[clang] [HLSL] Implement `export` keyword (PR #96823)

[Helena Kotas via cfe-commits]

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@@ -0,0 +1,56 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -x hlsl -o - %s -verify
+
+export void f1();
+
+export void f1() {}
+
+namespace { // expected-note {{anonymous namespace begins here}}
+    export void f2(); // expected-error {{export declaration appears within anonymous namespace}}
+}
+
+export void f3();
+
+export { // expected-note {{export block begins here}}
+    void f4() {}
+    export void f5() {} // expected-error {{export declaration appears within another export declaration}}
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hekota wrote:

Each export creates a new ExportDecl node in the AST three and limiting it to just one make it cleaner. I am not aware of any specific reason other than maybe this and to keep the syntax and parsing code identical to C++ modules export.

https://github.com/llvm/llvm-project/pull/96823