[Support] Indent multi-line descr of enum cli options.

As noted in https://reviews.llvm.org/D93459, the formatting of
multi-line descriptions of clEnumValN and the likes is unfavorable.
Thus this patch adds support for correctly indenting these.

Reviewed By: serge-sans-paille

Differential Revision: https://reviews.llvm.org/D93494

include/llvm/Support/CommandLine.h

@@ -369,9 +369,22 @@ public:
 
   virtual void setDefault() = 0;
 
+  // Prints the help string for an option.
+  //
+  // This maintains the Indent for multi-line descriptions.
+  // FirstLineIndentedBy is the count of chars of the first line
+  //      i.e. the one containing the --<option name>.
   static void printHelpStr(StringRef HelpStr, size_t Indent,
                            size_t FirstLineIndentedBy);
 
+  // Prints the help string for an enum value.
+  //
+  // This maintains the Indent for multi-line descriptions.
+  // FirstLineIndentedBy is the count of chars of the first line
+  //      i.e. the one containing the =<value>.
+  static void printEnumValHelpStr(StringRef HelpStr, size_t Indent,
+                                  size_t FirstLineIndentedBy);
+
   virtual void getExtraOptionNames(SmallVectorImpl<StringRef> &) {}
 
   // addOccurrence - Wrapper around handleOccurrence that enforces Flags.

lib/Support/CommandLine.cpp

@@ -1726,6 +1726,19 @@ void Option::printHelpStr(StringRef HelpStr, size_t Indent,
   }
 }
 
+void Option::printEnumValHelpStr(StringRef HelpStr, size_t BaseIndent,
+                                 size_t FirstLineIndentedBy) {
+  const StringRef ValHelpPrefix = "  ";
+  assert(BaseIndent >= FirstLineIndentedBy + ValHelpPrefix.size());
+  std::pair<StringRef, StringRef> Split = HelpStr.split('\n');
+  outs().indent(BaseIndent - FirstLineIndentedBy)
+      << ArgHelpPrefix << ValHelpPrefix << Split.first << "\n";
+  while (!Split.second.empty()) {
+    Split = Split.second.split('\n');
+    outs().indent(BaseIndent + ValHelpPrefix.size()) << Split.first << "\n";
+  }
+}
+
 // Print out the option for the alias.
 void alias::printOptionInfo(size_t GlobalWidth) const {
   outs() << PrintArg(ArgStr);
@@ -1971,17 +1984,17 @@ void generic_parser_base::printOptionInfo(const Option &O,
       StringRef Description = getDescription(i);
       if (!shouldPrintOption(OptionName, Description, O))
         continue;
-      assert(GlobalWidth >= OptionName.size() + OptionPrefixesSize);
+      size_t FirstLineIndent = OptionName.size() + OptionPrefixesSize;
-      size_t NumSpaces = GlobalWidth - OptionName.size() - OptionPrefixesSize;
       outs() << OptionPrefix << OptionName;
       if (OptionName.empty()) {
         outs() << EmptyOption;
-        assert(NumSpaces >= EmptyOption.size());
+        assert(FirstLineIndent >= EmptyOption.size());
-        NumSpaces -= EmptyOption.size();
+        FirstLineIndent += EmptyOption.size();
       }
       if (!Description.empty())
-        outs().indent(NumSpaces) << ArgHelpPrefix << "  " << Description;
+        Option::printEnumValHelpStr(Description, GlobalWidth, FirstLineIndent);
-      outs() << '\n';
+      else
+        outs() << '\n';
     }
   } else {
     if (!O.HelpStr.empty())

unittests/Support/CommandLineTest.cpp

@@ -1263,6 +1263,28 @@ TEST_F(PrintOptionInfoTest, PrintOptionInfoEmptyValueDescription) {
   // clang-format on
 }
 
+TEST_F(PrintOptionInfoTest, PrintOptionInfoMultilineValueDescription) {
+  std::string Output =
+      runTest(cl::ValueRequired,
+              cl::values(clEnumValN(OptionValue::Val, "v1",
+                                    "This is the first enum value\n"
+                                    "which has a really long description\n"
+                                    "thus it is multi-line."),
+                         clEnumValN(OptionValue::Val, "",
+                                    "This is an unnamed enum value option\n"
+                                    "Should be indented as well")));
+
+  // clang-format off
+  EXPECT_EQ(Output,
+            ("  --" + Opt + "=<value> - " + HelpText + "\n"
+             "    =v1                 -   This is the first enum value\n"
+             "                            which has a really long description\n"
+             "                            thus it is multi-line.\n"
+             "    =<empty>            -   This is an unnamed enum value option\n"
+             "                            Should be indented as well\n").str());
+  // clang-format on
+}
+
 class GetOptionWidthTest : public ::testing::Test {
 public:
   enum class OptionValue { Val };