[ObjC] Improve naming of arguments to Objective-C methods

Detect and remove common prefixes used on selectors so that their
argument names are more natural. For instance, a selector of
`initWithURL:withStagedURL`: now ends up with arguments named `URL` and
`stagedURL`, rather than `initWithURL` and `withStagedURL`.

Author: bdash

objectivec/objc.cpp

@@ -3,6 +3,41 @@
 
 using namespace BinaryNinja;
 
+namespace {
+
+// Given a selector component such as `initWithPath' and a prefix of `initWith`, returns `path`.
+std::optional<std::string> SelectorComponentWithoutPrefix(std::string_view prefix, std::string_view component)
+{
+	if (component.size() <= prefix.size() || component.rfind(prefix.data(), 0) != 0
+		|| !isupper(component[prefix.size()]))
+	{
+		return std::nullopt;
+	}
+
+	std::string result(component.substr(prefix.size()));
+
+	// Lowercase the first character if the second character is not also uppercase.
+	// This ensures we leave initialisms such as `URL` alone.
+	if (result.size() > 1 && islower(result[1]))
+		result[0] = tolower(result[0]);
+
+	return result;
+}
+
+std::string ArgumentNameFromSelectorComponent(std::string component)
+{
+	// TODO: Handle other common patterns such as <do some action>With<arg>: and <do some action>For<arg>:
+	for (const auto& prefix : {"initWith", "with", "and", "using", "set", "read", "to", "for"})
+	{
+		if (auto argumentName = SelectorComponentWithoutPrefix(prefix, component); argumentName.has_value())
+			return std::move(*argumentName);
+	}
+
+	return component;
+}
+
+}  // namespace
+
 Ref<Metadata> ObjCProcessor::SerializeMethod(uint64_t loc, const Method& method)
 {
 	std::map<std::string, Ref<Metadata>> methodMeta;
@@ -1099,10 +1134,13 @@ bool ObjCProcessor::ApplyMethodType(Class& cls, Method& method, bool isInstanceM
 
 	for (size_t i = 3; i < typeTokens.size(); i++)
 	{
-		std::string suffix;
+		std::string name;
+		if (selectorTokens.size() > i - 3)
+			name = ArgumentNameFromSelectorComponent(selectorTokens[i - 3]);
+		else
+			name = "arg";
 
-		params.push_back({selectorTokens.size() > i - 3 ? selectorTokens[i - 3] : "arg",
-			typeForQualifiedNameOrType(typeTokens[i]), true, BinaryNinja::Variable()});
+		params.push_back({std::move(name), typeForQualifiedNameOrType(typeTokens[i]), true, BinaryNinja::Variable()});
 	}
 
 	auto funcType = BinaryNinja::Type::FunctionType(retType, cc, params);