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

[Vlad Serebrennikov via cfe-commits]

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@@ -0,0 +1,58 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -std=c++20 %t/cwg2947_example1.cpp -D'DOT_BAR=.bar' -fsyntax-only -verify
+// RUN: %clang_cc1 -std=c++20 %t/cwg2947_example2.cpp -D'MOD_ATTR=[[vendor::shiny_module]]' -fsyntax-only -verify
+// RUN: %clang_cc1 -std=c++20 %t/cwg2947_example3.cpp -fsyntax-only -verify
+// RUN: %clang_cc1 -std=c++20 %t/cwg2947_example4.cpp -fsyntax-only -verify
+// RUN: %clang_cc1 -std=c++20 %t/cwg2947_example5.cpp -fsyntax-only -verify
+// RUN: %clang_cc1 -std=c++20 %t/cwg2947_example6.cpp -fsyntax-only -verify
+// RUN: %clang_cc1 -std=c++20 %t/cwg2947_ext1.cpp -verify -E | FileCheck %t/cwg2947_ext1.cpp
+// RUN: %clang_cc1 -std=c++20 %t/cwg2947_ext2.cpp -fsyntax-only -verify
+// RUN: %clang_cc1 -std=c++20 %t/cwg2947_ext3.cpp -fsyntax-only -verify
+
+//--- cwg2947_example1.cpp
+// #define DOT_BAR .bar
+export module foo DOT_BAR; // error: expansion of DOT_BAR; does not begin with ; or [
+// expected-error at -1 {{unexpected preprocessing token '.' after module name, only ';' and '[' (start of attribute specifier sequence) are allowed}}
+
+//--- cwg2947_example2.cpp
+export module M MOD_ATTR;        // OK
+// expected-warning at -1 {{unknown attribute 'vendor::shiny_module' ignored}}
+
+//--- cwg2947_example3.cpp
+export module a
+  .b;                         // error: preprocessing token after pp-module-name is not ; or [
+// expected-error at -1 {{unexpected preprocessing token '.' after module name, only ';' and '[' (start of attribute specifier sequence) are allowed}}
+
+//--- cwg2947_example4.cpp
+export module M [[
+  attr1,
+  attr2 ]] ;                 // OK
+// expected-warning at -2 {{unknown attribute 'attr1' ignored}}
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Endilll wrote:

Can you move this up right below `attr1`, so that `expected-warning at -1` works?

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