[clang] [clang-tools-extra] [clang] Don't add documentation comments to the AST if not requested (PR #206363)

[Aaron Ballman via cfe-commits]

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@@ -2703,11 +2705,37 @@ LambdaScopeInfo *Sema::getCurGenericLambda() {
   return nullptr;
 }
 
+bool Sema::shouldRetainCommentsFromLexer(SourceLocation Loc) const {
+  if (LangOpts.CommentOpts.ParseAllComments)
+    return true;
+
+  if (LangOpts.CommentOpts.RetainComments)
+    return true;
+
+  // When building a PCH the comments are serialized into the AST file
+  // so downstream consumers like clangd) can retrieve documentation, and the
+  // incremental/REPL front end may query them interactively.
+  if (TUKind != TU_Complete)
+    return true;
+
+  if (PP.isCodeCompletionEnabled())
+    return true;
+
+  // Keep the comment if -Wdocumentation is enabled at its location (checking
+  // the location handles warnings turned on by `#pragma clang diagnostic`).
+  if (!Diags.isIgnored(diag::warn_doc_param_not_found, Loc) ||
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AaronBallman wrote:

We don't have anything like `Diags.areAnyIgnored("-Wdocumentation")` which is the interface I naively think would make sense for this sort of thing.

Actually, I think the current approach here isn't viable. The user could disable one of the diagnostics we're checking for via `#pragma clang diagnostic` but still enable all of the other diagnostics in the same group. So I think we might need to add an interface like `areAnyIgnored` to do this correctly and efficiently...

https://github.com/llvm/llvm-project/pull/206363