From: Douglas Gregor <dgregor@apple.com>
Date: Tue, 10 Apr 2012 19:03:30 +0000 (+0000)
Subject: Improve diagnostics in C++11 when a non-type template argument for a
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=50fadd19497f5fa6d8737786ba74af8354d28349;p=clang

Improve diagnostics in C++11 when a non-type template argument for a
non-type template parameter of pointer type is not a constant expression.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@154424 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 6994af855d..39bd5ac94e 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2344,6 +2344,8 @@ def err_template_arg_not_integral_or_enumeral : Error<
 def err_template_arg_not_ice : Error<
   "non-type template argument of type %0 is not an integral constant "
   "expression">;
+def err_template_arg_not_address_constant : Error<
+  "non-type template argument of type %0 is not a constant expression">;
 def err_template_arg_untyped_null_constant : Error<
   "null non-type template argument must be cast to template parameter type %0">;
 def err_template_arg_wrongtype_null_constant : Error<
@@ -2367,8 +2369,6 @@ def err_template_arg_no_ref_bind : Error<
 def err_template_arg_ref_bind_ignores_quals : Error<
   "reference binding of non-type template parameter of type %0 to template "
   "argument of type %1 ignores qualifiers">;
-def err_template_arg_not_address_constant : Error<
-  "non-type template argument of type %0 is not a constant expression">;
 def err_template_arg_not_decl_ref : Error<
   "non-type template argument does not refer to any declaration">;
 def err_template_arg_not_object_or_func_form : Error<
diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index a91304eed8..ff8c4dacc2 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -3479,10 +3479,35 @@ isNullPointerValueTemplateArgument(Sema &S, NonTypeTemplateParmDecl *Param,
     return NPV_NotNullPointer;
   
   // Determine whether we have a constant expression.
+  ExprResult ArgRV = S.DefaultFunctionArrayConversion(Arg);
+  if (ArgRV.isInvalid())
+    return NPV_Error;
+  Arg = ArgRV.take();
+  
   Expr::EvalResult EvalResult;
+  llvm::SmallVector<PartialDiagnosticAt, 8> Notes;
+  EvalResult.Diag = &Notes;
   if (!Arg->EvaluateAsRValue(EvalResult, S.Context) ||
-      EvalResult.HasSideEffects)
-    return NPV_NotNullPointer;
+      EvalResult.HasSideEffects) {
+    SourceLocation DiagLoc = Arg->getExprLoc();
+    
+    // If our only note is the usual "invalid subexpression" note, just point
+    // the caret at its location rather than producing an essentially
+    // redundant note.
+    if (Notes.size() == 1 && Notes[0].second.getDiagID() ==
+        diag::note_invalid_subexpr_in_const_expr) {
+      DiagLoc = Notes[0].first;
+      Notes.clear();
+    }
+    
+    S.Diag(DiagLoc, diag::err_template_arg_not_address_constant)
+      << Arg->getType() << Arg->getSourceRange();
+    for (unsigned I = 0, N = Notes.size(); I != N; ++I)
+      S.Diag(Notes[I].first, Notes[I].second);
+    
+    S.Diag(Param->getLocation(), diag::note_template_param_here);
+    return NPV_Error;
+  }
   
   // C++11 [temp.arg.nontype]p1:
   //   - an address constant expression of type std::nullptr_t
diff --git a/test/CXX/temp/temp.arg/temp.arg.nontype/p1-11.cpp b/test/CXX/temp/temp.arg/temp.arg.nontype/p1-11.cpp
index f31c3daf15..59ce8b68b7 100644
--- a/test/CXX/temp/temp.arg/temp.arg.nontype/p1-11.cpp
+++ b/test/CXX/temp/temp.arg/temp.arg.nontype/p1-11.cpp
@@ -12,7 +12,7 @@ constexpr std::nullptr_t get_nullptr() { return nullptr; }
 
 constexpr std::nullptr_t np = nullptr;
 
-std::nullptr_t nonconst_np;
+std::nullptr_t nonconst_np; // expected-note{{declared here}}
 
 IP<0> ip0; // expected-error{{null non-type template argument must be cast to template parameter type 'int *'}}
 IP<(0)> ip1; // expected-error{{null non-type template argument must be cast to template parameter type 'int *'}}
@@ -20,7 +20,8 @@ IP<nullptr> ip2;
 IP<get_nullptr()> ip3;
 IP<(int*)0> ip4;
 IP<np> ip5;
-IP<nonconst_np> ip5; // expected-error{{non-type template argument for template parameter of pointer type 'int *' must have its address taken}}
+IP<nonconst_np> ip5; // expected-error{{non-type template argument of type 'std::nullptr_t' (aka 'nullptr_t') is not a constant expression}} \
+// expected-note{{read of non-constexpr variable 'nonconst_np' is not allowed in a constant expression}}
 IP<(float*)0> ip6; // expected-error{{null non-type template argument of type 'float *' does not match template parameter of type 'int *'}}
 
 struct X { };