Add clang_CXXMethod_isExplicit to libclang

The new method is a wrapper of `CXXConstructorDecl::isExplicit` and
`CXXConversionDecl::isExplicit`, allowing the user to recognize whether
the declaration pointed to by a cursor was marked with the explicit
specifier.

An export for the function, together with its documentation, was added
to "clang/include/clang-c/Index.h" with an implementation provided in
"clang/tools/libclang/CIndex.cpp".

The implementation is based on similar `clang_CXXMethod`
implementations, returning a falsy unsigned value when the cursor is not
a declaration, is not a declaration for a constructor or conversion
function or is not a relevant declaration that was marked with the
`explicit` specifier.

The new symbol was added to "clang/tools/libclang/libclang.map" to be
exported, under the LLVM16 tag.

"clang/tools/c-index-test/c-index-test.c" was modified to print a
specific tag, "(explicit)", for cursors that are recognized by
`clang_CXXMethod_isExplicit`.

Two new regression files, "explicit-constructor.cpp" and
"explicit-conversion-function.cpp", were added to "clang/test/Index", to
ensure that the behavior of the new function is correct for constructors
and conversion functions, respectively.

The "get-cursor.cpp", "index-file.cpp" and
"recursive-cxx-member-calls.cpp" regression files in "clang/test/Index"
were updated as they were affected by the new "(explicit)" tag.

A binding for the new function was added to libclang's python's
bindings, in "clang/bindings/python/clang/cindex.py", as the
"is_explicit_method" method under `Cursor`.

An accompanying test was added to
"clang/bindings/python/tests/cindex/test_cursor.py", mimicking the
regression tests for the C side.

The current release note for Clang, "clang/docs/ReleaseNotes.rst" was
modified to report the new addition under the "libclang" section.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D140756

1 files changed, 2 insertions, 0 deletions

diff --git a/clang/tools/c-index-test/c-index-test.c b/clang/tools/c-index-test/c-index-test.c
index cc425fc..983738d 100644
--- a/clang/tools/c-index-test/c-index-test.c
+++ b/clang/tools/c-index-test/c-index-test.c
@@ -916,6 +916,8 @@ static void PrintCursor(CXCursor Cursor, const char *CommentSchemaFile) {
       printf(" (copy-assignment operator)");
     if (clang_CXXMethod_isMoveAssignmentOperator(Cursor))
       printf(" (move-assignment operator)");
+    if (clang_CXXMethod_isExplicit(Cursor))
+      printf(" (explicit)");
     if (clang_CXXRecord_isAbstract(Cursor))
       printf(" (abstract)");
     if (clang_EnumDecl_isScoped(Cursor))