Merge pull request swiftlang#68207 from hamishknight/nestless

Author: hamishknight

lib/AST/Expr.cpp

@@ -2519,30 +2519,47 @@ SingleValueStmtExpr *SingleValueStmtExpr::createWithWrappedBranches(
 
 SingleValueStmtExpr *
 SingleValueStmtExpr::tryDigOutSingleValueStmtExpr(Expr *E) {
-  while (true) {
-    // Look through implicit conversions.
-    if (auto *ICE = dyn_cast<ImplicitConversionExpr>(E)) {
-      E = ICE->getSubExpr();
-      continue;
+  class SVEFinder final : public ASTWalker {
+  public:
+    SingleValueStmtExpr *FoundSVE = nullptr;
+
+    PreWalkResult<Expr *> walkToExprPre(Expr *E) override {
+      if (auto *SVE = dyn_cast<SingleValueStmtExpr>(E)) {
+        FoundSVE = SVE;
+        return Action::Stop();
+      }
+
+      // Look through implicit exprs.
+      if (E->isImplicit())
+        return Action::Continue(E);
+
+      // Look through coercions.
+      if (isa<CoerceExpr>(E))
+        return Action::Continue(E);
+
+      // Look through try/await (this is invalid, but we'll error on it in
+      // effect checking).
+      if (isa<AnyTryExpr>(E) || isa<AwaitExpr>(E))
+        return Action::Continue(E);
+
+      return Action::Stop();
     }
-    // Look through coercions.
-    if (auto *CE = dyn_cast<CoerceExpr>(E)) {
-      E = CE->getSubExpr();
-      continue;
+    PreWalkResult<Stmt *> walkToStmtPre(Stmt *S) override {
+      return Action::Stop();
     }
-    // Look through try/await (this is invalid, but we'll error on it in
-    // effect checking).
-    if (auto *TE = dyn_cast<AnyTryExpr>(E)) {
-      E = TE->getSubExpr();
-      continue;
+    PreWalkAction walkToDeclPre(Decl *D) override {
+      return Action::Stop();
     }
-    if (auto *AE = dyn_cast<AwaitExpr>(E)) {
-      E = AE->getSubExpr();
-      continue;
+    PreWalkResult<Pattern *> walkToPatternPre(Pattern *P) override {
+      return Action::Stop();
     }
-    break;
-  }
-  return dyn_cast<SingleValueStmtExpr>(E);
+    PreWalkAction walkToTypeReprPre(TypeRepr *T) override {
+      return Action::Stop();
+    }
+  };
+  SVEFinder finder;
+  E->walk(finder);
+  return finder.FoundSVE;
 }
 
 SourceRange SingleValueStmtExpr::getSourceRange() const {

lib/Sema/MiscDiagnostics.cpp

@@ -3848,7 +3848,20 @@ class SingleValueStmtUsageChecker final : public ASTWalker {
   llvm::DenseSet<SingleValueStmtExpr *> ValidSingleValueStmtExprs;
 
 public:
-  SingleValueStmtUsageChecker(ASTContext &ctx) : Ctx(ctx), Diags(ctx.Diags) {}
+  SingleValueStmtUsageChecker(
+      ASTContext &ctx, ASTNode root,
+      llvm::Optional<ContextualTypePurpose> contextualPurpose)
+      : Ctx(ctx), Diags(ctx.Diags) {
+    assert(!root.is<Expr *>() || contextualPurpose &&
+           "Must provide contextual purpose for expr");
+
+    // If we have a contextual purpose, this is for an expression. Check if it's
+    // an expression in a valid position.
+    if (contextualPurpose) {
+      markAnyValidTopLevelSingleValueStmt(root.get<Expr *>(),
+                                          *contextualPurpose);
+    }
+  }
 
 private:
   /// Mark a given expression as a valid position for a SingleValueStmtExpr.
@@ -3860,8 +3873,23 @@ class SingleValueStmtUsageChecker final : public ASTWalker {
       ValidSingleValueStmtExprs.insert(SVE);
   }
 
+  /// Mark a valid top-level expression with a given contextual purpose.
+  void markAnyValidTopLevelSingleValueStmt(Expr *E, ContextualTypePurpose ctp) {
+    // Allowed in returns, throws, and bindings.
+    switch (ctp) {
+    case CTP_ReturnStmt:
+    case CTP_ReturnSingleExpr:
+    case CTP_ThrowStmt:
+    case CTP_Initialization:
+      markValidSingleValueStmt(E);
+      break;
+    default:
+      break;
+    }
+  }
+
   MacroWalking getMacroWalkingBehavior() const override {
-    return MacroWalking::Expansion;
+    return MacroWalking::ArgumentsAndExpansion;
   }
 
   AssignExpr *findAssignment(Expr *E) const {
@@ -3987,28 +4015,33 @@ class SingleValueStmtUsageChecker final : public ASTWalker {
     if (auto *PBD = dyn_cast<PatternBindingDecl>(D)) {
       for (auto idx : range(PBD->getNumPatternEntries()))
         markValidSingleValueStmt(PBD->getInit(idx));
+
+      return Action::Continue();
     }
-    // Valid as a single expression body of a function. This is needed in
-    // addition to ReturnStmt checking, as we will remove the return if the
-    // expression is inferred to be Never.
-    if (auto *AFD = dyn_cast<AbstractFunctionDecl>(D)) {
-      if (AFD->hasSingleExpressionBody())
-        markValidSingleValueStmt(AFD->getSingleExpressionBody());
-    }
-    return Action::Continue();
+    // We don't want to walk into any other decl, we will visit them as part of
+    // typeCheckDecl.
+    return Action::SkipChildren();
   }
 };
 } // end anonymous namespace
 
+void swift::diagnoseOutOfPlaceExprs(
+    ASTContext &ctx, ASTNode root,
+    llvm::Optional<ContextualTypePurpose> contextualPurpose) {
+  // TODO: We ought to consider moving this into pre-checking such that we can
+  // still diagnose on invalid code, and don't have to traverse over implicit
+  // exprs. We need to first separate out SequenceExpr folding though.
+  SingleValueStmtUsageChecker sveChecker(ctx, root, contextualPurpose);
+  root.walk(sveChecker);
+}
+
 /// Apply the warnings managed by VarDeclUsageChecker to the top level
 /// code declarations that haven't been checked yet.
 void swift::
 performTopLevelDeclDiagnostics(TopLevelCodeDecl *TLCD) {
   auto &ctx = TLCD->getDeclContext()->getASTContext();
   VarDeclUsageChecker checker(TLCD, ctx.Diags);
   TLCD->walk(checker);
-  SingleValueStmtUsageChecker sveChecker(ctx);
-  TLCD->walk(sveChecker);
 }
 
 /// Perform diagnostics for func/init/deinit declarations.
@@ -4024,10 +4057,6 @@ void swift::performAbstractFuncDeclDiagnostics(AbstractFunctionDecl *AFD) {
     auto &ctx = AFD->getDeclContext()->getASTContext();
     VarDeclUsageChecker checker(AFD, ctx.Diags);
     AFD->walk(checker);
-
-    // Do a similar walk to check for out of place SingleValueStmtExprs.
-    SingleValueStmtUsageChecker sveChecker(ctx);
-    AFD->walk(sveChecker);
   }
 
   auto *body = AFD->getBody();
@@ -5849,10 +5878,10 @@ diagnoseDictionaryLiteralDuplicateKeyEntries(const Expr *E,
 //===----------------------------------------------------------------------===//
 
 /// Emit diagnostics for syntactic restrictions on a given expression.
-void swift::performSyntacticExprDiagnostics(const Expr *E,
-                                            const DeclContext *DC,
-                                            bool isExprStmt,
-                                            bool disableExprAvailabilityChecking) {
+void swift::performSyntacticExprDiagnostics(
+    const Expr *E, const DeclContext *DC,
+    llvm::Optional<ContextualTypePurpose> contextualPurpose, bool isExprStmt,
+    bool disableExprAvailabilityChecking, bool disableOutOfPlaceExprChecking) {
   auto &ctx = DC->getASTContext();
   TypeChecker::diagnoseSelfAssignment(E);
   diagSyntacticUseRestrictions(E, DC, isExprStmt);
@@ -5871,6 +5900,8 @@ void swift::performSyntacticExprDiagnostics(const Expr *E,
   diagnoseConstantArgumentRequirement(E, DC);
   diagUnqualifiedAccessToMethodNamedSelf(E, DC);
   diagnoseDictionaryLiteralDuplicateKeyEntries(E, DC);
+  if (!disableOutOfPlaceExprChecking)
+    diagnoseOutOfPlaceExprs(ctx, const_cast<Expr *>(E), contextualPurpose);
 }
 
 void swift::performStmtDiagnostics(const Stmt *S, DeclContext *DC) {

lib/Sema/MiscDiagnostics.h

@@ -28,6 +28,7 @@ namespace swift {
   class ApplyExpr;
   class CallExpr;
   class ClosureExpr;
+  enum ContextualTypePurpose : uint8_t;
   class DeclContext;
   class Decl;
   class Expr;
@@ -37,10 +38,22 @@ namespace swift {
   class ValueDecl;
   class ForEachStmt;
 
+/// Diagnose any expressions that appear in an unsupported position. If visiting
+/// an expression directly, its \p contextualPurpose should be provided to
+/// evaluate its position.
+void diagnoseOutOfPlaceExprs(
+    ASTContext &ctx, ASTNode root,
+    llvm::Optional<ContextualTypePurpose> contextualPurpose);
+
 /// Emit diagnostics for syntactic restrictions on a given expression.
+///
+/// Note: \p contextualPurpose must be non-nil, unless
+/// \p disableOutOfPlaceExprChecking is set to \c true.
 void performSyntacticExprDiagnostics(
     const Expr *E, const DeclContext *DC,
-    bool isExprStmt, bool disableExprAvailabilityChecking = false);
+    llvm::Optional<ContextualTypePurpose> contextualPurpose,
+    bool isExprStmt, bool disableExprAvailabilityChecking = false,
+    bool disableOutOfPlaceExprChecking = false);
 
 /// Emit diagnostics for a given statement.
 void performStmtDiagnostics(const Stmt *S, DeclContext *DC);

lib/Sema/TypeCheckConstraints.cpp

@@ -307,7 +307,11 @@ class FunctionSyntacticDiagnosticWalker : public ASTWalker {
   }
 
   PreWalkResult<Expr *> walkToExprPre(Expr *expr) override {
-    performSyntacticExprDiagnostics(expr, dcStack.back(), /*isExprStmt=*/false);
+    // We skip out-of-place expr checking here since we've already performed it.
+    performSyntacticExprDiagnostics(expr, dcStack.back(), /*ctp*/ llvm::None,
+                                    /*isExprStmt=*/false,
+                                    /*disableAvailabilityChecking*/ false,
+                                    /*disableOutOfPlaceExprChecking*/ true);
 
     if (auto closure = dyn_cast<ClosureExpr>(expr)) {
       if (closure->isSeparatelyTypeChecked()) {
@@ -354,8 +358,9 @@ void constraints::performSyntacticDiagnosticsForTarget(
   switch (target.kind) {
   case SyntacticElementTarget::Kind::expression: {
     // First emit diagnostics for the main expression.
-    performSyntacticExprDiagnostics(target.getAsExpr(), dc,
-                                    isExprStmt, disableExprAvailabilityChecking);
+    performSyntacticExprDiagnostics(
+        target.getAsExpr(), dc, target.getExprContextualTypePurpose(),
+        isExprStmt, disableExprAvailabilityChecking);
     return;
   }
 
@@ -364,17 +369,25 @@ void constraints::performSyntacticDiagnosticsForTarget(
 
     // First emit diagnostics for the main expression.
     performSyntacticExprDiagnostics(stmt->getTypeCheckedSequence(), dc,
-                                    isExprStmt,
+                                    CTP_ForEachSequence, isExprStmt,
                                     disableExprAvailabilityChecking);
 
     if (auto *whereExpr = stmt->getWhere())
-      performSyntacticExprDiagnostics(whereExpr, dc, /*isExprStmt*/ false);
+      performSyntacticExprDiagnostics(whereExpr, dc, CTP_Condition,
+                                      /*isExprStmt*/ false);
     return;
   }
 
   case SyntacticElementTarget::Kind::function: {
+    // Check for out of place expressions. This needs to be done on the entire
+    // function body rather than on individual expressions since we need the
+    // context of the parent nodes.
+    auto *body = target.getFunctionBody();
+    diagnoseOutOfPlaceExprs(dc->getASTContext(), body,
+                            /*contextualPurpose*/ llvm::None);
+
     FunctionSyntacticDiagnosticWalker walker(dc);
-    target.getFunctionBody()->walk(walker);
+    body->walk(walker);
     return;
   }
   case SyntacticElementTarget::Kind::closure:

test/Constraints/closures.swift

@@ -1152,11 +1152,9 @@ struct R_76250381<Result, Failure: Error> {
 // rdar://77022842 - crash due to a missing argument to a ternary operator
 func rdar77022842(argA: Bool? = nil, argB: Bool? = nil) {
   if let a = argA ?? false, if let b = argB ?? {
-    // expected-error@-1 {{'if' may only be used as expression in return, throw, or as the source of an assignment}}
-    // expected-error@-2 {{initializer for conditional binding must have Optional type, not 'Bool'}}
-    // expected-error@-3 {{cannot convert value of type '() -> ()' to expected argument type 'Bool?'}}
-    // expected-error@-4 {{cannot convert value of type 'Void' to expected condition type 'Bool'}}
-    // expected-error@-5 {{'if' must have an unconditional 'else' to be used as expression}}
+    // expected-error@-1 {{initializer for conditional binding must have Optional type, not 'Bool'}}
+    // expected-error@-2 {{cannot convert value of type '() -> ()' to expected argument type 'Bool?'}}
+    // expected-error@-3 {{cannot convert value of type 'Void' to expected condition type 'Bool'}}
   } // expected-error {{expected '{' after 'if' condition}}
 }
 

test/Constraints/if_expr.swift

@@ -387,7 +387,6 @@ func testReturnMismatch() {
   let _ = if .random() {
     return 1 // expected-error {{unexpected non-void return value in void function}}
     // expected-note@-1 {{did you mean to add a return type?}}
-    // expected-error@-2 {{cannot 'return' in 'if' when used as expression}}
   } else {
     0
   }
@@ -651,9 +650,46 @@ func builderWithBinding() -> Either<String, Int> {
   }
 }
 
+@Builder
+func builderWithInvalidBinding() -> Either<String, Int> {
+  let str = (if .random() { "a" } else { "b" })
+  // expected-error@-1 {{'if' may only be used as expression in return, throw, or as the source of an assignment}}
+  if .random() {
+    str
+  } else {
+    1
+  }
+}
+
+func takesBuilder(@Builder _ fn: () -> Either<String, Int>) {}
+
+func builderClosureWithBinding() {
+  takesBuilder {
+    // Make sure the binding gets type-checked as an if expression, but the
+    // other if block gets type-checked as a stmt.
+    let str = if .random() { "a" } else { "b" }
+    if .random() {
+      str
+    } else {
+      1
+    }
+  }
+}
+
+func builderClosureWithInvalidBinding()  {
+  takesBuilder {
+    let str = (if .random() { "a" } else { "b" })
+    // expected-error@-1 {{'if' may only be used as expression in return, throw, or as the source of an assignment}}
+    if .random() {
+      str
+    } else {
+      1
+    }
+  }
+}
+
 func builderInClosure() {
-  func build(@Builder _ fn: () -> Either<String, Int>) {}
-  build {
+  takesBuilder {
     if .random() {
       ""
     } else {