[PATCH] Allow more lookup of types in dependent base classes

[Richard Smith]

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Comment at: lib/Sema/SemaDecl.cpp:139-141
@@ +138,5 @@
+  for (const auto &Base : RD->bases()) {
+    auto *TST = Base.getType()->getAs<TemplateSpecializationType>();
+    if (!TST)
+      continue;
+    auto *TD = TST->getTemplateName().getAsTemplateDecl();
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It'd be nice to also handle deriving from `A<T>::B`, and so on.

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Comment at: lib/Sema/SemaDecl.cpp:259-268
@@ -212,1 +258,12 @@
+    // For unqualified lookup in a class template in MSVC mode, look into
+    // dependent base classes where the primary class template is known.
+    if (Result.empty() && getLangOpts().MSVCCompat && (!SS || SS->isEmpty())) {
+      auto *RD = dyn_cast<CXXRecordDecl>(CurContext);
+      if (RD && RD->getDescribedClassTemplate()) {
+        ParsedType TypeInBase =
+            recoverFromTypeInKnownDependentBase(*this, RD, II, NameLoc);
+        if (TypeInBase)
+          return TypeInBase;
+      }
+    }
   }
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I suspect you'll also need to do something like this in `ClassifyName`.

================
Comment at: lib/Sema/SemaDecl.cpp:261-262
@@ +260,4 @@
+    if (Result.empty() && getLangOpts().MSVCCompat && (!SS || SS->isEmpty())) {
+      auto *RD = dyn_cast<CXXRecordDecl>(CurContext);
+      if (RD && RD->getDescribedClassTemplate()) {
+        ParsedType TypeInBase =
----------------
This seems rather specific. I suppose we don't need to worry much about function contexts, because we'll delay-parse most of those, but what about the cases where we don't (`auto` return type, `constexpr` functions) and nested classes of class templates? Is it feasible to walk upwards until we see a class template, if we're in a dependent context?

Also, what about a class template within another class template? Should we look in dependent base classes of both?

http://reviews.llvm.org/D4237