[AST] Add the skeleton for PackExpansionExpr.

include/swift/AST/Expr.h

@@ -3527,6 +3527,51 @@ class VarargExpansionExpr : public Expr {
   }
 };
 
+/// A pack expansion expression is a pattern expression followed by
+/// the expansion operator '...'. The pattern expression contains
+/// references to parameter packs of length N, and the expansion
+/// operator will repeat the pattern N times.
+///
+/// Pack expansion expressions are permitted in expression contexts
+/// that naturally accept a comma-separated list of values, including
+/// call argument lists, the elements of a tuple value, and the source
+/// of a for-in loop.
+class PackExpansionExpr: public Expr {
+  Expr *PatternExpr;
+  SourceLoc DotsLoc;
+
+  PackExpansionExpr(Expr *patternExpr,
+                    SourceLoc dotsLoc,
+                    bool implicit, Type type)
+    : Expr(ExprKind::PackExpansion, implicit, type),
+      PatternExpr(patternExpr), DotsLoc(dotsLoc) {}
+
+public:
+  static PackExpansionExpr *create(ASTContext &ctx,
+                                   Expr *patternExpr,
+                                   SourceLoc dotsLoc,
+                                   bool implicit = false,
+                                   Type type = Type());
+
+  Expr *getPatternExpr() const { return PatternExpr; }
+
+  void setPatternExpr(Expr *patternExpr) {
+    PatternExpr = patternExpr;
+  }
+
+  SourceLoc getStartLoc() const {
+    return PatternExpr->getStartLoc();
+  }
+
+  SourceLoc getEndLoc() const {
+    return DotsLoc;
+  }
+
+  static bool classof(const Expr *E) {
+    return E->getKind() == ExprKind::PackExpansion;
+  }
+};
+
 /// SequenceExpr - A list of binary operations which has not yet been
 /// folded into a tree.  The operands all have even indices, while the
 /// subexpressions with odd indices are all (potentially overloaded)

include/swift/AST/ExprNodes.def

@@ -129,6 +129,7 @@ ABSTRACT_EXPR(AbstractClosure, Expr)
   EXPR_RANGE(AbstractClosure, Closure, AutoClosure)
 EXPR(InOut, Expr)
 EXPR(VarargExpansion, Expr)
+EXPR(PackExpansion, Expr)
 EXPR(DynamicType, Expr)
 EXPR(RebindSelfInConstructor, Expr)
 EXPR(OpaqueValue, Expr)

lib/AST/ASTDumper.cpp

@@ -2432,6 +2432,12 @@ class PrintExpr : public ExprVisitor<PrintExpr> {
     PrintWithColorRAII(OS, ParenthesisColor) << ')';
   }
 
+  void visitPackExpansionExpr(PackExpansionExpr *E) {
+    printCommon(E, "pack_expansion_expr") << "\n";
+    printRec(E->getPatternExpr());
+    PrintWithColorRAII(OS, ParenthesisColor) << ')';
+  }
+
   void visitForceTryExpr(ForceTryExpr *E) {
     printCommon(E, "force_try_expr");
     OS << '\n';

lib/AST/ASTPrinter.cpp

@@ -4750,6 +4750,10 @@ void PrintAST::visitVarargExpansionExpr(VarargExpansionExpr *expr) {
   visit(expr->getSubExpr());
 }
 
+void PrintAST::visitPackExpansionExpr(PackExpansionExpr *expr) {
+  visit(expr->getPatternExpr());
+}
+
 void PrintAST::visitArchetypeToSuperExpr(ArchetypeToSuperExpr *expr) {
 }
 

lib/AST/ASTWalker.cpp

@@ -829,6 +829,14 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
     return nullptr;
   }
 
+  Expr *visitPackExpansionExpr(PackExpansionExpr *E) {
+    if (Expr *pattern = doIt(E->getPatternExpr())) {
+      E->setPatternExpr(pattern);
+      return E;
+    }
+    return nullptr;
+  }
+
   Expr *visitSequenceExpr(SequenceExpr *E) {
     for (unsigned i = 0, e = E->getNumElements(); i != e; ++i)
       if (Expr *Elt = doIt(E->getElement(i)))

lib/AST/Expr.cpp

@@ -389,6 +389,7 @@ ConcreteDeclRef Expr::getReferencedDecl(bool stopAtParenExpr) const {
   PASS_THROUGH_REFERENCE(InOut, getSubExpr);
 
   NO_REFERENCE(VarargExpansion);
+  NO_REFERENCE(PackExpansion);
   NO_REFERENCE(DynamicType);
 
   PASS_THROUGH_REFERENCE(RebindSelfInConstructor, getSubExpr);
@@ -745,6 +746,7 @@ bool Expr::canAppendPostfixExpression(bool appendingPostfixOperator) const {
   case ExprKind::OpenExistential:
   case ExprKind::MakeTemporarilyEscapable:
   case ExprKind::VarargExpansion:
+  case ExprKind::PackExpansion:
     return false;
 
   case ExprKind::Call:
@@ -918,6 +920,7 @@ bool Expr::isValidParentOfTypeExpr(Expr *typeExpr) const {
   case ExprKind::AutoClosure:
   case ExprKind::InOut:
   case ExprKind::VarargExpansion:
+  case ExprKind::PackExpansion:
   case ExprKind::DynamicType:
   case ExprKind::RebindSelfInConstructor:
   case ExprKind::OpaqueValue:
@@ -1235,6 +1238,14 @@ VarargExpansionExpr *VarargExpansionExpr::createArrayExpansion(ASTContext &ctx,
   return new (ctx) VarargExpansionExpr(AE, /*implicit*/ true, AE->getType());
 }
 
+PackExpansionExpr *
+PackExpansionExpr::create(ASTContext &ctx, Expr *patternExpr,
+                          SourceLoc dotsLoc, bool implicit,
+                          Type type) {
+  return new (ctx) PackExpansionExpr(patternExpr, dotsLoc,
+                                     implicit, type);
+}
+
 SequenceExpr *SequenceExpr::create(ASTContext &ctx, ArrayRef<Expr*> elements) {
   assert(elements.size() & 1 && "even number of elements in sequence");
   size_t bytes = totalSizeToAlloc<Expr *>(elements.size());

lib/SILGen/SILGenExpr.cpp

@@ -447,6 +447,7 @@ namespace {
              SGFContext C);
     RValue visitBridgeToObjCExpr(BridgeToObjCExpr *E, SGFContext C);
     RValue visitReifyPackExpr(ReifyPackExpr *E, SGFContext C);
+    RValue visitPackExpansionExpr(PackExpansionExpr *E, SGFContext C);
     RValue visitBridgeFromObjCExpr(BridgeFromObjCExpr *E, SGFContext C);
     RValue visitConditionalBridgeFromObjCExpr(ConditionalBridgeFromObjCExpr *E,
                                               SGFContext C);
@@ -1517,6 +1518,12 @@ RValueEmitter::visitReifyPackExpr(ReifyPackExpr *E, SGFContext C) {
   llvm_unreachable("Unimplemented!");
 }
 
+RValue
+RValueEmitter::visitPackExpansionExpr(PackExpansionExpr *E,
+                                      SGFContext C) {
+  llvm_unreachable("not implemented for PackExpansionExpr");
+}
+
 RValue RValueEmitter::visitArchetypeToSuperExpr(ArchetypeToSuperExpr *E,
                                                 SGFContext C) {
   ManagedValue archetype = SGF.emitRValueAsSingleValue(E->getSubExpr());

lib/Sema/CSApply.cpp

@@ -3692,6 +3692,10 @@ namespace {
       return expr;
     }
 
+    Expr *visitPackExpansionExpr(PackExpansionExpr *expr) {
+      llvm_unreachable("not implemented for PackExpansionExpr");
+    }
+
     Expr *visitDynamicTypeExpr(DynamicTypeExpr *expr) {
       Expr *base = expr->getBase();
       base = cs.coerceToRValue(base);

lib/Sema/CSGen.cpp

@@ -2885,6 +2885,10 @@ namespace {
       return variadicSeq;
     }
 
+    Type visitPackExpansionExpr(PackExpansionExpr *expr) {
+      llvm_unreachable("not implemented for PackExpansionExpr");
+    }
+
     Type visitDynamicTypeExpr(DynamicTypeExpr *expr) {
       auto tv = CS.createTypeVariable(CS.getConstraintLocator(expr),
                                       TVO_CanBindToNoEscape);