[clangd] Actually parse Index section of the YAML file.

This fixes a bug in dbf486c, which
introduced the Index section of the config, but did not register the
parse method, so it didn't work in a YAML file (but did in a test).

Differential Revision: https://reviews.llvm.org/D87710

Author: gislan

clang-tools-extra/clangd/ConfigYAML.cpp

@@ -38,6 +38,7 @@ class Parser {
     DictParser Dict("Config", this);
     Dict.handle("If", [&](Node &N) { parse(F.If, N); });
     Dict.handle("CompileFlags", [&](Node &N) { parse(F.CompileFlags, N); });
+    Dict.handle("Index", [&](Node &N) { parse(F.Index, N); });
     Dict.parse(N);
     return !(N.failed() || HadError);
   }

clang-tools-extra/clangd/unittests/ConfigYAMLTests.cpp

@@ -47,16 +47,21 @@ CompileFlags: { Add: [foo, bar] }
   Add: |
     b
     az
+---
+Index:
+  Background: Skip
   )yaml";
   auto Results = Fragment::parseYAML(YAML, "config.yaml", Diags.callback());
   EXPECT_THAT(Diags.Diagnostics, IsEmpty());
-  ASSERT_EQ(Results.size(), 2u);
-  EXPECT_FALSE(Results.front().If.HasUnrecognizedCondition);
-  EXPECT_THAT(Results.front().If.PathMatch, ElementsAre(Val("abc")));
-  EXPECT_THAT(Results.front().CompileFlags.Add,
-              ElementsAre(Val("foo"), Val("bar")));
+  ASSERT_EQ(Results.size(), 3u);
+  EXPECT_FALSE(Results[0].If.HasUnrecognizedCondition);
+  EXPECT_THAT(Results[0].If.PathMatch, ElementsAre(Val("abc")));
+  EXPECT_THAT(Results[0].CompileFlags.Add, ElementsAre(Val("foo"), Val("bar")));
+
+  EXPECT_THAT(Results[1].CompileFlags.Add, ElementsAre(Val("b\naz\n")));
 
-  EXPECT_THAT(Results.back().CompileFlags.Add, ElementsAre(Val("b\naz\n")));
+  ASSERT_TRUE(Results[2].Index.Background);
+  EXPECT_EQ("Skip", *Results[2].Index.Background.getValue());
 }
 
 TEST(ParseYAML, Locations) {