Enable parsing of optional strings

llvm/include/llvm/Support/CommandLine.h

@@ -1192,6 +1192,31 @@ class LLVM_ABI parser<std::string> : public basic_parser<std::string> {
 
 //--------------------------------------------------
 
+template <>
+class LLVM_ABI parser<std::optional<std::string>>
+    : public basic_parser<std::optional<std::string>> {
+public:
+  parser(Option &O) : basic_parser(O) {}
+
+  // Return true on error.
+  bool parse(Option &, StringRef, StringRef Arg,
+             std::optional<std::string> &Value) {
+    Value = Arg.str();
+    return false;
+  }
+
+  // Overload in subclass to provide a better default value.
+  StringRef getValueName() const override { return "optional string"; }
+
+  void printOptionDiff(const Option &O, std::optional<StringRef> V,
+                       const OptVal &Default, size_t GlobalWidth) const;
+
+  // An out-of-line virtual method to provide a 'home' for this class.
+  void anchor() override;
+};
+
+//--------------------------------------------------
+
 extern template class LLVM_TEMPLATE_ABI basic_parser<char>;
 
 template <> class LLVM_ABI parser<char> : public basic_parser<char> {

llvm/lib/Support/CommandLine.cpp

@@ -101,6 +101,7 @@ void parser<unsigned long long>::anchor() {}
 void parser<double>::anchor() {}
 void parser<float>::anchor() {}
 void parser<std::string>::anchor() {}
+void parser<std::optional<std::string>>::anchor() {}
 void parser<char>::anchor() {}
 
 // These anchor functions instantiate opt<T> and reference its virtual
@@ -2259,6 +2260,22 @@ void parser<std::string>::printOptionDiff(const Option &O, StringRef V,
   outs() << ")\n";
 }
 
+void parser<std::optional<std::string>>::printOptionDiff(
+    const Option &O, std::optional<StringRef> V,
+    const OptionValue<std::optional<std::string>> &D,
+    size_t GlobalWidth) const {
+  printOptionName(O, GlobalWidth);
+  outs() << "= " << V;
+  size_t VSize = V.has_value() ? V.value().size() : 0;
+  size_t NumSpaces = MaxOptWidth > VSize ? MaxOptWidth - VSize : 0;
+  outs().indent(NumSpaces) << " (default: ";
+  if (D.hasValue() && D.getValue().has_value())
+    outs() << D.getValue();
+  else
+    outs() << "*no value*";
+  outs() << ")\n";
+}
+
 // Print a placeholder for options that don't yet support printOptionDiff().
 void basic_parser_impl::printOptionNoValue(const Option &O,
                                            size_t GlobalWidth) const {

llvm/unittests/Support/CommandLineTest.cpp

@@ -2117,6 +2117,22 @@ TEST(CommandLineTest, ConsumeAfterTwoPositionals) {
   EXPECT_TRUE(Errs.empty());
 }
 
+TEST(CommandLineTest, ConsumeOptionalString) {
+  cl::ResetCommandLineParser();
+
+  StackOption<std::optional<std::string>, cl::opt<std::optional<std::string>>>
+      Input("input");
+
+  const char *Args[] = {"prog", "--input=\"value\""};
+
+  std::string Errs;
+  raw_string_ostream OS(Errs);
+  ASSERT_TRUE(cl::ParseCommandLineOptions(2, Args, StringRef(), &OS));
+  ASSERT_TRUE(Input.has_value());
+  EXPECT_EQ("\"value\"", *Input);
+  EXPECT_TRUE(Errs.empty());
+}
+
 TEST(CommandLineTest, ResetAllOptionOccurrences) {
   cl::ResetCommandLineParser();