[PATCH] D55552: [Sema] Better static assert diagnostics for expressions involving temporaries.

[Clement Courbet via Phabricator via cfe-commits]

courbet created this revision.
courbet added reviewers: aaron.ballman, Quuxplusone.
Herald added a subscriber: cfe-commits.

Handles expressions such as:

- `std::is_const<T>()`
- `std::is_const<T>()()`;
- `std::is_same(decltype(U()), V>::value`;


Repository:
  rC Clang

https://reviews.llvm.org/D55552

Files:
  lib/Sema/SemaTemplate.cpp
  test/SemaCXX/static-assert.cpp


Index: test/SemaCXX/static-assert.cpp
===================================================================
--- test/SemaCXX/static-assert.cpp
+++ test/SemaCXX/static-assert.cpp
@@ -76,6 +76,8 @@
   static const Tp value = v;
   typedef Tp value_type;
   typedef integral_constant type;
+  constexpr operator value_type() const noexcept { return value; }
+  constexpr value_type operator()() const noexcept { return value; }
 };
 
 template <class Tp, Tp v>
@@ -103,6 +105,7 @@
 } // namespace std
 
 struct ExampleTypes {
+  explicit ExampleTypes(int);
   using T = int;
   using U = float;
 };
@@ -119,6 +122,18 @@
 // expected-error@-1{{static_assert failed due to requirement 'std::is_const<const int>::value == false' "message"}}
 static_assert(!(std::is_const<const ExampleTypes::T>::value == true), "message");
 // expected-error@-1{{static_assert failed due to requirement '!(std::is_const<const int>::value == true)' "message"}}
+static_assert(std::is_const<ExampleTypes::T>(), "message");
+// expected-error@-1{{static_assert failed due to requirement 'std::is_const<int>()' "message"}}
+static_assert(!(std::is_const<const ExampleTypes::T>()()), "message");
+// expected-error@-1{{static_assert failed due to requirement '!(std::is_const<const int>()())' "message"}}
+static_assert(std::is_same<decltype(std::is_const<const ExampleTypes::T>()), int>::value, "message");
+// expected-error@-1{{static_assert failed due to requirement 'std::is_same<std::is_const<const int>, int>::value' "message"}}
+static_assert(std::is_const<decltype(ExampleTypes::T(3))>::value, "message");
+// expected-error@-1{{static_assert failed due to requirement 'std::is_const<int>::value' "message"}}
+static_assert(std::is_const<decltype(ExampleTypes::T())>::value, "message");
+// expected-error@-1{{static_assert failed due to requirement 'std::is_const<int>::value' "message"}}
+static_assert(std::is_const<decltype(ExampleTypes(3))>::value, "message");
+// expected-error@-1{{static_assert failed due to requirement 'std::is_const<ExampleTypes>::value' "message"}}
 
 struct BI_tag {};
 struct RAI_tag : BI_tag {};
Index: lib/Sema/SemaTemplate.cpp
===================================================================
--- lib/Sema/SemaTemplate.cpp
+++ lib/Sema/SemaTemplate.cpp
@@ -3059,8 +3059,9 @@
 // for actual types.
 class FailedBooleanConditionPrinterHelper : public PrinterHelper {
 public:
-  explicit FailedBooleanConditionPrinterHelper(const PrintingPolicy &P)
-      : Policy(P) {}
+  FailedBooleanConditionPrinterHelper(const ASTContext &Context,
+                                      const PrintingPolicy &P)
+      : Context(Context), Policy(P) {}
 
   bool handledStmt(Stmt *E, raw_ostream &OS) override {
     const auto *DR = dyn_cast<DeclRefExpr>(E);
@@ -3077,10 +3078,38 @@
       }
       return true;
     }
+    if (auto *Node = dyn_cast<CXXTemporaryObjectExpr>(E)) {
+      Node->getType().getCanonicalType().print(OS, Policy);
+      if (Node->isStdInitListInitialization())
+        /* Nothing to do; braces are part of creating the std::initializer_list.
+         */
+        ;
+      else if (Node->isListInitialization())
+        OS << "{";
+      else
+        OS << "(";
+      for (CXXTemporaryObjectExpr::arg_iterator Arg = Node->arg_begin(),
+                                                ArgEnd = Node->arg_end();
+           Arg != ArgEnd; ++Arg) {
+        if ((*Arg)->isDefaultArgument())
+          break;
+        if (Arg != Node->arg_begin())
+          OS << ", ";
+        (*Arg)->printPretty(OS, this, Policy);
+      }
+      if (Node->isStdInitListInitialization())
+        /* See above. */;
+      else if (Node->isListInitialization())
+        OS << "}";
+      else
+        OS << ")";
+      return true;
+    }
     return false;
   }
 
 private:
+  const ASTContext &Context;
   const PrintingPolicy Policy;
 };
 
@@ -3122,7 +3151,7 @@
   std::string Description;
   {
     llvm::raw_string_ostream Out(Description);
-    FailedBooleanConditionPrinterHelper Helper(getPrintingPolicy());
+    FailedBooleanConditionPrinterHelper Helper(Context, getPrintingPolicy());
     FailedCond->printPretty(Out, &Helper, getPrintingPolicy());
   }
   return { FailedCond, Description };

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