[ConstraintSystem] NFC: Remove workarounds related to (now deprecated) CSDiag

lib/Sema/CSApply.cpp

@@ -2285,16 +2285,8 @@ namespace {
       auto locator = cs.getConstraintLocator(expr);
 
       // Find the overload choice used for this declaration reference.
-      auto selected = solution.getOverloadChoiceIfAvailable(locator);
-      if (!selected.hasValue()) {
-        auto *varDecl = cast<VarDecl>(expr->getDecl());
-        assert(varDecl->getType()->is<UnresolvedType>() &&
-               "should only happen for closure arguments in CSDiags");
-        cs.setType(expr, varDecl->getType());
-        return expr;
-      }
-
-      return buildDeclRef(*selected, expr->getNameLoc(), locator,
+      auto selected = solution.getOverloadChoice(locator);
+      return buildDeclRef(selected, expr->getNameLoc(), locator,
                           expr->isImplicit(), expr->getAccessSemantics());
     }
 
@@ -3868,19 +3860,7 @@ namespace {
     Expr *visitEditorPlaceholderExpr(EditorPlaceholderExpr *E) {
       simplifyExprType(E);
       auto valueType = cs.getType(E);
-
-      // TODO(diagnostics): Once all of the diagnostics are moved to
-      // new diagnostics framework this check could be eliminated.
-      //
-      // Only way for this to happen is CSDiag try to re-typecheck
-      // sub-expression which contains this placeholder with
-      // `AllowUnresolvedTypeVariables` flag set.
-      //
-      // A better solution could be to replace placeholders with this
-      // implicit call early on and type-check that call together with
-      // the rest of the constraint system.
-      if (valueType->hasUnresolvedType())
-        return nullptr;
+      assert(!valueType->hasUnresolvedType());
 
       auto &ctx = cs.getASTContext();
       // Synthesize a call to _undefined() of appropriate type.

lib/Sema/CSDiagnostics.cpp

@@ -575,8 +575,6 @@ Optional<Diag<Type, Type>> GenericArgumentsMismatchFailure::getDiagnosticFor(
     return diag::cannot_convert_closure_result;
   case CTP_ArrayElement:
     return diag::cannot_convert_array_element;
-  // TODO(diagnostics): Make dictionary related diagnostics take prescedence
-  // over CSDiag. Currently these won't ever be produced.
   case CTP_DictionaryKey:
     return diag::cannot_convert_dict_key;
   case CTP_DictionaryValue:
@@ -5051,9 +5049,7 @@ void MissingGenericArgumentsFailure::emitGenericSignatureNote(
       continue;
 
     auto type = resolveType(typeVar);
-    // This could happen if the diagnostic is used by CSDiag.
-    if (type->is<TypeVariableType>())
-      continue;
+    assert(!type->is<TypeVariableType>());
 
     // If this is one of the defaulted parameter types, attempt
     // to emit placeholder for it instead of `Any`.

lib/Sema/CSDiagnostics.h

@@ -1689,17 +1689,13 @@ public:
 /// func bar(_ v: Int) { foo(v) } // `Int` is not convertible to `String`
 /// ```
 class ArgumentMismatchFailure : public ContextualFailure {
-  // FIXME: Currently ArgumentMismatchFailure can be used from CSDiag, in which
-  // case it's possible we're not able to resolve the arg apply info. Once
-  // the CSDiag logic has been removed, we should be able to store Info
-  // unwrapped.
-  Optional<FunctionArgApplyInfo> Info;
+  FunctionArgApplyInfo Info;
 
 public:
-  ArgumentMismatchFailure(ConstraintSystem &cs, Type argType,
-                          Type paramType, ConstraintLocator *locator)
+  ArgumentMismatchFailure(ConstraintSystem &cs, Type argType, Type paramType,
+                          ConstraintLocator *locator)
       : ContextualFailure(cs, argType, paramType, locator),
-        Info(cs.getFunctionArgApplyInfo(getLocator())) {}
+        Info(*cs.getFunctionArgApplyInfo(getLocator())) {}
 
   bool diagnoseAsError() override;
   bool diagnoseAsNote() override;
@@ -1722,10 +1718,10 @@ public:
 
 protected:
   /// \returns The position of the argument being diagnosed, starting at 1.
-  unsigned getArgPosition() const { return Info->getArgPosition(); }
+  unsigned getArgPosition() const { return Info.getArgPosition(); }
 
   /// \returns The position of the parameter being diagnosed, starting at 1.
-  unsigned getParamPosition() const { return Info->getParamPosition(); }
+  unsigned getParamPosition() const { return Info.getParamPosition(); }
 
   /// Returns the argument expression being diagnosed.
   ///
@@ -1735,7 +1731,7 @@ protected:
   /// the conversion from T to U may fail. In this case, \c getArgExpr() will
   /// return the (T, U) expression, whereas \c getAnchor() will return the T
   /// expression.
-  Expr *getArgExpr() const { return Info->getArgExpr(); }
+  Expr *getArgExpr() const { return Info.getArgExpr(); }
 
   /// Returns the argument type for the conversion being diagnosed.
   ///
@@ -1748,27 +1744,25 @@ protected:
   /// In this case, \c getArgType() will return T?, whereas \c getFromType()
   /// will return T.
   Type getArgType(bool withSpecifier = false) const {
-    return Info->getArgType(withSpecifier);
+    return Info.getArgType(withSpecifier);
   }
 
   /// \returns A textual description of the argument suitable for diagnostics.
   /// For an argument with an unambiguous label, this will the label. Otherwise
   /// it will be its position in the argument list.
   StringRef getArgDescription(SmallVectorImpl<char> &scratch) const {
-    return Info->getArgDescription(scratch);
+    return Info.getArgDescription(scratch);
   }
 
   /// \returns The interface type for the function being applied.
-  Type getFnInterfaceType() const { return Info->getFnInterfaceType(); }
+  Type getFnInterfaceType() const { return Info.getFnInterfaceType(); }
 
   /// \returns The function type being applied, including any generic
   /// substitutions.
-  FunctionType *getFnType() const { return Info->getFnType(); }
+  FunctionType *getFnType() const { return Info.getFnType(); }
 
   /// \returns The callee for the argument conversion, if any.
-  const ValueDecl *getCallee() const {
-    return Info ? Info->getCallee() : nullptr;
-  }
+  const ValueDecl *getCallee() const { return Info.getCallee(); }
 
   /// \returns The full name of the callee, or a null decl name if there is no
   /// callee.
@@ -1784,7 +1778,7 @@ protected:
   ///
   /// Note this may differ from \c getToType(), see the note on \c getArgType().
   Type getParamType(bool lookThroughAutoclosure = true) const {
-    return Info->getParamType(lookThroughAutoclosure);
+    return Info.getParamType(lookThroughAutoclosure);
   }
 
   /// Returns the type of the parameter involved in the mismatch.
@@ -1794,17 +1788,17 @@ protected:
   ///
   /// Note this may differ from \c getToType(), see the note on \c getArgType().
   Type getParamInterfaceType(bool lookThroughAutoclosure = true) const {
-    return Info->getParamInterfaceType(lookThroughAutoclosure);
+    return Info.getParamInterfaceType(lookThroughAutoclosure);
   }
 
   /// \returns The flags of the parameter involved in the mismatch.
   ParameterTypeFlags getParameterFlags() const {
-    return Info->getParameterFlags();
+    return Info.getParameterFlags();
   }
 
   /// \returns The flags of a parameter at a given index.
   ParameterTypeFlags getParameterFlagsAtIndex(unsigned idx) const {
-    return Info->getParameterFlagsAtIndex(idx);
+    return Info.getParameterFlagsAtIndex(idx);
   }
 
   /// Situations like this:

lib/Sema/CSGen.cpp

@@ -1351,17 +1351,7 @@ namespace {
           knownType = VD->getInterfaceType();
 
         if (knownType) {
-          // If this is a ParamDecl for a closure argument that is a hole,
-          // then this is a situation where CSDiags is trying to perform
-          // error recovery within a ClosureExpr.  Just create a new type
-          // variable for the decl that isn't bound to anything.
-          // This will ensure that it is considered ambiguous.
-          if (knownType && knownType->isHole()) {
-            return CS.createTypeVariable(locator,
-                                         TVO_CanBindToLValue |
-                                         TVO_CanBindToNoEscape);
-          }
-
+          assert(!knownType->isHole());
           // If the known type has an error, bail out.
           if (knownType->hasError()) {
             if (!CS.hasType(E))

lib/Sema/ConstraintSystem.cpp

@@ -453,6 +453,10 @@ ConstraintLocator *ConstraintSystem::getCalleeLocator(
     }
   }
 
+  if (locator->findLast<LocatorPathElt::DynamicCallable>()) {
+    return getConstraintLocator(anchor, LocatorPathElt::ApplyFunction());
+  }
+
   // If we have a locator that starts with a key path component element, we
   // may have a callee given by a property or subscript component.
   if (auto componentElt =
@@ -491,13 +495,10 @@ ConstraintLocator *ConstraintSystem::getCalleeLocator(
     return getConstraintLocator(anchor, ConstraintLocator::SubscriptMember);
 
   auto getSpecialFnCalleeLoc = [&](Type fnTy) -> ConstraintLocator * {
-    // FIXME: We should probably assert that we don't get a type variable
-    // here to make sure we only retrieve callee locators for resolved calls,
-    // ensuring that callee locators don't change after binding a type.
-    // Unfortunately CSDiag currently calls into getCalleeLocator, so all bets
-    // are off. Once we remove that legacy diagnostic logic, we should be able
-    // to assert here.
     fnTy = simplifyType(fnTy);
+    // It's okay for function type to contain type variable(s) e.g.
+    // opened generic function types, but not to be one.
+    assert(!fnTy->is<TypeVariableType>());
 
     // For an apply of a metatype, we have a short-form constructor. Unlike
     // other locators to callees, these are anchored on the apply expression