Option spell checking: Penalize delimiter flags if input has no argument

[thakis]

Summary

If the user passes a flag like -version to a program, it's more likely
they mean --version than -version:, since there's no parameter
passed. Hence, give delimited arguments a penalty of 1 if the user input
doesn't contain the delimiter or no data after it.

The motivation is that with this, lld-link can suggest "--version"
instead of "-version:" for "-version" and "-nodefaultlib" instead of
"-nodefaultlib:" for "-nodefaultlibs".

[MaskRay]

llvm/lib/Option/OptTable.cpp

311

++Distance;

[thakis]

Thanks! Landing with suggested tweak applied.

llvm/lib/Option/OptTable.cpp

for (const Info &CandidateInfo :
     // "--help" over "-help".
     for (int P = 0;
          const char *const CandidatePrefix = CandidateInfo.Prefixes[P]; P++) {
       std::string Candidate = (CandidatePrefix + CandidateName).str();
       StringRef CandidateRef = Candidate;
       unsigned Distance =
           CandidateRef.edit_distance(NormalizedName, /*AllowReplacements=*/true,
                                      /*MaxEditDistance=*/BestDistance);
+      if (RHS.empty() && CandidateHasDelimiter) {
+        // The Candidate ends with a = or : delimiter, but the option passed in
+        // didn't contain the delimiter (or doesn't have anything after it).
+        // In that case, penalize the correction: `-nodefaultlibs` is more
+        // likely to be a spello for `-nodefaultlib` than `-nodefaultlib:` even
+        // though both have an unmodified editing distance of 1, since the
+        // latter would need an argument.
+        Distance++;
+      }
       if (Distance < BestDistance) {
         BestDistance = Distance;
         NearestString = (Candidate + RHS).str();
       }
     }
   }
   return BestDistance;
 }

llvm/unittests/Option/OptionParsingTest.cpp

TEST(Option, FindNearest) {
   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");
 
-  // `--glormp` should have an editing distance of 1 to `--glormp=`.
-  EXPECT_EQ(1U, T.findNearest("--glormp", Nearest));
-  EXPECT_EQ(Nearest, "--glormp=");
-  EXPECT_EQ(0U, T.findNearest("--glormp=foo", Nearest));
+  // `--glormp` should have an editing distance > 0 from `--glormp=`.
+  EXPECT_GT(T.findNearest("--glorrmp", Nearest), 0U);
+  EXPECT_EQ(Nearest, "--glorrmp=");
+  EXPECT_EQ(0U, T.findNearest("--glorrmp=foo", Nearest));
+
+  // `--blurmps` should correct to `--blurmp`, not `--blurmp=`, even though
+  // both naively have an editing distance of 1.
+  EXPECT_EQ(1U, T.findNearest("--blurmps", Nearest));
+  EXPECT_EQ(Nearest, "--blurmp");
+
+  // ...but `--blurmps=foo` should correct to `--blurmp=foo`.
+  EXPECT_EQ(1U, T.findNearest("--blurmps=foo", Nearest));
+  EXPECT_EQ(Nearest, "--blurmp=foo");
 
   // Flags should be included and excluded as specified.
   EXPECT_EQ(1U, T.findNearest("-doopf", Nearest, /*FlagsToInclude=*/OptFlag2));
   EXPECT_EQ(Nearest, "-doopf2");
   EXPECT_EQ(1U, T.findNearest("-doopf", Nearest,
                               /*FlagsToInclude=*/0,
                               /*FlagsToExclude=*/OptFlag2));
   EXPECT_EQ(Nearest, "-doopf1");

llvm/unittests/Option/Opts.td

 def Blorp : Flag<["-", "--"], "blorp">, HelpText<"The blorp option">, Flags<[OptFlag1]>;
 def Blarn : Flag<["--", "-"], "blarn">, HelpText<"The blarn 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 Glormp_eq : Flag<["--"], "glormp=">;
+def Glorrmp_eq : Flag<["--"], "glorrmp=">;
+
+def Blurmpq : Flag<["--"], "blurmp">;
+def Blurmpq_eq : Flag<["--"], "blurmp=">;
 
 def DashDash : Option<["--"], "", KIND_REMAINING_ARGS>;