[clang] [C++20][Modules] Implement P1857R3 Modules Dependency Discovery (PR #107168)

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@@ -142,6 +142,15 @@ void printDependencyDirectivesAsSource(
 /// \returns true if any C++20 named modules related directive was found.
 bool scanInputForCXX20ModulesUsage(StringRef Source);
 
+/// Scan an input source buffer, and check whether the input ssource is a
+/// preprocessed output.
+///
+/// \param Source The input source buffer.
+///
+/// \returns true if any '__preprocessed_module' or '__preprocessed_import'
+/// directive was found.
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yronglin wrote:

Thanks for pointing out this! I have fixed this and added a test.

https://github.com/llvm/llvm-project/pull/107168