Merge pull request #39989 from xedin/more-diag-improvements-for-multi-stmt-closures

[TypeChecker] SE-0326: Enable multi-statement closure inference by default

Author: xedin

include/swift/Basic/LangOptions.h

@@ -682,7 +682,7 @@ namespace swift {
 
     /// Enable experimental support for type inference through multi-statement
     /// closures.
-    bool EnableMultiStatementClosureInference = false;
+    bool EnableMultiStatementClosureInference = true;
 
     /// See \ref FrontendOptions.PrintFullConvention
     bool PrintFullConvention = false;

include/swift/Sema/CSBindings.h

@@ -338,6 +338,14 @@ class BindingSet {
 
   TypeVariableType *getTypeVariable() const { return Info.TypeVar; }
 
+  /// Check whether this binding set belongs to a type variable
+  /// that represents a result type of a closure.
+  bool forClosureResult() const;
+
+  /// Check whether this binding set belongs to a type variable
+  /// that represents a generic parameter.
+  bool forGenericParameter() const;
+
   bool canBeNil() const;
 
   /// If this type variable doesn't have any viable bindings, or

include/swift/Sema/CSFix.h

@@ -2282,6 +2282,10 @@ class SpecifyClosureParameterType final : public ConstraintFix {
 
   bool diagnose(const Solution &solution, bool asNote = false) const override;
 
+  bool diagnoseForAmbiguity(CommonFixesArray commonFixes) const override {
+    return diagnose(*commonFixes.front().first);
+  }
+
   static SpecifyClosureParameterType *create(ConstraintSystem &cs,
                                              ConstraintLocator *locator);
 

include/swift/Sema/Constraint.h

@@ -436,6 +436,8 @@ class Constraint final : public llvm::ilist_node<Constraint>,
       ASTNode Element;
       /// Contextual information associated with the element (if any).
       ContextualTypeInfo Context;
+      /// Identifies whether result of this node is unused.
+      bool IsDiscarded;
     } ClosureElement;
   };
 
@@ -489,7 +491,7 @@ class Constraint final : public llvm::ilist_node<Constraint>,
              SmallPtrSetImpl<TypeVariableType *> &typeVars);
 
   /// Construct a closure body element constraint.
-  Constraint(ASTNode node, ContextualTypeInfo context,
+  Constraint(ASTNode node, ContextualTypeInfo context, bool isDiscarded,
              ConstraintLocator *locator,
              SmallPtrSetImpl<TypeVariableType *> &typeVars);
 
@@ -579,12 +581,14 @@ class Constraint final : public llvm::ilist_node<Constraint>,
 
   static Constraint *createClosureBodyElement(ConstraintSystem &cs,
                                               ASTNode node,
-                                              ConstraintLocator *locator);
+                                              ConstraintLocator *locator,
+                                              bool isDiscarded = false);
 
   static Constraint *createClosureBodyElement(ConstraintSystem &cs,
                                               ASTNode node,
                                               ContextualTypeInfo context,
-                                              ConstraintLocator *locator);
+                                              ConstraintLocator *locator,
+                                              bool isDiscarded = false);
 
   /// Determine the kind of constraint.
   ConstraintKind getKind() const { return Kind; }
@@ -850,6 +854,11 @@ class Constraint final : public llvm::ilist_node<Constraint>,
     return ClosureElement.Context;
   }
 
+  bool isDiscardedElement() const {
+    assert(Kind == ConstraintKind::ClosureBodyElement);
+    return ClosureElement.IsDiscarded;
+  }
+
   /// For an applicable function constraint, retrieve the trailing closure
   /// matching rule.
   Optional<TrailingClosureMatching> getTrailingClosureMatching() const;

include/swift/Sema/ConstraintSystem.h

@@ -4845,8 +4845,8 @@ class ConstraintSystem {
   /// Simplify a closure body element constraint by generating required
   /// constraints to represent the given element in constraint system.
   SolutionKind simplifyClosureBodyElementConstraint(
-      ASTNode element, ContextualTypeInfo context, TypeMatchOptions flags,
-      ConstraintLocatorBuilder locator);
+      ASTNode element, ContextualTypeInfo context, bool isDiscarded,
+      TypeMatchOptions flags, ConstraintLocatorBuilder locator);
 
 public: // FIXME: Public for use by static functions.
   /// Simplify a conversion constraint with a fix applied to it.
@@ -5005,7 +5005,8 @@ class ConstraintSystem {
   /// \param replaceInvalidRefsWithErrors Indicates whether it's allowed
   /// to replace any discovered invalid member references with `ErrorExpr`.
   static bool preCheckExpression(Expr *&expr, DeclContext *dc,
-                                 bool replaceInvalidRefsWithErrors);
+                                 bool replaceInvalidRefsWithErrors,
+                                 bool leaveClosureBodiesUnchecked);
 
   /// Solve the system of constraints generated from provided target.
   ///
@@ -5236,6 +5237,16 @@ class ConstraintSystem {
   /// imported from C/ObjectiveC.
   bool isArgumentOfImportedDecl(ConstraintLocatorBuilder locator);
 
+  /// Check whether given closure should participate in inference e.g.
+  /// if it's a single-expression closure - it always does, but
+  /// multi-statement closures require special flags.
+  bool participatesInInference(ClosureExpr *closure) const;
+
+  /// Visit each subexpression that will be part of the constraint system
+  /// of the given expression, including those in closure bodies that will be
+  /// part of the constraint system.
+  void forEachExpr(Expr *expr, llvm::function_ref<Expr *(Expr *)> callback);
+
   SWIFT_DEBUG_DUMP;
   SWIFT_DEBUG_DUMPER(dump(Expr *));
 
@@ -6059,18 +6070,6 @@ BraceStmt *applyResultBuilderTransform(
           constraints::SolutionApplicationTarget)>
             rewriteTarget);
 
-/// Determine whether the given closure expression should be type-checked
-/// within the context of its enclosing expression. Otherwise, it will be
-/// separately type-checked once its enclosing expression has determined all
-/// of the parameter and result types without looking at the body.
-bool shouldTypeCheckInEnclosingExpression(ClosureExpr *expr);
-
-/// Visit each subexpression that will be part of the constraint system
-/// of the given expression, including those in closure bodies that will be
-/// part of the constraint system.
-void forEachExprInConstraintSystem(
-    Expr *expr, llvm::function_ref<Expr *(Expr *)> callback);
-
 /// Whether the given parameter requires an argument.
 bool parameterRequiresArgument(
     ArrayRef<AnyFunctionType::Param> params,

include/swift/Sema/IDETypeChecking.h

@@ -47,7 +47,8 @@ namespace swift {
   struct PrintOptions;
 
   /// Typecheck binding initializer at \p bindingIndex.
-  void typeCheckPatternBinding(PatternBindingDecl *PBD, unsigned bindingIndex);
+  void typeCheckPatternBinding(PatternBindingDecl *PBD, unsigned bindingIndex,
+                               bool leaveClosureBodiesUnchecked);
 
   /// Check if T1 is convertible to T2.
   ///

lib/IDE/ExprContextAnalysis.cpp

@@ -98,7 +98,8 @@ void swift::ide::typeCheckContextAt(DeclContext *DC, SourceLoc Loc) {
             [](VarDecl *VD) { (void)VD->getInterfaceType(); });
         if (PBD->getInit(i)) {
           if (!PBD->isInitializerChecked(i))
-            typeCheckPatternBinding(PBD, i);
+            typeCheckPatternBinding(PBD, i,
+                                    /*LeaveClosureBodyUnchecked=*/true);
         }
       }
     } else if (auto *defaultArg = dyn_cast<DefaultArgumentInitializer>(DC)) {

lib/Sema/BuilderTransform.cpp

@@ -1932,7 +1932,9 @@ class PreCheckResultBuilderApplication : public ASTWalker {
       DiagnosticTransaction transaction(diagEngine);
 
       HasError |= ConstraintSystem::preCheckExpression(
-          E, DC, /*replaceInvalidRefsWithErrors=*/true);
+          E, DC, /*replaceInvalidRefsWithErrors=*/true,
+          /*leaveClosureBodiesUnchecked=*/false);
+
       HasError |= transaction.hasErrors();
 
       if (!HasError)

lib/Sema/CSApply.cpp

@@ -4056,8 +4056,7 @@ namespace {
       if (expr->isLiteralInit()) {
         auto *literalInit = expr->getSubExpr();
         if (auto *call = dyn_cast<CallExpr>(literalInit)) {
-          forEachExprInConstraintSystem(call->getFn(),
-                                        [&](Expr *subExpr) -> Expr * {
+          cs.forEachExpr(call->getFn(), [&](Expr *subExpr) -> Expr * {
             auto *TE = dyn_cast<TypeExpr>(subExpr);
             if (!TE)
               return subExpr;

lib/Sema/CSBindings.cpp

@@ -25,6 +25,14 @@ using namespace swift;
 using namespace constraints;
 using namespace inference;
 
+bool BindingSet::forClosureResult() const {
+  return Info.TypeVar->getImpl().isClosureResultType();
+}
+
+bool BindingSet::forGenericParameter() const {
+  return bool(Info.TypeVar->getImpl().getGenericParameter());
+}
+
 bool BindingSet::canBeNil() const {
   auto &ctx = CS.getASTContext();
   return Literals.count(