[PATCH] D55270: [Sema] Further improvements to to static_assert diagnostics.

[Clement Courbet via Phabricator via cfe-commits]

courbet created this revision.
courbet added reviewers: aaron.ballman, Quuxplusone.

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


Repository:
  rC Clang

https://reviews.llvm.org/D55270

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
@@ -111,6 +111,10 @@
 // expected-error at -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 at -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 at -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 at -1{{static_assert failed due to requirement '!(std::is_const<const int>::value)' "message"}}
 
 struct BI_tag {};
 struct RAI_tag : BI_tag {};
Index: lib/Sema/SemaTemplate.cpp
===================================================================
--- lib/Sema/SemaTemplate.cpp
+++ lib/Sema/SemaTemplate.cpp
@@ -3052,27 +3052,41 @@
   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:
+  FailedBooleanConditionPrinterHelper(const PrintingPolicy &Policy)
+      : Policy(Policy) {}
+
+  ~FailedBooleanConditionPrinterHelper() override {}
+
+  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;
+};
+
+} // namespace
 
 std::pair<Expr *, std::string>
 Sema::findFailedBooleanCondition(Expr *Cond, bool AllowTopLevelCond) {
@@ -3115,7 +3129,8 @@
   std::string Description;
   {
     llvm::raw_string_ostream Out(Description);
-    prettyPrintFailedBooleanCondition(Out, FailedCond, getPrintingPolicy());
+    FailedBooleanConditionPrinterHelper Helper(getPrintingPolicy());
+    FailedCond->printPretty(Out, &Helper, getPrintingPolicy());
   }
   return { FailedCond, Description };
 }


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