PR45083: Mark statement expressions as being dependent if they appear in

dependent contexts.

We previously assumed they were neither value- nor
instantiation-dependent under any circumstances, which would lead to
crashes and other misbehavior.

(cherry picked from commit bdad0a1)

Author: zygoloid

clang/include/clang/AST/Expr.h

@@ -3955,14 +3955,14 @@ class StmtExpr : public Expr {
   Stmt *SubStmt;
   SourceLocation LParenLoc, RParenLoc;
 public:
-  // FIXME: Does type-dependence need to be computed differently?
-  // FIXME: Do we need to compute instantiation instantiation-dependence for
-  // statements? (ugh!)
   StmtExpr(CompoundStmt *substmt, QualType T,
-           SourceLocation lp, SourceLocation rp) :
+           SourceLocation lp, SourceLocation rp, bool InDependentContext) :
+    // Note: we treat a statement-expression in a dependent context as always
+    // being value- and instantiation-dependent. This matches the behavior of
+    // lambda-expressions and GCC.
     Expr(StmtExprClass, T, VK_RValue, OK_Ordinary,
-         T->isDependentType(), false, false, false),
-    SubStmt(substmt), LParenLoc(lp), RParenLoc(rp) { }
+         T->isDependentType(), InDependentContext, InDependentContext, false),
+    SubStmt(substmt), LParenLoc(lp), RParenLoc(rp) {}
 
   /// Build an empty statement expression.
   explicit StmtExpr(EmptyShell Empty) : Expr(StmtExprClass, Empty) { }

clang/include/clang/Sema/Sema.h

@@ -4923,7 +4923,7 @@ class Sema final {
                             LabelDecl *TheDecl);
 
   void ActOnStartStmtExpr();
-  ExprResult ActOnStmtExpr(SourceLocation LPLoc, Stmt *SubStmt,
+  ExprResult ActOnStmtExpr(Scope *S, SourceLocation LPLoc, Stmt *SubStmt,
                            SourceLocation RPLoc); // "({..})"
   // Handle the final expression in a statement expression.
   ExprResult ActOnStmtExprResult(ExprResult E);

clang/lib/AST/ASTImporter.cpp

@@ -6724,8 +6724,9 @@ ExpectedStmt ASTNodeImporter::VisitStmtExpr(StmtExpr *E) {
   SourceLocation ToLParenLoc, ToRParenLoc;
   std::tie(ToSubStmt, ToType, ToLParenLoc, ToRParenLoc) = *Imp;
 
-  return new (Importer.getToContext()) StmtExpr(
-      ToSubStmt, ToType, ToLParenLoc, ToRParenLoc);
+  return new (Importer.getToContext())
+      StmtExpr(ToSubStmt, ToType, ToLParenLoc, ToRParenLoc,
+               E->isInstantiationDependent());
 }
 
 ExpectedStmt ASTNodeImporter::VisitUnaryOperator(UnaryOperator *E) {

clang/lib/Parse/ParseExpr.cpp

@@ -2655,7 +2655,8 @@ Parser::ParseParenExpression(ParenParseOption &ExprType, bool stopIfCastExpr,
 
       // If the substmt parsed correctly, build the AST node.
       if (!Stmt.isInvalid()) {
-        Result = Actions.ActOnStmtExpr(OpenLoc, Stmt.get(), Tok.getLocation());
+        Result = Actions.ActOnStmtExpr(getCurScope(), OpenLoc, Stmt.get(),
+                                       Tok.getLocation());
       } else {
         Actions.ActOnStmtExprError();
       }

clang/lib/Sema/SemaExpr.cpp

@@ -13908,9 +13908,8 @@ void Sema::ActOnStmtExprError() {
   PopExpressionEvaluationContext();
 }
 
-ExprResult
-Sema::ActOnStmtExpr(SourceLocation LPLoc, Stmt *SubStmt,
-                    SourceLocation RPLoc) { // "({..})"
+ExprResult Sema::ActOnStmtExpr(Scope *S, SourceLocation LPLoc, Stmt *SubStmt,
+                               SourceLocation RPLoc) { // "({..})"
   assert(SubStmt && isa<CompoundStmt>(SubStmt) && "Invalid action invocation!");
   CompoundStmt *Compound = cast<CompoundStmt>(SubStmt);
 
@@ -13939,9 +13938,18 @@ Sema::ActOnStmtExpr(SourceLocation LPLoc, Stmt *SubStmt,
     }
   }
 
+  bool IsDependentContext = false;
+  if (S)
+    IsDependentContext = S->getTemplateParamParent() != nullptr;
+  else
+    // FIXME: This is not correct when substituting inside a templated
+    // context that isn't a DeclContext (such as a variable template).
+    IsDependentContext = CurContext->isDependentContext();
+
   // FIXME: Check that expression type is complete/non-abstract; statement
   // expressions are not lvalues.
-  Expr *ResStmtExpr = new (Context) StmtExpr(Compound, Ty, LPLoc, RPLoc);
+  Expr *ResStmtExpr =
+      new (Context) StmtExpr(Compound, Ty, LPLoc, RPLoc, IsDependentContext);
   if (StmtExprMayBindToTemp)
     return MaybeBindToTemporary(ResStmtExpr);
   return ResStmtExpr;

clang/lib/Sema/SemaExprCXX.cpp

@@ -6800,8 +6800,9 @@ Stmt *Sema::MaybeCreateStmtWithCleanups(Stmt *SubStmt) {
   // a new AsmStmtWithTemporaries.
   CompoundStmt *CompStmt = CompoundStmt::Create(
       Context, SubStmt, SourceLocation(), SourceLocation());
-  Expr *E = new (Context) StmtExpr(CompStmt, Context.VoidTy, SourceLocation(),
-                                   SourceLocation());
+  Expr *E = new (Context)
+      StmtExpr(CompStmt, Context.VoidTy, SourceLocation(), SourceLocation(),
+               CurContext->isDependentContext());
   return MaybeCreateExprWithCleanups(E);
 }
 

clang/lib/Sema/TreeTransform.h

@@ -2526,10 +2526,9 @@ class TreeTransform {
   ///
   /// By default, performs semantic analysis to build the new expression.
   /// Subclasses may override this routine to provide different behavior.
-  ExprResult RebuildStmtExpr(SourceLocation LParenLoc,
-                                   Stmt *SubStmt,
-                                   SourceLocation RParenLoc) {
-    return getSema().ActOnStmtExpr(LParenLoc, SubStmt, RParenLoc);
+  ExprResult RebuildStmtExpr(SourceLocation LParenLoc, Stmt *SubStmt,
+                             SourceLocation RParenLoc) {
+    return getSema().ActOnStmtExpr(nullptr, LParenLoc, SubStmt, RParenLoc);
   }
 
   /// Build a new __builtin_choose_expr expression.
@@ -11801,6 +11800,8 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
     NewTrailingRequiresClause = getDerived().TransformExpr(TRC);
 
   // Create the local class that will describe the lambda.
+  // FIXME: KnownDependent below is wrong when substituting inside a templated
+  // context that isn't a DeclContext (such as a variable template).
   CXXRecordDecl *OldClass = E->getLambdaClass();
   CXXRecordDecl *Class
     = getSema().createLambdaClosureType(E->getIntroducerRange(),

clang/test/SemaTemplate/dependent-expr.cpp

@@ -1,5 +1,4 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s
-// expected-no-diagnostics
 
 // PR5908
 template <typename Iterator>
@@ -108,3 +107,22 @@ namespace PR18152 {
   };
   template struct A<0>;
 }
+
+template<typename T> void stmt_expr_1() {
+  static_assert( ({ false; }), "" );
+}
+void stmt_expr_2() {
+  static_assert( ({ false; }), "" ); // expected-error {{failed}}
+}
+
+namespace PR45083 {
+  struct A { bool x; };
+
+  template<typename> struct B : A {
+    void f() {
+      const int n = ({ if (x) {} 0; });
+    }
+  };
+
+  template void B<int>::f();
+}