[clang] [libclang] Add functions to query template parameters and fix parameter pack handling (PR #183504)

[via cfe-commits]

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@@ -3267,7 +3267,29 @@ CINDEX_LINKAGE CXType clang_Cursor_getTemplateArgumentType(CXCursor C,
                                                            unsigned I);
 
 /**
- * Retrieve the value of an Integral TemplateArgument (of a function
+ * Retrieve the type of an Integral TemplateArgument at a given index.
+ *
+ * For example, for:
+ *   template <typename T, int N>
+ *   void foo() {}
+ *
+ *   template <>
+ *   void foo<float, 42>();
+ *
+ * If called with I = 1, the type "int" will be returned (the type of the
+ * integral argument 42). An invalid type is returned if the argument at
+ * index I is not integral, or if the index is out of range.
+ *
+ * \param C a cursor representing a template specialization.
+ * \param I the zero-based index of the template argument.
+ *
+ * \returns the type of the integral template argument, or an invalid type.
+ */
+CINDEX_LINKAGE CXType clang_Cursor_getTemplateArgumentIntegralType(CXCursor C,
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fscheidl wrote:

My earlier reasoning was that a type template argument is a type, while a non-type template argument has a type. Since these are different semantic operations, my intuition was to not put them in the same accessor.

In the original proposal `clang_Cursor_getTemplateArgumentIntegralType` returns the type after conversion (so it's actually `short` in your example, not `int`) which is indeed the type of the NTTP, not the type of the expression that is passed as argument. So `clang_Cursor_getNonTypeTemplateArgumentType` (or whatever we call it) would really be returning the parameter type for non-type arguments, which is definitely worth being precise about in the docs (and naming!).

FWIW The function argument accessors like `clang_getNumArgTypes` and `clang_getArgType` might invite a similar discussion, since they actually refer to function parameters and not the passed arguments.

Happy to wait for @erichkeane's input on the naming/semantics.

https://github.com/llvm/llvm-project/pull/183504