[MiscDiagnostics] Introduce a base class for diagnostic walkers

Put some common logic related to local declaration to the base
class and refactor other walkers to use it instead of `ASTWalker`.

Author: xedin

lib/Sema/MiscDiagnostics.cpp

@@ -24,6 +24,7 @@
 #include "swift/AST/NameLookupRequests.h"
 #include "swift/AST/Pattern.h"
 #include "swift/AST/SourceFile.h"
+#include "swift/AST/Stmt.h"
 #include "swift/AST/TypeCheckRequests.h"
 #include "swift/Basic/Defer.h"
 #include "swift/Basic/SourceManager.h"
@@ -50,6 +51,37 @@ static Expr *isImplicitPromotionToOptional(Expr *E) {
   return nullptr;
 }
 
+bool BaseDiagnosticWalker::walkToDeclPre(Decl *D) {
+  return isa<ClosureExpr>(D->getDeclContext())
+             ? shouldWalkIntoDeclInClosureContext(D)
+             : false;
+}
+
+bool BaseDiagnosticWalker::shouldWalkIntoDeclInClosureContext(Decl *D) {
+  auto *closure = dyn_cast<ClosureExpr>(D->getDeclContext());
+  assert(closure);
+
+  if (closure->isSeparatelyTypeChecked())
+    return false;
+
+  auto &opts = D->getASTContext().TypeCheckerOpts;
+
+  // If multi-statement inference is enabled, let's not walk
+  // into declarations contained in a multi-statement closure
+  // because they'd be handled via `typeCheckDecl` that runs
+  // syntactic diagnostics.
+  if (opts.EnableMultiStatementClosureInference &&
+      !closure->hasSingleExpressionBody()) {
+    // Since pattern bindings get their types through solution application,
+    // `typeCheckDecl` doesn't touch initializers (because they are already
+    // fully type-checked), so pattern bindings have to be allowed to be
+    // walked to diagnose syntactic issues.
+    return isa<PatternBindingDecl>(D);
+  }
+
+  return true;
+}
+
 /// Diagnose syntactic restrictions of expressions.
 ///
 ///   - Module values may only occur as part of qualification.
@@ -72,7 +104,7 @@ static Expr *isImplicitPromotionToOptional(Expr *E) {
 ///
 static void diagSyntacticUseRestrictions(const Expr *E, const DeclContext *DC,
                                          bool isExprStmt) {
-  class DiagnoseWalker : public ASTWalker {
+  class DiagnoseWalker : public BaseDiagnosticWalker {
     SmallPtrSet<Expr*, 4> AlreadyDiagnosedMetatypes;
     SmallPtrSet<DeclRefExpr*, 4> AlreadyDiagnosedBitCasts;
 
@@ -89,18 +121,8 @@ static void diagSyntacticUseRestrictions(const Expr *E, const DeclContext *DC,
       return { false, P };
     }
 
-    bool walkToDeclPre(Decl *D) override {
-      if (auto *closure = dyn_cast<ClosureExpr>(D->getDeclContext()))
-        return !closure->isSeparatelyTypeChecked();
-      return false;
-    }
-
     bool walkToTypeReprPre(TypeRepr *T) override { return true; }
 
-    bool shouldWalkIntoSeparatelyCheckedClosure(ClosureExpr *expr) override {
-      return false;
-    }
-
     bool shouldWalkCaptureInitializerExpressions() override { return true; }
 
     bool shouldWalkIntoTapExpression() override { return false; }
@@ -1449,7 +1471,7 @@ static void diagRecursivePropertyAccess(const Expr *E, const DeclContext *DC) {
 /// confusion, so we force an explicit self.
 static void diagnoseImplicitSelfUseInClosure(const Expr *E,
                                              const DeclContext *DC) {
-  class DiagnoseWalker : public ASTWalker {
+  class DiagnoseWalker : public BaseDiagnosticWalker {
     ASTContext &Ctx;
     SmallVector<AbstractClosureExpr *, 4> Closures;
   public:
@@ -1530,18 +1552,6 @@ static void diagnoseImplicitSelfUseInClosure(const Expr *E,
       return true;
     }
 
-
-    // Don't walk into nested decls.
-    bool walkToDeclPre(Decl *D) override {
-      if (auto *closure = dyn_cast<ClosureExpr>(D->getDeclContext()))
-        return !closure->isSeparatelyTypeChecked();
-      return false;
-    }
-
-    bool shouldWalkIntoSeparatelyCheckedClosure(ClosureExpr *expr) override {
-      return false;
-    }
-
     bool shouldWalkCaptureInitializerExpressions() override { return true; }
 
     bool shouldWalkIntoTapExpression() override { return false; }

lib/Sema/MiscDiagnostics.h

@@ -13,6 +13,7 @@
 #ifndef SWIFT_SEMA_MISC_DIAGNOSTICS_H
 #define SWIFT_SEMA_MISC_DIAGNOSTICS_H
 
+#include "swift/AST/ASTWalker.h"
 #include "swift/AST/AttrKind.h"
 #include "swift/AST/Pattern.h"
 #include "swift/AST/Expr.h"
@@ -26,7 +27,9 @@ namespace swift {
   class AbstractFunctionDecl;
   class ApplyExpr;
   class CallExpr;
+  class ClosureExpr;
   class DeclContext;
+  class Decl;
   class Expr;
   class InFlightDiagnostic;
   class Stmt;
@@ -122,6 +125,17 @@ void checkPatternBindingDeclAsyncUsage(PatternBindingDecl *decl);
 bool diagnoseUnhandledThrowsInAsyncContext(DeclContext *dc,
                                            ForEachStmt *forEach);
 
+class BaseDiagnosticWalker : public ASTWalker {
+  bool walkToDeclPre(Decl *D) override;
+
+  bool shouldWalkIntoSeparatelyCheckedClosure(ClosureExpr *expr) override {
+    return false;
+  }
+
+private:
+  static bool shouldWalkIntoDeclInClosureContext(Decl *D);
+};
+
 } // namespace swift
 
 #endif // SWIFT_SEMA_MISC_DIAGNOSTICS_H

lib/Sema/TypeCheckAvailability.cpp

@@ -3297,7 +3297,7 @@ void swift::diagnoseExprAvailability(const Expr *E, DeclContext *DC) {
 
 namespace {
 
-class StmtAvailabilityWalker : public ASTWalker {
+class StmtAvailabilityWalker : public BaseDiagnosticWalker {
   DeclContext *DC;
   bool WalkRecursively;
 
@@ -3333,7 +3333,6 @@ class StmtAvailabilityWalker : public ASTWalker {
     return std::make_pair(true, P);
   }
 };
-
 }
 
 void swift::diagnoseStmtAvailability(const Stmt *S, DeclContext *DC,