Gracefully handle incorrect SwiftName arg count

lib/ClangImporter/ImportDecl.cpp

@@ -6674,6 +6674,7 @@ Decl *SwiftDeclConverter::importGlobalAsInitializer(
   ArrayRef<Identifier> argNames = name.getArgumentNames();
 
   ParameterList *parameterList = nullptr;
+  DeclName nameBeforeAdjustment;
   if (argNames.size() == 1 && decl->getNumParams() == 0) {
     // Special case: We need to create an empty first parameter for our
     // argument label
@@ -6690,6 +6691,25 @@ Decl *SwiftDeclConverter::importGlobalAsInitializer(
         dc, decl, {decl->param_begin(), decl->param_end()}, decl->isVariadic(),
         allowNSUIntegerAsInt, argNames, /*genericParams=*/{},
         /*resultType=*/nullptr, /*hasBoundsAnnotatedParam=*/nullptr);
+
+    if (name && parameterList && argNames.size() != parameterList->size()) {
+      // Remember that the name has changed.
+      nameBeforeAdjustment = name;
+
+      // Add or remove argument labels as needed to match `parameterList`.
+      SmallVector<Identifier, 16> newArgNames;
+      llvm::append_range(newArgNames, argNames);
+      while (newArgNames.size() > parameterList->size())
+        newArgNames.pop_back();
+      while (newArgNames.size() < parameterList->size()) {
+        auto param = parameterList->get(newArgNames.size());
+        newArgNames.push_back(param->getArgumentName());
+      }
+
+      // Construct the new name.
+      name = DeclName(Impl.SwiftContext, name.getBaseName(), newArgNames);
+      argNames = name.getArgumentNames();
+    }
   }
   if (!parameterList)
     return nullptr;
@@ -6727,6 +6747,21 @@ Decl *SwiftDeclConverter::importGlobalAsInitializer(
   result->setIsObjC(false);
   result->setIsDynamic(false);
 
+  if (nameBeforeAdjustment) {
+    SmallString<16> message;
+    llvm::raw_svector_ostream os(message);
+    os << "declared Swift name '" << nameBeforeAdjustment
+       << "' was adjusted to '" << name
+       << "' because it does not have the correct number of parameters ("
+       << nameBeforeAdjustment.getArgumentNames().size() << " vs. "
+       << name.getArgumentNames().size()
+       << "); please report this to its maintainer";
+
+    auto attr = AvailableAttr::createUniversallyDeprecated(Impl.SwiftContext,
+                    Impl.SwiftContext.AllocateCopy(message.str()), "");
+    result->getAttrs().add(attr);
+  }
+
   finishFuncDecl(decl, result);
   if (correctSwiftName)
     markAsVariant(result, *correctSwiftName);

test/ClangImporter/Inputs/custom-modules/SwiftName.h

@@ -32,6 +32,8 @@ typedef int my_int_t SWIFT_NAME(MyInt);
 void spuriousAPINotedSwiftName(int);
 void poorlyNamedFunction(const char *);
 
+PointType readPoint(const char *path, void **errorOut) SWIFT_NAME(Point.init(path:));
+
 struct BoxForConstants {
   int dummy;
 };

test/ClangImporter/attr-swift_name_renaming.swift

@@ -22,6 +22,9 @@ func test() {
   var p = Point()
   var p2 = PointType() // FIXME: should provide Fix-It expected-error{{cannot find 'PointType' in scope}} {{none}}
 
+  // Initializers with incorrect argument count (rdar://141124373)
+  var p3 = Point(path: "/dev/zero", nil) // expected-warning {{'init(path:_:)' is deprecated: declared Swift name 'init(path:)' was adjusted to 'init(path:_:)' because it does not have the correct number of parameters (1 vs. 2); please report this to its maintainer}}
+
   // Field name remapping
   p.x = 7