[Sema] Further improvements to to static_assert diagnostics.

Summary:
We're now handling cases like `static_assert(!expr)` and
static_assert(!(expr))`.

Reviewers: aaron.ballman, Quuxplusone

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D55270

llvm-svn: 348741

clang/include/clang/Sema/Sema.h

@@ -2861,11 +2861,7 @@ class Sema {
 
   /// Find the failed Boolean condition within a given Boolean
   /// constant expression, and describe it with a string.
-  ///
-  /// \param AllowTopLevelCond Whether to allow the result to be the
-  /// complete top-level condition.
-  std::pair<Expr *, std::string>
-  findFailedBooleanCondition(Expr *Cond, bool AllowTopLevelCond);
+  std::pair<Expr *, std::string> findFailedBooleanCondition(Expr *Cond);
 
   /// Emit diagnostics for the diagnose_if attributes on Function, ignoring any
   /// non-ArgDependent DiagnoseIfAttrs.

clang/lib/Sema/SemaDeclCXX.cpp

@@ -13878,8 +13878,7 @@ Decl *Sema::BuildStaticAssertDeclaration(SourceLocation StaticAssertLoc,
       Expr *InnerCond = nullptr;
       std::string InnerCondDescription;
       std::tie(InnerCond, InnerCondDescription) =
-        findFailedBooleanCondition(Converted.get(),
-                                   /*AllowTopLevelCond=*/false);
+        findFailedBooleanCondition(Converted.get());
       if (InnerCond) {
         Diag(StaticAssertLoc, diag::err_static_assert_requirement_failed)
           << InnerCondDescription << !AssertMessage

clang/lib/Sema/SemaTemplate.cpp

@@ -3052,30 +3052,42 @@ static Expr *lookThroughRangesV3Condition(Preprocessor &PP, Expr *Cond) {
   return Cond;
 }
 
-// Print a diagnostic for the failing static_assert expression. Defaults to
-// pretty-printing the expression.
-static void prettyPrintFailedBooleanCondition(llvm::raw_string_ostream &OS,
-                                              const Expr *FailedCond,
-                                              const PrintingPolicy &Policy) {
-  const auto *DR = dyn_cast<DeclRefExpr>(FailedCond);
-  if (DR && DR->getQualifier()) {
-    // If this is a qualified name, expand the template arguments in nested
-    // qualifiers.
-    DR->getQualifier()->print(OS, Policy, true);
-    // Then print the decl itself.
-    const ValueDecl *VD = DR->getDecl();
-    OS << VD->getName();
-    if (const auto *IV = dyn_cast<VarTemplateSpecializationDecl>(VD)) {
-      // This is a template variable, print the expanded template arguments.
-      printTemplateArgumentList(OS, IV->getTemplateArgs().asArray(), Policy);
+namespace {
+
+// A PrinterHelper that prints more helpful diagnostics for some sub-expressions
+// within failing boolean expression, such as substituting template parameters
+// for actual types.
+class FailedBooleanConditionPrinterHelper : public PrinterHelper {
+public:
+  explicit FailedBooleanConditionPrinterHelper(const PrintingPolicy &Policy)
+      : Policy(Policy) {}
+
+  bool handledStmt(Stmt *E, raw_ostream &OS) override {
+    const auto *DR = dyn_cast<DeclRefExpr>(E);
+    if (DR && DR->getQualifier()) {
+      // If this is a qualified name, expand the template arguments in nested
+      // qualifiers.
+      DR->getQualifier()->print(OS, Policy, true);
+      // Then print the decl itself.
+      const ValueDecl *VD = DR->getDecl();
+      OS << VD->getName();
+      if (const auto *IV = dyn_cast<VarTemplateSpecializationDecl>(VD)) {
+        // This is a template variable, print the expanded template arguments.
+        printTemplateArgumentList(OS, IV->getTemplateArgs().asArray(), Policy);
+      }
+      return true;
     }
-    return;
+    return false;
   }
-  FailedCond->printPretty(OS, nullptr, Policy);
-}
+
+private:
+  const PrintingPolicy &Policy;
+};
+
+} // end anonymous namespace
 
 std::pair<Expr *, std::string>
-Sema::findFailedBooleanCondition(Expr *Cond, bool AllowTopLevelCond) {
+Sema::findFailedBooleanCondition(Expr *Cond) {
   Cond = lookThroughRangesV3Condition(PP, Cond);
 
   // Separate out all of the terms in a conjunction.
@@ -3087,11 +3099,6 @@ Sema::findFailedBooleanCondition(Expr *Cond, bool AllowTopLevelCond) {
   for (Expr *Term : Terms) {
     Expr *TermAsWritten = Term->IgnoreParenImpCasts();
 
-    // Literals are uninteresting.
-    if (isa<CXXBoolLiteralExpr>(TermAsWritten) ||
-        isa<IntegerLiteral>(TermAsWritten))
-      continue;
-
     // The initialization of the parameter from the argument is
     // a constant-evaluated context.
     EnterExpressionEvaluationContext ConstantEvaluated(
@@ -3104,18 +3111,18 @@ Sema::findFailedBooleanCondition(Expr *Cond, bool AllowTopLevelCond) {
       break;
     }
   }
-
-  if (!FailedCond) {
-    if (!AllowTopLevelCond)
-      return { nullptr, "" };
-
+  if (!FailedCond)
     FailedCond = Cond->IgnoreParenImpCasts();
-  }
+
+  // Literals are uninteresting.
+  if (isa<CXXBoolLiteralExpr>(FailedCond) || isa<IntegerLiteral>(FailedCond))
+    return {nullptr, ""};
 
   std::string Description;
   {
     llvm::raw_string_ostream Out(Description);
-    prettyPrintFailedBooleanCondition(Out, FailedCond, getPrintingPolicy());
+    FailedBooleanConditionPrinterHelper Helper(getPrintingPolicy());
+    FailedCond->printPretty(Out, &Helper, getPrintingPolicy());
   }
   return { FailedCond, Description };
 }
@@ -3199,9 +3206,7 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
             Expr *FailedCond;
             std::string FailedDescription;
             std::tie(FailedCond, FailedDescription) =
-              findFailedBooleanCondition(
-                TemplateArgs[0].getSourceExpression(),
-                /*AllowTopLevelCond=*/true);
+              findFailedBooleanCondition(TemplateArgs[0].getSourceExpression());
 
             // Remove the old SFINAE diagnostic.
             PartialDiagnosticAt OldDiag =
@@ -9649,7 +9654,7 @@ Sema::CheckTypenameType(ElaboratedTypeKeyword Keyword,
         Expr *FailedCond;
         std::string FailedDescription;
         std::tie(FailedCond, FailedDescription) =
-          findFailedBooleanCondition(Cond, /*AllowTopLevelCond=*/true);
+          findFailedBooleanCondition(Cond);
 
         Diag(FailedCond->getExprLoc(),
              diag::err_typename_nested_not_found_requirement)

clang/test/PCH/cxx-static_assert.cpp

@@ -3,7 +3,7 @@
 
 // Test with pch.
 // RUN: %clang_cc1 -std=c++11 -emit-pch -o %t %s
-// RUN: %clang_cc1 -include-pch %t -verify -std=c++11 %s 
+// RUN: %clang_cc1 -include-pch %t -verify -std=c++11 %s
 
 #ifndef HEADER
 #define HEADER
@@ -14,7 +14,7 @@ template<int N> struct T {
 
 #else
 
-// expected-error@12 {{static_assert failed "N is not 2!"}}
+// expected-error@12 {{static_assert failed due to requirement '1 == 2' "N is not 2!"}}
 T<1> t1; // expected-note {{in instantiation of template class 'T<1>' requested here}}
 T<2> t2;
 

clang/test/Sema/static-assert.c

@@ -38,5 +38,5 @@ struct A {
 
 typedef UNION(unsigned, struct A) U1;
 UNION(char[2], short) u2 = { .one = { 'a', 'b' } };
-typedef UNION(char, short) U3; // expected-error {{static_assert failed "type size mismatch"}}
+typedef UNION(char, short) U3; // expected-error {{static_assert failed due to requirement 'sizeof(char) == sizeof(short)' "type size mismatch"}}
 typedef UNION(float, 0.5f) U4; // expected-error {{expected a type}}

clang/test/SemaCXX/static-assert-cxx17.cpp

@@ -45,3 +45,12 @@ void foo4() {
 };
 template void foo4<float>();
 // expected-note@-1{{in instantiation of function template specialization 'foo4<float>' requested here}}
+
+
+template <typename U, typename V>
+void foo5() {
+  static_assert(!!(global_inline_var<U, V>));
+  // expected-error@-1{{static_assert failed due to requirement '!!(global_inline_var<int, float>)'}}
+}
+template void foo5<int, float>();
+// expected-note@-1{{in instantiation of function template specialization 'foo5<int, float>' requested here}}

clang/test/SemaCXX/static-assert.cpp

@@ -15,14 +15,14 @@ class C {
 };
 
 template<int N> struct T {
-    static_assert(N == 2, "N is not 2!"); // expected-error {{static_assert failed "N is not 2!"}}
+    static_assert(N == 2, "N is not 2!"); // expected-error {{static_assert failed due to requirement '1 == 2' "N is not 2!"}}
 };
 
 T<1> t1; // expected-note {{in instantiation of template class 'T<1>' requested here}}
 T<2> t2;
 
 template<typename T> struct S {
-    static_assert(sizeof(T) > sizeof(char), "Type not big enough!"); // expected-error {{static_assert failed "Type not big enough!"}}
+    static_assert(sizeof(T) > sizeof(char), "Type not big enough!"); // expected-error {{static_assert failed due to requirement 'sizeof(char) > sizeof(char)' "Type not big enough!"}}
 };
 
 S<char> s1; // expected-note {{in instantiation of template class 'S<char>' requested here}}
@@ -111,6 +111,14 @@ static_assert(std::is_same<ExampleTypes::T, ExampleTypes::U>::value, "message");
 // expected-error@-1{{static_assert failed due to requirement 'std::is_same<int, float>::value' "message"}}
 static_assert(std::is_const<ExampleTypes::T>::value, "message");
 // expected-error@-1{{static_assert failed due to requirement 'std::is_const<int>::value' "message"}}
+static_assert(!std::is_const<const ExampleTypes::T>::value, "message");
+// expected-error@-1{{static_assert failed due to requirement '!std::is_const<const int>::value' "message"}}
+static_assert(!(std::is_const<const ExampleTypes::T>::value), "message");
+// expected-error@-1{{static_assert failed due to requirement '!(std::is_const<const int>::value)' "message"}}
+static_assert(std::is_const<const ExampleTypes::T>::value == false, "message");
+// 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"}}
 
 struct BI_tag {};
 struct RAI_tag : BI_tag {};