example if they develop modules that are installed in the default
search paths.

Patch originally by Ben Langmuir,
http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20151116/143425.html

Based on cfe-dev discussion:
http://lists.llvm.org/pipermail/cfe-dev/2015-November/046164.html

Differential Revision: https://reviews.llvm.org/D31269

rdar://problem/23612102

llvm-svn: 321781

1 files changed, 68 insertions, 32 deletions

diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
index b3ac10c5c5a..c2ea64fcd12 100644
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -744,14 +744,13 @@ Module *ModuleMap::lookupModuleQualified(StringRef Name, Module *Context) const{
   return Context->findSubmodule(Name);
 }
 
-std::pair<Module *, bool> ModuleMap::findOrCreateModule(StringRef Name,
-                                                        Module *Parent,
-                                                        bool IsFramework,
-                                                        bool IsExplicit) {
+std::pair<Module *, bool>
+ModuleMap::findOrCreateModule(StringRef Name, Module *Parent, bool IsFramework,
+                              bool IsExplicit, bool UsesExplicitModuleMapFile) {
   // Try to find an existing module with this name.
   if (Module *Sub = lookupModuleQualified(Name, Parent))
     return std::make_pair(Sub, false);
-  
+
   // Create a new module with this name.
   Module *Result = new Module(Name, SourceLocation(), Parent, IsFramework,
                               IsExplicit, NumCreatedModules++);
@@ -759,6 +758,8 @@ std::pair<Module *, bool> ModuleMap::findOrCreateModule(StringRef Name,
     if (LangOpts.CurrentModule == Name)
       SourceModule = Result;
     Modules[Name] = Result;
+    if (UsesExplicitModuleMapFile)
+      ExplicitlyProvidedModules.insert(Result);
   }
   return std::make_pair(Result, true);
 }
@@ -999,6 +1000,19 @@ Module *ModuleMap::inferFrameworkModule(const DirectoryEntry *FrameworkDir,
   return Result;
 }
 
+Module *ModuleMap::createShadowedModule(StringRef Name, bool IsFramework,
+                                        Module *ShadowingModule) {
+
+  // Create a new module with this name.
+  Module *Result =
+      new Module(Name, SourceLocation(), /*Parent=*/nullptr, IsFramework,
+                 /*IsExplicit=*/false, NumCreatedModules++);
+  Result->ShadowingModule = ShadowingModule;
+  Result->IsAvailable = false;
+
+  return Result;
+}
+
 void ModuleMap::setUmbrellaHeader(Module *Mod, const FileEntry *UmbrellaHeader,
                                   Twine NameAsWritten) {
   Headers[UmbrellaHeader].push_back(KnownHeader(Mod, NormalHeader));
@@ -1116,6 +1130,11 @@ void ModuleMap::excludeHeader(Module *Mod, Module::Header Header) {
   Mod->Headers[Module::HK_Excluded].push_back(std::move(Header));
 }
 
+void ModuleMap::setExplicitlyProvided(Module *Mod) {
+  assert(Modules[Mod->Name] == Mod && "explicitly provided module is shadowed");
+  ExplicitlyProvidedModules.insert(Mod);
+}
+
 const FileEntry *
 ModuleMap::getContainingModuleMapFile(const Module *Module) const {
   if (Module->DefinitionLoc.isInvalid())
@@ -1319,7 +1338,9 @@ namespace clang {
 
     /// \brief Consume the current token and return its location.
     SourceLocation consumeToken();
-    
+
+    bool UsesExplicitModuleMapFile = false;
+
     /// \brief Skip tokens until we reach the a token with the given kind
     /// (or the end of the file).
     void skipUntil(MMToken::TokenKind K);
@@ -1345,20 +1366,19 @@ namespace clang {
     bool parseOptionalAttributes(Attributes &Attrs);
     
   public:
-    explicit ModuleMapParser(Lexer &L, SourceManager &SourceMgr, 
-                             const TargetInfo *Target,
-                             DiagnosticsEngine &Diags,
-                             ModuleMap &Map,
-                             const FileEntry *ModuleMapFile,
-                             const DirectoryEntry *Directory,
-                             bool IsSystem)
+    explicit ModuleMapParser(Lexer &L, SourceManager &SourceMgr,
+                             const TargetInfo *Target, DiagnosticsEngine &Diags,
+                             ModuleMap &Map, const FileEntry *ModuleMapFile,
+                             const DirectoryEntry *Directory, bool IsSystem,
+                             bool UsesExplicitModuleMapFile)
         : L(L), SourceMgr(SourceMgr), Target(Target), Diags(Diags), Map(Map),
           ModuleMapFile(ModuleMapFile), Directory(Directory),
-          IsSystem(IsSystem) {
+          IsSystem(IsSystem),
+          UsesExplicitModuleMapFile(UsesExplicitModuleMapFile) {
       Tok.clear();
       consumeToken();
     }
-    
+
     bool parseModuleMapFile();
 
     bool terminatedByDirective() { return false; }
@@ -1787,6 +1807,7 @@ void ModuleMapParser::parseModuleDecl() {
   SourceLocation LBraceLoc = consumeToken();
   
   // Determine whether this (sub)module has already been defined.
+  Module *ShadowingModule = nullptr;
   if (Module *Existing = Map.lookupModuleQualified(ModuleName, ActiveModule)) {
     // We might see a (re)definition of a module that we already have a
     // definition for in two cases:
@@ -1812,23 +1833,36 @@ void ModuleMapParser::parseModuleDecl() {
       }
       return;
     }
-    
-    Diags.Report(ModuleNameLoc, diag::err_mmap_module_redefinition)
-      << ModuleName;
-    Diags.Report(Existing->DefinitionLoc, diag::note_mmap_prev_definition);
-    
-    // Skip the module definition.
-    skipUntil(MMToken::RBrace);
-    if (Tok.is(MMToken::RBrace))
-      consumeToken();
-    
-    HadError = true;
-    return;
+
+    if (!Existing->Parent &&
+        Map.mayShadowModuleBeingParsed(Existing, UsesExplicitModuleMapFile)) {
+      ShadowingModule = Existing;
+    } else {
+      // This is not a shawdowed module decl, it is an illegal redefinition.
+      Diags.Report(ModuleNameLoc, diag::err_mmap_module_redefinition)
+          << ModuleName;
+      Diags.Report(Existing->DefinitionLoc, diag::note_mmap_prev_definition);
+
+      // Skip the module definition.
+      skipUntil(MMToken::RBrace);
+      if (Tok.is(MMToken::RBrace))
+        consumeToken();
+
+      HadError = true;
+      return;
+    }
   }
 
   // Start defining this module.
-  ActiveModule = Map.findOrCreateModule(ModuleName, ActiveModule, Framework,
-                                        Explicit).first;
+  if (ShadowingModule) {
+    ActiveModule =
+        Map.createShadowedModule(ModuleName, Framework, ShadowingModule);
+  } else {
+    ActiveModule = Map.findOrCreateModule(ModuleName, ActiveModule, Framework,
+                                          Explicit, UsesExplicitModuleMapFile)
+                       .first;
+  }
+
   ActiveModule->DefinitionLoc = ModuleNameLoc;
   if (Attrs.IsSystem || IsSystem)
     ActiveModule->IsSystem = true;
@@ -2004,7 +2038,7 @@ void ModuleMapParser::parseExternModuleDecl() {
         Map.HeaderInfo.getHeaderSearchOpts().ModuleMapFileHomeIsCwd
             ? Directory
             : File->getDir(),
-        FileID(), nullptr, ExternLoc);
+        false /*IsExplicitlyProvided*/, FileID(), nullptr, ExternLoc);
 }
 
 /// Whether to add the requirement \p Feature to the module \p M.
@@ -2811,7 +2845,8 @@ bool ModuleMapParser::parseModuleMapFile() {
 }
 
 bool ModuleMap::parseModuleMapFile(const FileEntry *File, bool IsSystem,
-                                   const DirectoryEntry *Dir, FileID ID,
+                                   const DirectoryEntry *Dir,
+                                   bool IsExplicitlyProvided, FileID ID,
                                    unsigned *Offset,
                                    SourceLocation ExternModuleLoc) {
   assert(Target && "Missing target information");
@@ -2841,7 +2876,7 @@ bool ModuleMap::parseModuleMapFile(const FileEntry *File, bool IsSystem,
           Buffer->getBufferEnd());
   SourceLocation Start = L.getSourceLocation();
   ModuleMapParser Parser(L, SourceMgr, Target, Diags, *this, File, Dir,
-                         IsSystem);
+                         IsSystem, IsExplicitlyProvided);
   bool Result = Parser.parseModuleMapFile();
   ParsedModuleMap[File] = Result;
 
@@ -2854,5 +2889,6 @@ bool ModuleMap::parseModuleMapFile(const FileEntry *File, bool IsSystem,
   // Notify callbacks that we parsed it.
   for (const auto &Cb : Callbacks)
     Cb->moduleMapFileRead(Start, *File, IsSystem);
+
   return Result;
 }