Fix exponential type checking of tuple literals.

This fixes two easy cases where we would go exponential in type
checking tuple literals.

Instead of generating a conversion to a single type variable (which
results in one large constraint system), we generate a conversion ot
the same type that appears in the initializer expression (which for
tuples is a tuple type, which naturally splits the constraint system).

I experimented with trying to generalize this further, but ran into
problems getting it working, so for now this will have to do.

Fixes rdar://problem/20233198.

lib/Sema/CSGen.cpp

@@ -1984,40 +1984,52 @@ namespace {
         // Var doesn't affect the type.
         return getTypeForPattern(cast<VarPattern>(pattern)->getSubPattern(),
                                  locator);
-      case PatternKind::Any:
-        // For a pattern of unknown type, create a new type variable.
+      case PatternKind::Any: {
+        // If we have a type from an initializer expression, and that
+        // expression does not produce an InOut type, use it.  This
+        // will avoid exponential typecheck behavior in the case of
+        // tuples, nested arrays, and dictionary literals.
+        //
+        // Otherwise, create a new type variable.
+        auto boundExpr = locator.trySimplifyToExpr();
+
+        if (boundExpr) {
+          auto boundExprTy = CS.getType(boundExpr);
+          if (!boundExprTy->is<InOutType>())
+            return boundExprTy->getRValueType();
+        }
+
         return CS.createTypeVariable(CS.getConstraintLocator(locator),
                                      TVO_CanBindToInOut);
+      }
 
       case PatternKind::Named: {
         auto var = cast<NamedPattern>(pattern)->getDecl();
-        
-        auto boundExpr = locator.trySimplifyToExpr();
-        auto haveBoundCollectionLiteral = boundExpr &&
-                                            !var->hasNonPatternBindingInit() &&
-                                            (isa<ArrayExpr>(boundExpr) ||
-                                             isa<DictionaryExpr>(boundExpr));
+        auto isWeak = false;
+        if (auto *OA = var->getAttrs().getAttribute<ReferenceOwnershipAttr>())
+          isWeak = OA->get() == ReferenceOwnership::Weak;
 
-        // For a named pattern without a type, create a new type variable
-        // and use it as the type of the variable.
+        auto boundExpr = locator.trySimplifyToExpr();
+        auto haveBoundExpr = boundExpr && !var->hasNonPatternBindingInit();
+
+        // If we have a type from an initializer expression, and that
+        // expression does not produce an InOut type, use it.  This
+        // will avoid exponential typecheck behavior in the case of
+        // tuples, nested arrays, and dictionary literals.
         //
-        // FIXME: For now, substitute in the bound type for literal collection
-        // exprs that would otherwise result in a simple conversion constraint
-        // being placed between two type variables. (The bound type and the
-        // collection type, which will always be the same in this case.)
-        // This will avoid exponential typecheck behavior in the case of nested
-        // array and dictionary literals.
-        Type ty = haveBoundCollectionLiteral ?
-                    CS.getType(boundExpr) :
-                    CS.createTypeVariable(CS.getConstraintLocator(locator),
-                                          TVO_CanBindToInOut);
+        // Otherwise, create a new type variable.
+        if (!isWeak && haveBoundExpr) {
+          auto boundExprTy = CS.getType(boundExpr);
+          if (!boundExprTy->is<InOutType>())
+            return boundExprTy->getRValueType();
+        }
+
+        Type ty = CS.createTypeVariable(CS.getConstraintLocator(locator),
+                                        TVO_CanBindToInOut);
 
         // For weak variables, use Optional<T>.
-        if (auto *OA = var->getAttrs().getAttribute<ReferenceOwnershipAttr>())
-          if (OA->get() == ReferenceOwnership::Weak) {
-            ty = CS.getTypeChecker().getOptionalType(var->getLoc(), ty);
-            if (!ty) return Type();
-          }
+        if (isWeak)
+          return CS.getTypeChecker().getOptionalType(var->getLoc(), ty);
 
         return ty;
       }

lib/Sema/TypeCheckConstraints.cpp

@@ -2131,7 +2131,9 @@ bool TypeChecker::typeCheckBinding(Pattern *&pattern, Expr *&initializer,
 
     Expr *foundSolution(Solution &solution, Expr *expr) override {
       // Figure out what type the constraints decided on.
-      InitTypeAndInOut.setPointer(solution.simplifyType(InitTypeAndInOut.getPointer()));
+      auto ty = solution.simplifyType(InitTypeAndInOut.getPointer());
+      InitTypeAndInOut.setPointer(
+          ty->getRValueType()->reconstituteSugar(/*recursive =*/false));
       InitTypeAndInOut.setInt(expr->isSemanticallyInOutExpr());
 
       // Just keep going.

test/APINotes/versioned.swift

@@ -118,11 +118,11 @@ func testAKA(structValue: ImportantCStruct, aliasValue: ImportantCAlias) {
 
   let optStructValue: Optional = structValue
   let _: Int = optStructValue
-  // CHECK-DIAGS-3: versioned.swift:[[@LINE-1]]:16: error: cannot convert value of type 'Optional<ImportantCStruct>' to specified type 'Int'
+  // CHECK-DIAGS-3: versioned.swift:[[@LINE-1]]:16: error: cannot convert value of type 'ImportantCStruct?' to specified type 'Int'
 
   let optAliasValue: Optional = aliasValue
   let _: Int = optAliasValue
-  // CHECK-DIAGS-3: versioned.swift:[[@LINE-1]]:16: error: cannot convert value of type 'Optional<ImportantCAlias>' (aka 'Optional<Int32>') to specified type 'Int'
+  // CHECK-DIAGS-3: versioned.swift:[[@LINE-1]]:16: error: cannot convert value of type 'ImportantCAlias?' (aka 'Optional<Int32>') to specified type 'Int'
 }
 
 func testRenamedEnumConstants() {

test/Constraints/array_literal.swift

@@ -129,7 +129,7 @@ func defaultToAny(i: Int, s: String) {
 
   let a2: Array = [1, "a", 3.5]
   // expected-error@-1{{heterogeneous collection literal could only be inferred to '[Any]'; add explicit type annotation if this is intentional}}
-  let _: Int = a2  // expected-error{{value of type 'Array<Any>'}}
+  let _: Int = a2  // expected-error{{value of type '[Any]'}}
   
   let a3 = [1, "a", nil, 3.5]
   // expected-error@-1{{heterogeneous collection literal could only be inferred to '[Any?]'; add explicit type annotation if this is intentional}}
@@ -137,7 +137,7 @@ func defaultToAny(i: Int, s: String) {
   
   let a4: Array = [1, "a", nil, 3.5]
   // expected-error@-1{{heterogeneous collection literal could only be inferred to '[Any?]'; add explicit type annotation if this is intentional}}
-  let _: Int = a4 // expected-error{{value of type 'Array<Any?>'}}
+  let _: Int = a4 // expected-error{{value of type '[Any?]'}}
 
   let a5 = []
   // expected-error@-1{{empty collection literal requires an explicit type}}

test/Constraints/bridging.swift

@@ -302,7 +302,7 @@ func rdar20029786(_ ns: NSString?) {
 
 // <rdar://problem/19813772> QoI: Using as! instead of as in this case produces really bad diagnostic
 func rdar19813772(_ nsma: NSMutableArray) {
-  var a1 = nsma as! Array // expected-error{{generic parameter 'Element' could not be inferred in cast to 'Array<_>'}} expected-note {{explicitly specify the generic arguments to fix this issue}} {{26-26=<Any>}}
+  var a1 = nsma as! Array // expected-error{{generic parameter 'Element' could not be inferred in cast to 'Array'}} expected-note {{explicitly specify the generic arguments to fix this issue}} {{26-26=<Any>}}
   var a2 = nsma as! Array<AnyObject> // expected-warning{{forced cast from 'NSMutableArray' to 'Array<AnyObject>' always succeeds; did you mean to use 'as'?}} {{17-20=as}}
   var a3 = nsma as Array<AnyObject>
 }

test/Constraints/patterns.swift

@@ -351,3 +351,16 @@ func testOne() {
     if case One.E.SomeError = error {} // expected-error{{generic enum type 'One.E' is ambiguous without explicit generic parameters when matching value of type 'Error'}}
   }
 }
+
+func overload(_ x: Int) -> Int { return x }
+func overload(_ x: Float) -> Float { return x }
+
+func rdar20233198() {
+  let typed: (Int, Int, Int, Int, Int, Int, Int, Int) = (Int(1), Int(1), Int(1), Int(1), Int(1), Int(1), Int(1), Int(1))
+  _ = typed
+  let _ = (Int(1), Int(1), Int(1), Int(1), Int(1), Int(1), Int(1), Int(1))
+  let named = (Int(1), Int(1), Int(1), Int(1), Int(1), Int(1), Int(1), Int(1))
+  _ = named;
+  let _ = (overload(1), overload(1), overload(1), overload(1), overload(1), overload(1), overload(1), overload(1))
+  let _ = (overload(1.0), overload(1.0), overload(1.0), overload(1.0), overload(1.0), overload(1.0), overload(1.0), overload(1.0))
+}

test/decl/var/variables.swift

@@ -82,7 +82,7 @@ func tuplePatternDestructuring(_ x : Int, y : Int) {
   _ = i+j
 
   // <rdar://problem/20395243> QoI: type variable reconstruction failing for tuple types
-  let (x: g1, a: h1) = (b: x, a: y)  // expected-error {{tuple type '(b: Int, a: Int)' is not convertible to tuple '(x: _, a: _)'}}
+  let (x: g1, a: h1) = (b: x, a: y)  // expected-error {{tuple type '(b: Int, a: Int)' is not convertible to tuple '(x: Int, a: Int)'}}
 }
 
 // <rdar://problem/21057425> Crash while compiling attached test-app.

validation-test/Sema/type_checker_perf/fast/rdar20233198.swift.gyb

@@ -1,4 +1,4 @@
-// RUN: %scale-test --invert-result --begin 1 --end 5 --step 1 --select incrementScopeCounter %s
+// RUN: %scale-test --begin 1 --end 5 --step 1 --select incrementScopeCounter %s
 // REQUIRES: OS=macosx
 // REQUIRES: asserts