[Clang] [C++26] Expansion Statements (Part 7: Constexpr support and tests)

clang/lib/AST/ExprConstant.cpp

@@ -6037,6 +6037,12 @@ static EvalStmtResult EvaluateStmt(StmtResult &Result, EvalInfo &Info,
       const VarDecl *VD = dyn_cast_or_null<VarDecl>(D);
       if (VD && !CheckLocalVariableDeclaration(Info, VD))
         return ESR_Failed;
+
+      if (const auto *ESD = dyn_cast<CXXExpansionStmtDecl>(D)) {
+        assert(ESD->getInstantiations() && "not expanded?");
+        return EvaluateStmt(Result, Info, ESD->getInstantiations(), Case);
+      }
+
       // Each declaration initialization is its own full-expression.
       FullExpressionRAII Scope(Info);
       if (!EvaluateDecl(Info, D, /*EvaluateConditionDecl=*/true) &&
@@ -6309,6 +6315,40 @@ static EvalStmtResult EvaluateStmt(StmtResult &Result, EvalInfo &Info,
     return Scope.destroy() ? ESR_Succeeded : ESR_Failed;
   }
 
+  case Stmt::CXXExpansionStmtInstantiationClass: {
+    BlockScopeRAII Scope(Info);
+    const auto *Expansion = cast<CXXExpansionStmtInstantiation>(S);
+    for (const Stmt *Shared : Expansion->getSharedStmts()) {
+      EvalStmtResult ESR = EvaluateStmt(Result, Info, Shared);
+      if (ESR != ESR_Succeeded) {
+        if (ESR != ESR_Failed && !Scope.destroy())
+          return ESR_Failed;
+        return ESR;
+      }
+    }
+
+    // No need to push an extra scope for these since they're already
+    // CompoundStmts.
+    EvalStmtResult ESR = ESR_Succeeded;
+    for (const Stmt *Instantiation : Expansion->getInstantiations()) {
+      ESR = EvaluateStmt(Result, Info, Instantiation);
+      if (ESR == ESR_Failed ||
+          ShouldPropagateBreakContinue(Info, Expansion, &Scope, ESR))
+        return ESR;
+      if (ESR != ESR_Continue) {
+        // Succeeded here actually means we encountered a 'break'.
+        assert(ESR == ESR_Succeeded || ESR == ESR_Returned);
+        break;
+      }
+    }
+
+    // Map Continue back to Succeeded if we fell off the end of the loop.
+    if (ESR == ESR_Continue)
+      ESR = ESR_Succeeded;
+
+    return Scope.destroy() ? ESR : ESR_Failed;
+  }
+
   case Stmt::SwitchStmtClass:
     return EvaluateSwitch(Result, Info, cast<SwitchStmt>(S));
 

clang/lib/Sema/SemaDeclCXX.cpp

@@ -2027,6 +2027,9 @@ static bool CheckConstexprDeclStmt(Sema &SemaRef, const FunctionDecl *Dcl,
       //   - using-enum-declaration
       continue;
 
+    case Decl::CXXExpansionStmt:
+      continue;
+
     case Decl::Typedef:
     case Decl::TypeAlias: {
       //   - typedef declarations and alias-declarations that do not define