[Option] For typo '-foo', suggest '--foo'

[modocache]

Summary

https://reviews.llvm.org/rL321877 introduced the OptTable::findNearest
method, to find the closest edit distance option for a given string.
However, the implementation contained a bug: for a typo -foo with an
edit distance of 1 away from a valid option --foo, findNearest
would suggest a nearby option of foo. That is, the result would not
include the -- prefix, and so was not a valid option.

Fix the bug by ensuring that the prefix string is initialized to one of
the valid prefixes for the option.

Test Plan: check-llvm-unit

[jroelofs]

LGTM

[modocache]

Great, thanks for the quick review, @jroelofs!

[thakis]

lib/Option/OptTable.cpp

281

This relies on '--' being later in Prefixes than '-'. If '--' is Prefixes[0] is -- and then Prefixes[1] is -, then Option.startswith (Prefixes[1]) is true and we switch from -- to - for flags that start with --.

And -- being later in Prefixes isn't guaranteed.

[thakis]

lib/Option/OptTable.cpp

281

(A fix for this is at https://reviews.llvm.org/D46776)

lib/Option/OptTable.cpp

if (CandidateInfo.Flags & FlagsToExclude)
       continue;
 
     // Ignore positional argument option candidates (which do not
     // have prefixes).
     if (!CandidateInfo.Prefixes)
       continue;
     // Find the most appropriate prefix. For example, if a user asks for
     // "--helm", suggest "--help" over "-help".
-    StringRef Prefix;
-    for (int P = 0; CandidateInfo.Prefixes[P]; P++) {
+    StringRef Prefix = CandidateInfo.Prefixes[0];
+    for (int P = 1; CandidateInfo.Prefixes[P]; P++) {
       if (Option.startswith(CandidateInfo.Prefixes[P]))
         Prefix = CandidateInfo.Prefixes[P];
     }
 
     // Check if the candidate ends with a character commonly used when
     // delimiting an option from its value, such as '=' or ':'. If it does,
     // attempt to split the given option based on that delimiter.
     std::string Delimiter = "";

unittests/Option/OptionParsingTest.cpp

TEST(Option, FindNearest) {
   EXPECT_GT(T.findNearest("--C=foo", Nearest), 4U);
 
   // The nearest candidate should mirror the amount of prefix
   // characters used in the original string.
   EXPECT_EQ(1U, T.findNearest("-blorb", Nearest));
   EXPECT_EQ(Nearest, "-blorp");
   EXPECT_EQ(1U, T.findNearest("--blorm", Nearest));
   EXPECT_EQ(Nearest, "--blorp");
+  EXPECT_EQ(1U, T.findNearest("-fjormp", Nearest));
+  EXPECT_EQ(Nearest, "--fjormp");
 
   // The nearest candidate respects the prefix and value delimiter
   // of the original string.
   EXPECT_EQ(1U, T.findNearest("/framb:foo", Nearest));
   EXPECT_EQ(Nearest, "/cramb:foo");
 
   // Flags should be included and excluded as specified.
   EXPECT_EQ(1U, T.findNearest("-doopf", Nearest, /*FlagsToInclude=*/OptFlag2));

unittests/Option/Opts.td

 
 def SlurpJoined : Option<["-"], "slurpjoined", KIND_REMAINING_ARGS_JOINED>;
 
 def Blorp : Flag<["-", "--"], "blorp">, HelpText<"The blorp option">, Flags<[OptFlag1]>;
 def Cramb : Joined<["/"], "cramb:">, HelpText<"The cramb option">, MetaVarName<"CRAMB">, Flags<[OptFlag1]>;
 def Doopf1 : Flag<["-"], "doopf1">, HelpText<"The doopf1 option">, Flags<[OptFlag1]>;
 def Doopf2 : Flag<["-"], "doopf2">, HelpText<"The doopf2 option">, Flags<[OptFlag2]>;
 def Ermgh : Joined<["--"], "ermgh">, HelpText<"The ermgh option">, MetaVarName<"ERMGH">, Flags<[OptFlag1]>;
+def Fjormp : Flag<["--"], "fjormp">, HelpText<"The fjormp option">, Flags<[OptFlag1]>;
 def DashDash : Option<["--"], "", KIND_REMAINING_ARGS>;