[Option] Fix PR37006 prefix choice in findNearest

Summary:
In https://bugs.llvm.org/show_bug.cgi?id=37006 Nico Weber points out a
flaw in `OptTable::findNearest`: if an option "foo"'s prefixes are "--"
and "-", then the nearest option for "--fob" will be "-foo". This is
incorrect, however, since the function is expected to return "--foo".

The bug is due to a naive loop that attempts to predetermines which
prefix is best. Instead, compute the edit distance for each prefix/name
pair.

Test Plan: `check-llvm`

Reviewers: thakis

Reviewed By: thakis

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D46776

llvm-svn: 332299

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/unittests/Option/OptionParsingTest.cpp b/llvm/unittests/Option/OptionParsingTest.cpp
index eef21ab5120..99c1ef32476 100644
--- a/llvm/unittests/Option/OptionParsingTest.cpp
+++ b/llvm/unittests/Option/OptionParsingTest.cpp
@@ -283,6 +283,10 @@ TEST(Option, FindNearest) {
   EXPECT_EQ(Nearest, "-blorp");
   EXPECT_EQ(1U, T.findNearest("--blorm", Nearest));
   EXPECT_EQ(Nearest, "--blorp");
+  EXPECT_EQ(1U, T.findNearest("-blarg", Nearest));
+  EXPECT_EQ(Nearest, "-blarn");
+  EXPECT_EQ(1U, T.findNearest("--blarm", Nearest));
+  EXPECT_EQ(Nearest, "--blarn");
   EXPECT_EQ(1U, T.findNearest("-fjormp", Nearest));
   EXPECT_EQ(Nearest, "--fjormp");