[Diagnostics] Store synthesized arguments in missing arguments diagnostic

Since we are about to start diagnosing more than just closures,
we need information about what synthesized arguments look like.

Author: xedin

lib/Sema/CSDiagnostics.cpp

@@ -3598,14 +3598,15 @@ bool MissingArgumentsFailure::diagnoseClosure(ClosureExpr *closure) {
   if (!funcType)
     return false;
 
-  auto diff = funcType->getNumParams() - NumSynthesized;
+  unsigned numSynthesized = SynthesizedArgs.size();
+  auto diff = funcType->getNumParams() - numSynthesized;
 
   // If the closure didn't specify any arguments and it is in a context that
   // needs some, produce a fixit to turn "{...}" into "{ _,_ in ...}".
   if (diff == 0) {
     auto diag =
         emitDiagnostic(closure->getStartLoc(),
-                       diag::closure_argument_list_missing, NumSynthesized);
+                       diag::closure_argument_list_missing, numSynthesized);
 
     std::string fixText; // Let's provide fixits for up to 10 args.
     if (funcType->getNumParams() <= 10) {
@@ -3649,9 +3650,9 @@ bool MissingArgumentsFailure::diagnoseClosure(ClosureExpr *closure) {
     llvm::raw_svector_ostream OS(fixIt);
 
     OS << ",";
-    for (unsigned i = 0; i != NumSynthesized; ++i) {
+    for (unsigned i = 0; i != numSynthesized; ++i) {
       OS << ((onlyAnonymousParams) ? "_" : "<#arg#>");
-      OS << ((i == NumSynthesized - 1) ? " " : ",");
+      OS << ((i == numSynthesized - 1) ? " " : ",");
     }
 
     diag.fixItInsertAfter(params->getEndLoc(), OS.str());

lib/Sema/CSDiagnostics.h

@@ -1186,12 +1186,14 @@ class ImplicitInitOnNonConstMetatypeFailure final
 class MissingArgumentsFailure final : public FailureDiagnostic {
   using Param = AnyFunctionType::Param;
 
-  unsigned NumSynthesized;
+  SmallVector<Param, 4> SynthesizedArgs;
 
 public:
   MissingArgumentsFailure(Expr *root, ConstraintSystem &cs,
-                          unsigned numSynthesized, ConstraintLocator *locator)
-      : FailureDiagnostic(root, cs, locator), NumSynthesized(numSynthesized) {}
+                          ArrayRef<Param> synthesizedArgs,
+                          ConstraintLocator *locator)
+      : FailureDiagnostic(root, cs, locator),
+        SynthesizedArgs(synthesizedArgs.begin(), synthesizedArgs.end()) {}
 
   bool diagnoseAsError() override;
 

lib/Sema/CSFix.cpp

@@ -478,7 +478,8 @@ AllowClosureParamDestructuring::create(ConstraintSystem &cs,
 
 bool AddMissingArguments::diagnose(Expr *root, bool asNote) const {
   auto &cs = getConstraintSystem();
-  MissingArgumentsFailure failure(root, cs, NumSynthesized, getLocator());
+  MissingArgumentsFailure failure(root, cs, getSynthesizedArguments(),
+                                  getLocator());
   return failure.diagnose(asNote);
 }