[clang] fix classification of a string literal expression used as initializer (#101447)

Author: mizvekov

clang/docs/ReleaseNotes.rst

@@ -130,7 +130,7 @@ Improvements to Clang's diagnostics
 - Some template related diagnostics have been improved.
 
   .. code-block:: c++
-    
+
      void foo() { template <typename> int i; } // error: templates can only be declared in namespace or class scope
 
      struct S {
@@ -170,6 +170,8 @@ Bug Fixes to C++ Support
 - Fixed a failed assertion when checking invalid delete operator declaration. (#GH96191)
 - Fix a crash when checking destructor reference with an invalid initializer. (#GH97230)
 - Clang now correctly parses potentially declarative nested-name-specifiers in pointer-to-member declarators.
+- Fix a crash when checking the initialzier of an object that was initialized
+  with a string literal. (#GH82167)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/AST/ExprClassification.cpp

@@ -119,12 +119,6 @@ static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
 
     // First come the expressions that are always lvalues, unconditionally.
   case Expr::ObjCIsaExprClass:
-    // C++ [expr.prim.general]p1: A string literal is an lvalue.
-  case Expr::StringLiteralClass:
-    // @encode is equivalent to its string
-  case Expr::ObjCEncodeExprClass:
-    // __func__ and friends are too.
-  case Expr::PredefinedExprClass:
     // Property references are lvalues
   case Expr::ObjCSubscriptRefExprClass:
   case Expr::ObjCPropertyRefExprClass:
@@ -150,6 +144,26 @@ static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
   case Expr::OMPIteratorExprClass:
     return Cl::CL_LValue;
 
+    // C++ [expr.prim.general]p1: A string literal is an lvalue.
+  case Expr::StringLiteralClass:
+    // @encode is equivalent to its string
+  case Expr::ObjCEncodeExprClass:
+    // Except we special case them as prvalues when they are used to
+    // initialize a char array.
+    return E->isLValue() ? Cl::CL_LValue : Cl::CL_PRValue;
+
+    // __func__ and friends are too.
+    // The char array initialization special case also applies
+    // when they are transparent.
+  case Expr::PredefinedExprClass: {
+    auto *PE = cast<PredefinedExpr>(E);
+    const StringLiteral *SL = PE->getFunctionName();
+    if (PE->isTransparent())
+      return SL ? ClassifyInternal(Ctx, SL) : Cl::CL_LValue;
+    assert(!SL || SL->isLValue());
+    return Cl::CL_LValue;
+  }
+
     // C99 6.5.2.5p5 says that compound literals are lvalues.
     // In C++, they're prvalue temporaries, except for file-scope arrays.
   case Expr::CompoundLiteralExprClass:

clang/test/SemaCXX/GH82167.cpp

@@ -0,0 +1,28 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c++23 -fsyntax-only -verify -xobjective-c++ %s
+// expected-no-diagnostics
+
+namespace t1 {
+  struct array {
+    char elems[2];
+  };
+
+  template <unsigned> struct Literal {
+    array arr;
+    constexpr Literal() : arr("") {}
+  };
+
+  template struct Literal<0>;
+} // namespace t1
+
+namespace t2 {
+  struct array {
+    char elems[2];
+  };
+
+  template <unsigned> struct Literal {
+    array arr;
+    constexpr Literal() : arr(@encode(int)) {}
+  };
+
+  template struct Literal<0>;
+} // namespace t2