[PATCH] D118034: [C++20] [Modules] Don't complain about duplicated default template argument across modules

[Chuanqi Xu via Phabricator via cfe-commits]

ChuanqiXu marked 10 inline comments as done.
ChuanqiXu added inline comments.


================
Comment at: clang/lib/Sema/SemaTemplate.cpp:2762
         SawDefaultArgument = true;
-        RedundantDefaultArg = true;
+        if (!OldTypeParm->getImportedOwningModule())
+          RedundantDefaultArg = true;
----------------
rsmith wrote:
> This is the wrong thing to check -- whether the owning module is imported (from an AST file) is irrelevant. We might parse multiple translation units in the same compilation, and we might split a single translation unit into multiple compilations (eg with a precompiled preamble) resulting in some of the same translation unit being in an AST file. What matters is whether the declaration is in the current translation unit or a different translation unit.
> 
> I'm not sure what the best way to detect that is currently. You might be able to just compare `getOwningModule()` of the two declarations, but I don't think that will properly handle cases in the global module fragment, or cases where one template is in the primary module interface unit and another is in a module implementation unit of the same module.
> 
> Ideally I would like for us to create one `TranslationUnitDecl` per translation unit, rather than shoving all imported code into the translation unit of the importer, but that's a moderately large change, which I'd like to not block this change on if we can avoid it. But I think that's the right longer-term approach. Then here we would just need to find the lexically-enclosing `TranslationUnitDecl` for each template parameter and see if they're the same.
I found we could determine whether the declaration is in the current TU or not by using `Sema::ModuleScopes`, which contains the modules we're currently parsing.


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https://reviews.llvm.org/D118034