[AST/CSGen] Move expanded pack collection into constraint generator

This is going to help us identify and fix positions were 'each'
keyword is mising.

Author: xedin

include/swift/AST/Expr.h

@@ -3627,8 +3627,6 @@ class PackExpansionExpr final : public Expr {
     PatternExpr = patternExpr;
   }
 
-  void getExpandedPacks(SmallVectorImpl<ASTNode> &packs);
-
   GenericEnvironment *getGenericEnvironment() {
     return Environment;
   }

lib/AST/Expr.cpp

@@ -1279,46 +1279,6 @@ PackExpansionExpr::create(ASTContext &ctx, SourceLoc repeatLoc,
                                      implicit, type);
 }
 
-void PackExpansionExpr::getExpandedPacks(SmallVectorImpl<ASTNode> &packs) {
-  struct PackCollector : public ASTWalker {
-    llvm::SmallVector<ASTNode, 2> packs;
-
-    /// Walk everything that's available.
-    MacroWalking getMacroWalkingBehavior() const override {
-      return MacroWalking::ArgumentsAndExpansion;
-    }
-
-    virtual PreWalkResult<Expr *> walkToExprPre(Expr *E) override {
-      // Don't walk into nested pack expansions
-      if (isa<PackExpansionExpr>(E)) {
-        return Action::SkipChildren(E);
-      }
-
-      if (isa<PackElementExpr>(E)) {
-        packs.push_back(E);
-      }
-
-      return Action::Continue(E);
-    }
-
-    virtual PreWalkAction walkToTypeReprPre(TypeRepr *T) override {
-      // Don't walk into nested pack expansions
-      if (isa<PackExpansionTypeRepr>(T)) {
-        return Action::SkipChildren();
-      }
-
-      if (isa<PackElementTypeRepr>(T)) {
-        packs.push_back(T);
-      }
-
-      return Action::Continue();
-    }
-  } packCollector;
-
-  getPatternExpr()->walk(packCollector);
-  packs.append(packCollector.packs.begin(), packCollector.packs.end());
-}
-
 PackElementExpr *
 PackElementExpr::create(ASTContext &ctx, SourceLoc eachLoc, Expr *packRefExpr,
                         bool implicit, Type type) {

lib/Sema/CSGen.cpp

@@ -3063,6 +3063,50 @@ namespace {
       return variadicSeq;
     }
 
+    void collectExpandedPacks(PackExpansionExpr *expansion,
+                              SmallVectorImpl<ASTNode> &packs) {
+      struct PackCollector : public ASTWalker {
+      private:
+        SmallVectorImpl<ASTNode> &Packs;
+
+      public:
+        PackCollector(SmallVectorImpl<ASTNode> &packs) : Packs(packs) {}
+
+        /// Walk everything that's available.
+        MacroWalking getMacroWalkingBehavior() const override {
+          return MacroWalking::ArgumentsAndExpansion;
+        }
+
+        virtual PreWalkResult<Expr *> walkToExprPre(Expr *E) override {
+          // Don't walk into nested pack expansions
+          if (isa<PackExpansionExpr>(E)) {
+            return Action::SkipChildren(E);
+          }
+
+          if (isa<PackElementExpr>(E)) {
+            Packs.push_back(E);
+          }
+
+          return Action::Continue(E);
+        }
+
+        virtual PreWalkAction walkToTypeReprPre(TypeRepr *T) override {
+          // Don't walk into nested pack expansions
+          if (isa<PackExpansionTypeRepr>(T)) {
+            return Action::SkipChildren();
+          }
+
+          if (isa<PackElementTypeRepr>(T)) {
+            Packs.push_back(T);
+          }
+
+          return Action::Continue();
+        }
+      } packCollector(packs);
+
+      expansion->getPatternExpr()->walk(packCollector);
+    }
+
     Type visitPackExpansionExpr(PackExpansionExpr *expr) {
       assert(PackElementEnvironments.back() == expr);
       PackElementEnvironments.pop_back();
@@ -3086,7 +3130,7 @@ namespace {
       // Generate ShapeOf constraints between all packs expanded by this
       // pack expansion expression through the shape type variable.
       SmallVector<ASTNode, 2> expandedPacks;
-      expr->getExpandedPacks(expandedPacks);
+      collectExpandedPacks(expr, expandedPacks);
 
       if (expandedPacks.empty()) {
         (void)CS.recordFix(AllowValueExpansionWithoutPackReferences::create(