Fix PR12378: provide conversion warnings on default args of function templates

Apparently we weren't checking default arguments when they were instantiated.
This adds the check, fixes the lack of instantiation caching (which seems like
it was mostly implemented but just missed the last step), and avoids
implementing non-dependent default args (for non-dependent parameter types) as
uninstantiated default arguments (so that we don't warn once for every
instantiation when it's not instantiation dependent).

Reviewed by Richard Smith.

llvm-svn: 155838

3 files changed, 30 insertions, 4 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 87a67ff632b..4ed588565f1 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -3300,9 +3300,11 @@ ExprResult Sema::BuildCXXDefaultArgExpr(SourceLocation CallLoc,
     if (Result.isInvalid())
       return ExprError();
 
+    Expr *Arg = Result.takeAs<Expr>();
+    CheckImplicitConversions(Arg, Arg->getExprLoc());
+    Param->setDefaultArg(Arg);
     // Build the default argument expression.
-    return Owned(CXXDefaultArgExpr::Create(Context, CallLoc, Param,
-                                           Result.takeAs<Expr>()));
+    return Owned(CXXDefaultArgExpr::Create(Context, CallLoc, Param, Arg));
   }
 
   // If the default expression creates temporaries, we need to
diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 793ee0e50ad..3635e64f3d0 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1594,8 +1594,13 @@ ParmVarDecl *Sema::SubstParmVarDecl(ParmVarDecl *OldParm,
   } else if (OldParm->hasUnparsedDefaultArg()) {
     NewParm->setUnparsedDefaultArg();
     UnparsedDefaultArgInstantiations[OldParm].push_back(NewParm);
-  } else if (Expr *Arg = OldParm->getDefaultArg())
-    NewParm->setUninstantiatedDefaultArg(Arg);
+  } else if (Expr *Arg = OldParm->getDefaultArg()) {
+    if (Arg->isInstantiationDependent() ||
+        OldDI->getType()->isInstantiationDependentType())
+      NewParm->setUninstantiatedDefaultArg(Arg);
+    else
+      NewParm->setDefaultArg(Arg);
+  }
 
   NewParm->setHasInheritedDefaultArg(OldParm->hasInheritedDefaultArg());
   
diff --git a/clang/test/SemaCXX/conversion.cpp b/clang/test/SemaCXX/conversion.cpp
index a64b18721a5..225bc837b56 100644
--- a/clang/test/SemaCXX/conversion.cpp
+++ b/clang/test/SemaCXX/conversion.cpp
@@ -81,3 +81,22 @@ void test3() {
 #define FINIT int a3 = NULL;
   FINIT // expected-warning {{implicit conversion of NULL constant to 'int'}}
 }
+
+namespace test4 {
+  template<typename T>
+  void tmpl(char c = NULL, // expected-warning {{implicit conversion of NULL constant to 'char'}}
+            T a = NULL, // expected-warning {{implicit conversion of NULL constant to 'char'}} \
+                           expected-warning {{implicit conversion of NULL constant to 'int'}}
+            T b = 1024) { // expected-warning {{implicit conversion from 'int' to 'char' changes value from 1024 to 0}}
+  }
+
+  template<typename T>
+  void tmpl2(T t = NULL) {
+  }
+
+  void func() {
+    tmpl<char>(); // expected-note {{in instantiation of default function argument expression for 'tmpl<char>' required here}}
+    tmpl<int>(); // expected-note {{in instantiation of default function argument expression for 'tmpl<int>' required here}}
+    tmpl2<int*>();
+  }
+}