Reland [clang] Make predefined expressions string literals under -fms…

…-extensions

MSVC makes these string literals [1][2].

[1] https://godbolt.org/z/6vnTzbExx
[2] https://learn.microsoft.com/en-us/cpp/preprocessor/predefined-macros?view=msvc-170

Fixes #114

Initial commit didn't check if there was a function name when stepping through expressions ignoring parens.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D146764

clang/docs/ReleaseNotes.rst

@@ -438,6 +438,9 @@ Bug Fixes to C++ Support
 - Fix a crash when expanding a pack as the index of a subscript expression.
 - Fix handling of constexpr dynamic memory allocations in template
   arguments. (`#62462 <https://github.com/llvm/llvm-project/issues/62462>`_)
+- Some predefined expressions are now treated as string literals in MSVC
+  compatibility mode.
+  (`#114 <https://github.com/llvm/llvm-project/issues/114>`_)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/AST/Expr.h

@@ -1992,7 +1992,7 @@ class PredefinedExpr final
 
 private:
   PredefinedExpr(SourceLocation L, QualType FNTy, IdentKind IK,
-                 StringLiteral *SL);
+                 bool IsTransparent, StringLiteral *SL);
 
   explicit PredefinedExpr(EmptyShell Empty, bool HasFunctionName);
 
@@ -2007,8 +2007,12 @@ class PredefinedExpr final
 
 public:
   /// Create a PredefinedExpr.
+  ///
+  /// If IsTransparent, the PredefinedExpr is transparently handled as a
+  /// StringLiteral.
   static PredefinedExpr *Create(const ASTContext &Ctx, SourceLocation L,
-                                QualType FNTy, IdentKind IK, StringLiteral *SL);
+                                QualType FNTy, IdentKind IK, bool IsTransparent,
+                                StringLiteral *SL);
 
   /// Create an empty PredefinedExpr.
   static PredefinedExpr *CreateEmpty(const ASTContext &Ctx,
@@ -2018,6 +2022,8 @@ class PredefinedExpr final
     return static_cast<IdentKind>(PredefinedExprBits.Kind);
   }
 
+  bool isTransparent() const { return PredefinedExprBits.IsTransparent; }
+
   SourceLocation getLocation() const { return PredefinedExprBits.Loc; }
   void setLocation(SourceLocation L) { PredefinedExprBits.Loc = L; }
 

clang/include/clang/AST/IgnoreExpr.h

@@ -166,6 +166,11 @@ inline Expr *IgnoreParensSingleStep(Expr *E) {
       return CE->getChosenSubExpr();
   }
 
+  else if (auto *PE = dyn_cast<PredefinedExpr>(E)) {
+    if (PE->isTransparent() && PE->getFunctionName())
+      return PE->getFunctionName();
+  }
+
   return E;
 }
 

clang/include/clang/AST/Stmt.h

@@ -364,6 +364,10 @@ class alignas(void *) Stmt {
     /// for the predefined identifier.
     unsigned HasFunctionName : 1;
 
+    /// True if this PredefinedExpr should be treated as a StringLiteral (for
+    /// MSVC compatibility).
+    unsigned IsTransparent : 1;
+
     /// The location of this PredefinedExpr.
     SourceLocation Loc;
   };

clang/include/clang/Basic/DiagnosticGroups.td

@@ -1190,6 +1190,7 @@ def MicrosoftCommentPaste : DiagGroup<"microsoft-comment-paste">;
 def MicrosoftEndOfFile : DiagGroup<"microsoft-end-of-file">;
 def MicrosoftInaccessibleBase : DiagGroup<"microsoft-inaccessible-base">;
 def MicrosoftStaticAssert : DiagGroup<"microsoft-static-assert">;
+def MicrosoftInitFromPredefined : DiagGroup<"microsoft-init-from-predefined">;
 
 // Aliases.
 def : DiagGroup<"msvc-include", [MicrosoftInclude]>;
@@ -1207,7 +1208,7 @@ def Microsoft : DiagGroup<"microsoft",
      MicrosoftFlexibleArray, MicrosoftExtraQualification, MicrosoftCast,
      MicrosoftConstInit, MicrosoftVoidPseudoDtor, MicrosoftAnonTag,
      MicrosoftCommentPaste, MicrosoftEndOfFile, MicrosoftStaticAssert,
-     MicrosoftInconsistentDllImport]>;
+     MicrosoftInitFromPredefined, MicrosoftInconsistentDllImport]>;
 
 def ClangClPch : DiagGroup<"clang-cl-pch">;
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -112,6 +112,9 @@ def err_expr_not_string_literal : Error<"expression is not a string literal">;
 def ext_predef_outside_function : Warning<
   "predefined identifier is only valid inside function">,
   InGroup<DiagGroup<"predefined-identifier-outside-function">>;
+def ext_init_from_predefined : ExtWarn<
+  "initializing an array from a '%0' predefined identifier is a Microsoft extension">,
+  InGroup<MicrosoftInitFromPredefined>;
 def warn_float_overflow : Warning<
   "magnitude of floating-point constant too large for type %0; maximum is %1">,
    InGroup<LiteralRange>;

clang/lib/AST/ASTImporter.cpp

@@ -7068,7 +7068,8 @@ ExpectedStmt ASTNodeImporter::VisitPredefinedExpr(PredefinedExpr *E) {
     return std::move(Err);
 
   return PredefinedExpr::Create(Importer.getToContext(), ToBeginLoc, ToType,
-                                E->getIdentKind(), ToFunctionName);
+                                E->getIdentKind(), E->isTransparent(),
+                                ToFunctionName);
 }
 
 ExpectedStmt ASTNodeImporter::VisitDeclRefExpr(DeclRefExpr *E) {

clang/lib/AST/Expr.cpp

@@ -663,13 +663,14 @@ std::string SYCLUniqueStableNameExpr::ComputeName(ASTContext &Context,
 }
 
 PredefinedExpr::PredefinedExpr(SourceLocation L, QualType FNTy, IdentKind IK,
-                               StringLiteral *SL)
+                               bool IsTransparent, StringLiteral *SL)
     : Expr(PredefinedExprClass, FNTy, VK_LValue, OK_Ordinary) {
   PredefinedExprBits.Kind = IK;
   assert((getIdentKind() == IK) &&
          "IdentKind do not fit in PredefinedExprBitfields!");
   bool HasFunctionName = SL != nullptr;
   PredefinedExprBits.HasFunctionName = HasFunctionName;
+  PredefinedExprBits.IsTransparent = IsTransparent;
   PredefinedExprBits.Loc = L;
   if (HasFunctionName)
     setFunctionName(SL);
@@ -683,11 +684,11 @@ PredefinedExpr::PredefinedExpr(EmptyShell Empty, bool HasFunctionName)
 
 PredefinedExpr *PredefinedExpr::Create(const ASTContext &Ctx, SourceLocation L,
                                        QualType FNTy, IdentKind IK,
-                                       StringLiteral *SL) {
+                                       bool IsTransparent, StringLiteral *SL) {
   bool HasFunctionName = SL != nullptr;
   void *Mem = Ctx.Allocate(totalSizeToAlloc<Stmt *>(HasFunctionName),
                            alignof(PredefinedExpr));
-  return new (Mem) PredefinedExpr(L, FNTy, IK, SL);
+  return new (Mem) PredefinedExpr(L, FNTy, IK, IsTransparent, SL);
 }
 
 PredefinedExpr *PredefinedExpr::CreateEmpty(const ASTContext &Ctx,

clang/lib/Sema/SemaExpr.cpp

@@ -3579,7 +3579,8 @@ ExprResult Sema::BuildPredefinedExpr(SourceLocation Loc,
     }
   }
 
-  return PredefinedExpr::Create(Context, Loc, ResTy, IK, SL);
+  return PredefinedExpr::Create(Context, Loc, ResTy, IK, LangOpts.MicrosoftExt,
+                                SL);
 }
 
 ExprResult Sema::BuildSYCLUniqueStableNameExpr(SourceLocation OpLoc,

clang/lib/Sema/SemaInit.cpp

@@ -174,6 +174,8 @@ static void updateStringLiteralType(Expr *E, QualType Ty) {
       E = GSE->getResultExpr();
     } else if (ChooseExpr *CE = dyn_cast<ChooseExpr>(E)) {
       E = CE->getChosenSubExpr();
+    } else if (PredefinedExpr *PE = dyn_cast<PredefinedExpr>(E)) {
+      E = PE->getFunctionName();
     } else {
       llvm_unreachable("unexpected expr in string literal init");
     }
@@ -8508,6 +8510,15 @@ ExprResult InitializationSequence::Perform(Sema &S,
         << Init->getSourceRange();
   }
 
+  if (S.getLangOpts().MicrosoftExt && Args.size() == 1 &&
+      isa<PredefinedExpr>(Args[0]) && Entity.getType()->isArrayType()) {
+    // Produce a Microsoft compatibility warning when initializing from a
+    // predefined expression since MSVC treats predefined expressions as string
+    // literals.
+    Expr *Init = Args[0];
+    S.Diag(Init->getBeginLoc(), diag::ext_init_from_predefined) << Init;
+  }
+
   // OpenCL v2.0 s6.13.11.1. atomic variables can be initialized in global scope
   QualType ETy = Entity.getType();
   bool HasGlobalAS = ETy.hasAddressSpace() &&

clang/lib/Serialization/ASTReaderStmt.cpp

@@ -582,6 +582,7 @@ void ASTStmtReader::VisitPredefinedExpr(PredefinedExpr *E) {
   bool HasFunctionName = Record.readInt();
   E->PredefinedExprBits.HasFunctionName = HasFunctionName;
   E->PredefinedExprBits.Kind = Record.readInt();
+  E->PredefinedExprBits.IsTransparent = Record.readInt();
   E->setLocation(readSourceLocation());
   if (HasFunctionName)
     E->setFunctionName(cast<StringLiteral>(Record.readSubExpr()));

clang/lib/Serialization/ASTWriterStmt.cpp

@@ -593,6 +593,7 @@ void ASTStmtWriter::VisitPredefinedExpr(PredefinedExpr *E) {
   bool HasFunctionName = E->getFunctionName() != nullptr;
   Record.push_back(HasFunctionName);
   Record.push_back(E->getIdentKind()); // FIXME: stable encoding
+  Record.push_back(E->isTransparent());
   Record.AddSourceLocation(E->getLocation());
   if (HasFunctionName)
     Record.AddStmt(E->getFunctionName());

clang/test/Modules/predefined.cpp

@@ -0,0 +1,27 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: cd %t
+
+// RUN: %clang_cc1 -x c++ -std=c++20 -emit-module-interface a.h -o a.pcm -fms-extensions -verify
+// RUN: %clang_cc1 -std=c++20 a.cpp -fmodule-file=A=a.pcm -fms-extensions -fsyntax-only -verify
+
+//--- a.h
+
+// expected-no-diagnostics
+
+export module A;
+
+export template <typename T>
+void f() {
+    char a[] = __func__;
+}
+
+//--- a.cpp
+
+// expected-warning@a.h:8 {{initializing an array from a '__func__' predefined identifier is a Microsoft extension}}
+
+import A;
+
+void g() {
+    f<int>(); // expected-note {{in instantiation of function template specialization 'f<int>' requested here}}
+}

clang/test/Sema/ms_predefined_expr.cpp

@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 %s -fsyntax-only -Wmicrosoft -verify -fms-extensions
+
+void f() {
+ const char a[] = __FUNCTION__; // expected-warning{{initializing an array from a '__FUNCTION__' predefined identifier is a Microsoft extension}}
+ const char b[] = __FUNCDNAME__; // expected-warning{{initializing an array from a '__FUNCDNAME__' predefined identifier is a Microsoft extension}}
+ const char c[] = __FUNCSIG__; // expected-warning{{initializing an array from a '__FUNCSIG__' predefined identifier is a Microsoft extension}}
+ const char d[] = __func__; // expected-warning{{initializing an array from a '__func__' predefined identifier is a Microsoft extension}}
+ const char e[] = __PRETTY_FUNCTION__; // expected-warning{{initializing an array from a '__PRETTY_FUNCTION__' predefined identifier is a Microsoft extension}}
+}

clang/test/SemaCXX/predefined-expr-msvc.cpp

@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 %s -std=c++17 -fsyntax-only -verify
+// RUN: %clang_cc1 %s -std=c++17 -fsyntax-only -verify -fms-extensions
+
+// expected-no-diagnostics
+
+struct StringRef {
+  StringRef(const char *);
+};
+template <typename T>
+StringRef getTypeName() {
+  StringRef s = __func__;
+}
+