[CS] Unify ReturnStmt handling

Unify the implementation between single-expression
and multi-statement closures. Because we're now
storing a contextual type for single expression
closure returns, update a code completion test to
bring its behavior inline with the multi-statement
case.

Author: hamishknight

include/swift/Sema/SyntacticElementTarget.h

@@ -431,6 +431,11 @@ class SyntacticElementTarget {
     expression.contextualInfo.typeLoc = type;
   }
 
+  void setExprContextualTypePurpose(ContextualTypePurpose ctp) {
+    assert(kind == Kind::expression);
+    expression.contextualInfo.purpose = ctp;
+  }
+
   /// Whether this target is for an initialization expression and pattern.
   bool isForInitialization() const {
     return kind == Kind::expression &&

lib/Sema/CSApply.cpp

@@ -9595,22 +9595,8 @@ ExprWalker::rewriteTarget(SyntacticElementTarget target) {
 
       auto *locator = target.getExprConvertTypeLocator();
       if (!locator) {
-        // Bodies of single-expression closures use a special locator
-        // for contextual type conversion to make sure that result is
-        // convertible to `Void` when `return` is not used explicitly.
-        auto *closure = dyn_cast<ClosureExpr>(target.getDeclContext());
-        if (closure && closure->hasSingleExpressionBody() &&
-            contextualTypePurpose == CTP_ClosureResult) {
-          auto *returnStmt =
-              castToStmt<ReturnStmt>(closure->getBody()->getLastElement());
-
-          locator = cs.getConstraintLocator(
-              closure, LocatorPathElt::ClosureBody(
-                           /*hasImpliedReturn*/ returnStmt->isImplied()));
-        } else {
-          locator = cs.getConstraintLocator(
-              expr, LocatorPathElt::ContextualType(contextualTypePurpose));
-        }
+        locator = cs.getConstraintLocator(
+            expr, LocatorPathElt::ContextualType(contextualTypePurpose));
       }
       assert(locator);
 

lib/Sema/CSSyntacticElement.cpp

@@ -1242,32 +1242,7 @@ class SyntacticElementConstraintGenerator
   }
 
   void visitReturnStmt(ReturnStmt *returnStmt) {
-    // Single-expression closures are effectively a `return` statement,
-    // so let's give them a special locator as to indicate that.
-    // Return statements might not have a result if we have a closure whose
-    // implicit returned value is coerced to Void.
-    if (context.isSingleExpressionClosure(cs) && returnStmt->hasResult()) {
-      auto *expr = returnStmt->getResult();
-      assert(expr && "single expression closure without expression?");
-
-      expr = cs.generateConstraints(expr, context.getAsDeclContext());
-      if (!expr) {
-        hadError = true;
-        return;
-      }
-
-      auto contextualResultInfo = getContextualResultInfo();
-      cs.addConstraint(ConstraintKind::Conversion, cs.getType(expr),
-                       contextualResultInfo.getType(),
-                       cs.getConstraintLocator(
-                           context.getAsAbstractClosureExpr().get(),
-                           LocatorPathElt::ClosureBody(
-                               /*hasImpliedReturn=*/returnStmt->isImplied())));
-      return;
-    }
-
     Expr *resultExpr;
-
     if (returnStmt->hasResult()) {
       resultExpr = returnStmt->getResult();
       assert(resultExpr && "non-empty result without expression?");
@@ -1280,9 +1255,18 @@ class SyntacticElementConstraintGenerator
     }
 
     auto contextualResultInfo = getContextualResultInfo();
+
+    // Single-expression closures need their contextual type locator anchored
+    // on the closure itself.
+    if (context.isSingleExpressionClosure(cs) && returnStmt->hasResult()) {
+      contextualResultInfo.locator = cs.getConstraintLocator(
+          context.getAsAbstractClosureExpr().get(),
+          {LocatorPathElt::ClosureBody(
+              /*hasImpliedReturn=*/returnStmt->isImplied())});
+    }
+
     SyntacticElementTarget target(resultExpr, context.getAsDeclContext(),
-                                  contextualResultInfo,
-                                  /*isDiscarded=*/false);
+                                  contextualResultInfo, /*isDiscarded=*/false);
 
     if (cs.generateConstraints(target)) {
       hadError = true;
@@ -2155,22 +2139,15 @@ class SyntacticElementSolutionApplication
       mode = convertToResult;
     }
 
-    llvm::Optional<SyntacticElementTarget> resultTarget;
-    if (auto target = cs.getTargetFor(returnStmt)) {
-      resultTarget = *target;
-    } else {
-      // Single-expression closures have to handle returns in a special
-      // way so the target has to be created for them during solution
-      // application based on the resolved type.
-      assert(context.isSingleExpressionClosure(cs));
-      resultTarget = SyntacticElementTarget(
-          resultExpr, context.getAsDeclContext(),
-          mode == convertToResult ? CTP_ClosureResult : CTP_Unused,
-          mode == convertToResult ? resultType : Type(),
-          /*isDiscarded=*/false);
-    }
-
-    if (auto newResultTarget = rewriteTarget(*resultTarget)) {
+    auto target = *cs.getTargetFor(returnStmt);
+
+    // If we're not converting to a result, unset the contextual type.
+    if (mode != convertToResult) {
+      target.setExprConversionType(Type());
+      target.setExprContextualTypePurpose(CTP_Unused);
+    }
+
+    if (auto newResultTarget = rewriteTarget(target)) {
       resultExpr = newResultTarget->getAsExpr();
     }
 

test/IDE/complete_single_expression_return.swift

@@ -155,10 +155,27 @@ struct TestExplicitSingleExprClosureBinding {
       return self.#^TestExplicitSingleExprClosureBinding^#
     }
   }
-// FIXME: Because we have an explicit return, and no expected type, we shouldn't suggest Void.
+// We have an explicit return, and no expected type, so we don't suggest Void.
 // TestExplicitSingleExprClosureBinding-DAG: Decl[InstanceMethod]/CurrNominal: str()[#String#];
 // TestExplicitSingleExprClosureBinding-DAG: Decl[InstanceMethod]/CurrNominal: int()[#Int#];
-// TestExplicitSingleExprClosureBinding-DAG: Decl[InstanceMethod]/CurrNominal: void()[#Void#];
+// TestExplicitSingleExprClosureBinding-DAG: Decl[InstanceMethod]/CurrNominal/TypeRelation[Invalid]: void()[#Void#];
+}
+
+struct TestExplicitMultiStmtClosureBinding {
+  func void() -> Void {}
+  func str() -> String { return "" }
+  func int() -> Int { return 0 }
+
+  func test() {
+    let fn = {
+      ()
+      return self.#^TestExplicitMultiStmtClosureBinding^#
+    }
+  }
+// We have an explicit return, and no expected type, so we don't suggest Void.
+// TestExplicitMultiStmtClosureBinding-DAG: Decl[InstanceMethod]/CurrNominal: str()[#String#];
+// TestExplicitMultiStmtClosureBinding-DAG: Decl[InstanceMethod]/CurrNominal: int()[#Int#];
+// TestExplicitMultiStmtClosureBinding-DAG: Decl[InstanceMethod]/CurrNominal/TypeRelation[Invalid]: void()[#Void#];
 }
 
 struct TestExplicitSingleExprClosureBindingWithContext {