[Sema] Implement SE-0110

This commit built upon the work of Pull Request 3895. Apart from the
work to make the following work

```swift
let f: (Int, Int) -> Void = { x in  } // this is now an error
```

This patch also implement the part 2 mentioned in the #3895

```swift
let g: ((Int, Int)) -> Void = { y in  } // y should have type (Int, Int)
```

Author: MnO2

include/swift/AST/DiagnosticsSema.def

@@ -2489,7 +2489,10 @@ ERROR(tuple_pattern_in_non_tuple_context,none,
       "tuple pattern cannot match values of the non-tuple type %0", (Type))
 ERROR(closure_argument_list_tuple,none,
       "contextual closure type %0 expects %1 argument%s1, "
-      "but %2 were used in closure body", (Type, unsigned, unsigned))
+      "but %2 %select{were|was}3 used in closure body", (Type, unsigned, unsigned, bool))
+ERROR(closure_argument_list_single_tuple,none,
+      "contextual closure type specifies %0, but %1 %select{was|were}2 used in closure body, "
+      "try adding extra parentheses around the single tuple argument", (Type, unsigned, bool))
 ERROR(closure_argument_list_missing,none,
       "contextual type for closure argument list expects %0 argument%s0, "
       "which cannot be implicitly ignored", (unsigned))

lib/Sema/CSApply.cpp

@@ -6464,7 +6464,7 @@ namespace {
         // Coerce the pattern, in case we resolved something.
         auto fnType = closure->getType()->castTo<FunctionType>();
         auto *params = closure->getParameters();
-        if (tc.coerceParameterListToType(params, closure, fnType->getInput()))
+        if (tc.coerceParameterListToType(params, closure, fnType))
           return { false, nullptr };
 
         // If this is a single-expression closure, convert the expression

lib/Sema/CSDiag.cpp

@@ -5614,11 +5614,11 @@ bool FailureDiagnosis::visitClosureExpr(ClosureExpr *CE) {
       // don't confuse the issue.
       fnType = FunctionType::get(fnType->getInput(), fnType->getResult());
       diagnose(params->getStartLoc(), diag::closure_argument_list_tuple,
-               fnType, inferredArgCount, actualArgCount);
+               fnType, inferredArgCount, actualArgCount, (actualArgCount == 1));
       return true;
     }
 
-    if (CS->TC.coerceParameterListToType(params, CE, inferredArgType))
+    if (CS->TC.coerceParameterListToType(params, CE, fnType))
       return true;
 
     expectedResultType = fnType->getResult();

lib/Sema/TypeCheckConstraints.cpp

@@ -1523,6 +1523,24 @@ bool TypeChecker::typeCheckExpression(Expr *&expr, DeclContext *dc,
          convertType.getType()->hasUnresolvedType())) {
       convertType = TypeLoc();
       convertTypePurpose = CTP_Unused;
+    } else if (auto closure = dyn_cast<ClosureExpr>(expr)) {
+      auto *P = closure->getParameters();
+      
+      if (P->size() == 1 && convertType.getType()->is<FunctionType>()) {
+        auto hintFnType = convertType.getType()->castTo<FunctionType>();
+        auto hintFnInputType = hintFnType->getInput();
+        
+        // Cannot use hintFnInputType->is<TupleType>() since it would desugar ParenType
+        if (isa<TupleType>(hintFnInputType.getPointer())) {
+          TupleType *tupleTy = hintFnInputType->castTo<TupleType>();
+          
+          if (tupleTy->getNumElements() >= 2) {
+            diagnose(P->getStartLoc(), diag::closure_argument_list_single_tuple,
+                     hintFnInputType, P->size(), P->size() > 1);
+            return true;
+          }
+        }
+      }
     }
   }
 

lib/Sema/TypeCheckPattern.cpp

@@ -1526,8 +1526,9 @@ bool TypeChecker::coercePatternToType(Pattern *&P, DeclContext *dc, Type type,
 /// TODO: These diagnostics should be a lot better now that we know this is
 /// all specific to closures.
 ///
-bool TypeChecker::coerceParameterListToType(ParameterList *P, DeclContext *DC,
-                                            Type paramListType) {
+bool TypeChecker::coerceParameterListToType(ParameterList *P, ClosureExpr *CE,
+                                            AnyFunctionType *FN) {
+  Type paramListType = FN->getInput();
   bool hadError = paramListType->is<ErrorType>();
 
   // Sometimes a scalar type gets applied to a single-argument parameter list.
@@ -1536,7 +1537,7 @@ bool TypeChecker::coerceParameterListToType(ParameterList *P, DeclContext *DC,
 
     // Check that the type, if explicitly spelled, is ok.
     if (param->getTypeLoc().getTypeRepr()) {
-      hadError |= validateParameterType(param, DC, TypeResolutionOptions(),
+      hadError |= validateParameterType(param, CE, TypeResolutionOptions(),
                                         nullptr, *this);
 
       // Now that we've type checked the explicit argument type, see if it
@@ -1564,6 +1565,22 @@ bool TypeChecker::coerceParameterListToType(ParameterList *P, DeclContext *DC,
     return hadError;
   };
 
+  // Check if paramListType only contains one single tuple.
+  // If it is, then paramListType would be sugared ParenType
+  // with a single underlying TupleType. In that case, check if
+  // the closure argument is also one to avoid the tuple splat
+  // from happening.
+  if (!hadError && isa<ParenType>(paramListType.getPointer())) {
+    auto underlyingTy = paramListType->getCanonicalType();
+    
+    if (underlyingTy->is<TupleType>()) {
+      if (P->size() == 1) {
+        return handleParameter(P->get(0), underlyingTy);
+      }
+    }
+    
+    //pass
+  }
 
   // The context type must be a tuple.
   TupleType *tupleTy = paramListType->getAs<TupleType>();
@@ -1578,11 +1595,9 @@ bool TypeChecker::coerceParameterListToType(ParameterList *P, DeclContext *DC,
   // The number of elements must match exactly.
   // TODO: incomplete tuple patterns, with some syntax.
   if (!hadError && tupleTy->getNumElements() != P->size()) {
-    if (P->size() == 1)
-      return handleParameter(P->get(0), paramListType);
-    
-    diagnose(P->getStartLoc(), diag::tuple_pattern_length_mismatch,
-             paramListType);
+    auto fnType = FunctionType::get(paramListType->getDesugaredType(), FN->getResult());
+    diagnose(P->getStartLoc(), diag::closure_argument_list_tuple,
+             fnType, tupleTy->getNumElements(), P->size(), (P->size() == 1));
     hadError = true;
   }
 

lib/Sema/TypeChecker.h

@@ -1404,7 +1404,7 @@ class TypeChecker final : public LazyResolver {
   /// contextual type.
   ///
   /// \returns true if an error occurred, false otherwise.
-  bool coerceParameterListToType(ParameterList *P, DeclContext *dc, Type type);
+  bool coerceParameterListToType(ParameterList *P, ClosureExpr *CE, AnyFunctionType *FN);
 
 
   /// Type-check an initialized variable pattern declaration.

test/Constraints/closures.swift

@@ -8,7 +8,7 @@ _ = myMap(intArray, { String($0) })
 _ = myMap(intArray, { x -> String in String(x) } )
 
 // Closures with too few parameters.
-func foo(_ x: (Int, Int) -> Int) {}
+func foo(_ x: ((Int, Int)) -> Int) {}
 foo({$0}) // expected-error{{cannot convert value of type '(Int, Int)' to closure result type 'Int'}}
 
 struct X {}
@@ -130,7 +130,7 @@ var _: (Int) -> Int = {a,b in 0}
 // expected-error @+1 {{contextual closure type '(Int) -> Int' expects 1 argument, but 3 were used in closure body}}
 var _: (Int) -> Int = {a,b,c in 0}
 
-var _: (Int, Int) -> Int = {a in 0}
+var _: ((Int, Int)) -> Int = {a in 0}
 
 // expected-error @+1 {{contextual closure type '(Int, Int, Int) -> Int' expects 3 arguments, but 2 were used in closure body}}
 var _: (Int, Int, Int) -> Int = {a, b in a+b}
@@ -202,7 +202,7 @@ func acceptNothingToInt (_: () -> Int) {}
 func testAcceptNothingToInt(ac1: @autoclosure () -> Int) {
   // expected-note@-1{{parameter 'ac1' is implicitly non-escaping because it was declared @autoclosure}}
   acceptNothingToInt({ac1($0)})
-  // expected-error@-1{{cannot convert value of type '(_) -> Int' to expected argument type '() -> Int'}}
+  // expected-error@-1{{contextual closure type '() -> Int' expects 0 arguments, but 1 was used in closure body}}
   // FIXME: expected-error@-2{{closure use of non-escaping parameter 'ac1' may allow it to escape}}
 }
 
@@ -323,4 +323,4 @@ func r20789423() {
 
 }
 
-
+let f: (Int, Int) -> Void = { x in }  // expected-error {{contextual closure type specifies '(Int, Int)', but 1 was used in closure body, try adding extra parentheses around the single tuple argument}}

test/expr/closure/closures.swift

@@ -1,6 +1,6 @@
 // RUN: %target-parse-verify-swift
 
-var func6 : (_ fn : (Int,Int) -> Int) -> ()
+var func6 : (_ fn : ((Int, Int)) -> Int) -> ()
 var func6a : ((Int, Int) -> Int) -> ()
 var func6b : (Int, (Int, Int) -> Int) -> ()
 func func6c(_ f: (Int, Int) -> Int, _ n: Int = 0) {} // expected-warning{{prior to parameters}}
@@ -65,7 +65,7 @@ func funcdecl5(_ a: Int, _ y: Int) {
   func6({a,b in 4.0 })  // expected-error {{cannot convert value of type 'Double' to closure result type 'Int'}}
 
   // TODO: This diagnostic can be improved: rdar://22128205
-  func6({(a : Float, b) in 4 }) // expected-error {{cannot convert value of type '(Float, _) -> Int' to expected argument type '(Int, Int) -> Int'}}
+  func6({(a : Float, b) in 4 }) // expected-error {{cannot convert value of type '(Float, _) -> Int' to expected argument type '((Int, Int)) -> Int'}}
 
 
 

test/expr/closure/default_args.swift

@@ -3,8 +3,8 @@
 func simple_default_args() {
   // <rdar://problem/22753605> QoI: bad diagnostic when closure has default argument
   let _ : (Int) -> Int = {(x : Int = 1) in x+1} // expected-error{{default arguments are not allowed in closures}} {{36-39=}}
-  let _ : () -> Int = {(_ x : Int = 1) in x+1} // expected-error{{cannot convert value of type '(Int) -> Int' to specified type '() -> Int'}} expected-error {{default arguments are not allowed in closures}} {{35-38=}}
-  let _ : () -> Int = {(_ x : Int) in x+1} // expected-error{{cannot convert value of type '(Int) -> Int' to specified type '() -> Int'}}
+  let _ : () -> Int = {(_ x : Int = 1) in x+1} // expected-error{{contextual closure type '() -> Int' expects 0 arguments, but 1 was used in closure body}} expected-error {{default arguments are not allowed in closures}} {{35-38=}}
+  let _ : () -> Int = {(_ x : Int) in x+1} // expected-error{{contextual closure type '() -> Int' expects 0 arguments, but 1 was used in closure body}}
 }
 
 func func_default_args() {

test/expr/expressions.swift

@@ -113,7 +113,7 @@ func funcdecl7(_ a: Int, b: (c: Int, d: Int), third: (c: Int, d: Int)) -> Int {
 }
 
 // Error recovery.
-func testfunc2 (_: ((), Int) -> Int) -> Int {}
+func testfunc2 (_: (((), Int)) -> Int) -> Int {}
 func errorRecovery() {
   testfunc2({ $0 + 1 }) // expected-error {{binary operator '+' cannot be applied to operands of type '((), Int)' and 'Int'}} expected-note {{expected an argument list of type '(Int, Int)'}}