[Frontend] Avoid storing StringRef values in ModuleAliasMap

Previously we would insert StringRefs that reference the keys in the
map, but that breaks if the invocation ever gets copied. Switch to
`std::string`.

rdar://148130166

Author: hamishknight

include/swift/AST/ASTContext.h

@@ -620,7 +620,7 @@ class ASTContext final {
   /// For example, if '-module-alias Foo=X -module-alias Bar=Y' input is passed in, the aliases Foo and Bar are
   /// the names of the imported or referenced modules in source files in the main module, and X and Y
   /// are the real (physical) module names on disk.
-  void setModuleAliases(const llvm::StringMap<StringRef> &aliasMap);
+  void setModuleAliases(const llvm::StringMap<std::string> &aliasMap);
 
   /// Adds a given alias to the map of Identifiers between module aliases and
   /// their actual names.

include/swift/Frontend/FrontendOptions.h

@@ -58,7 +58,7 @@ class FrontendOptions {
   std::string ImplicitObjCPCHPath;
 
   /// The map of aliases and real names of imported or referenced modules.
-  llvm::StringMap<StringRef> ModuleAliasMap;
+  llvm::StringMap<std::string> ModuleAliasMap;
 
   /// The name of the module that the frontend is building.
   std::string ModuleName;

lib/AST/ASTContext.cpp

@@ -2151,15 +2151,14 @@ void ASTContext::addModuleInterfaceChecker(
   getImpl().InterfaceChecker = std::move(checker);
 }
 
-void ASTContext::setModuleAliases(const llvm::StringMap<StringRef> &aliasMap) {
+void ASTContext::setModuleAliases(
+    const llvm::StringMap<std::string> &aliasMap) {
   // This setter should be called only once after ASTContext has been initialized
   assert(ModuleAliasMap.empty());
-  
-  for (auto k: aliasMap.keys()) {
-    auto v = aliasMap.lookup(k);
-    if (!v.empty()) {
-      addModuleAlias(k, v);
-    }
+
+  for (auto &entry : aliasMap) {
+    if (!entry.getValue().empty())
+      addModuleAlias(entry.getKey(), entry.getValue());
   }
 }
 

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -980,13 +980,12 @@ bool ModuleAliasesConverter::computeModuleAliases(std::vector<std::string> args,
 
       // First, add the real name as a key to prevent it from being
       // used as an alias
-      if (!options.ModuleAliasMap.insert({rhs, StringRef()}).second) {
+      if (!options.ModuleAliasMap.insert({rhs, ""}).second) {
         diags.diagnose(SourceLoc(), diag::error_module_alias_duplicate, rhs);
         return false;
       }
       // Next, add the alias as a key and the real name as a value to the map
-      auto underlyingName = options.ModuleAliasMap.find(rhs)->first();
-      if (!options.ModuleAliasMap.insert({lhs, underlyingName}).second) {
+      if (!options.ModuleAliasMap.insert({lhs, rhs.str()}).second) {
         diags.diagnose(SourceLoc(), diag::error_module_alias_duplicate, lhs);
         return false;
       }

test/SourceKit/Misc/rdar148130166.swift

@@ -0,0 +1,5 @@
+// RUN: env DYLD_INSERT_LIBRARIES=/usr/lib/libgmalloc.dylib %sourcekitd-test -req=active-regions %s -- %s -module-name B -module-alias A=B
+// Make sure we don't crash.
+
+// guardmalloc is incompatible with ASAN
+// REQUIRES: no_asan