[clangd] Add flag to control #import include insertions

[dgoldman]

Summary

This will be disabled by default, hopefully we can enable for the next
major release.

[kadircet]

clang-tools-extra/clangd/tool/ClangdMain.cpp

271

... accepting code completions or fixing includes in Objective-C code.

272

s/false/CodeCompleteOptions().ImportInsertions/

[dgoldman]

Update comment + default value

clang-tools-extra/clangd/CodeComplete.h

struct CodeCompleteOptions {
   /// Whether to present doc comments as plain-text or markdown.
   MarkupKind DocumentationFormat = MarkupKind::PlainText;
 
   enum IncludeInsertion {
     IWYU,
     NeverInsert,
   } InsertIncludes = IncludeInsertion::IWYU;
 
+  /// Whether include insertions for Objective-C code should use #import instead
+  /// of #include.
+  bool ImportInsertions = false;
+
   /// A visual indicator to prepend to the completion label to indicate whether
   /// completion result would trigger an #include insertion or not.
   struct IncludeInsertionIndicator {
     std::string Insert = "•";
     std::string NoInsert = " ";
   } IncludeIndicator;
 
   /// Expose origins of completion items in the label (for debugging).

clang-tools-extra/clangd/tool/ClangdMain.cpp

values(
                    "Insert the owning header for top-level symbols, unless the "
                    "header is already directly included or the symbol is "
                    "forward-declared"),
         clEnumValN(
             CodeCompleteOptions::NeverInsert, "never",
             "Never insert #include directives as part of code completion")),
 };
 
+opt<bool> ImportInsertions{
+    "import-insertions",
+    cat(Features),
+    desc("If header insertion is enabled, add #import directives when "
+         "accepting code completions or fixing includes in Objective-C code"),
+    init(CodeCompleteOptions().ImportInsertions),
+};
+
 opt<bool> IncludeCleanerStdlib{
     "include-cleaner-stdlib",
     cat(Features),
     desc("Apply include-cleaner analysis to standard library headers "
          "(immature!)"),
     init(false),
     Hidden,
 };
#endif
   Opts.MemoryCleanup = getMemoryCleanupFunction();
 
   Opts.CodeComplete.IncludeIneligibleResults = IncludeIneligibleResults;
   Opts.CodeComplete.Limit = LimitResults;
   if (CompletionStyle.getNumOccurrences())
     Opts.CodeComplete.BundleOverloads = CompletionStyle != Detailed;
   Opts.CodeComplete.ShowOrigins = ShowOrigins;
   Opts.CodeComplete.InsertIncludes = HeaderInsertion;
+  Opts.CodeComplete.ImportInsertions = ImportInsertions;
   if (!HeaderInsertionDecorators) {
     Opts.CodeComplete.IncludeIndicator.Insert.clear();
     Opts.CodeComplete.IncludeIndicator.NoInsert.clear();
   }
   Opts.CodeComplete.EnableFunctionArgSnippets = EnableFunctionArgSnippets;
   Opts.CodeComplete.RunParser = CodeCompletionParse;
   Opts.CodeComplete.RankingModel = RankingModel;