[clang][Preprocessor] Add peekNextPPToken, makes look ahead next token without side-effects (#143898)

This PR introduce a new function `peekNextPPToken`. It's an extension of
`isNextPPTokenLParen` and can makes look ahead one token in preprocessor
without side-effects.

It's also the 1st part of
https://github.com/llvm/llvm-project/pull/107168 and it was used to look
ahead next token then determine whether current lexing pp directive is
one of pp-import or pp-module directive.

At the start of phase 4 an import or module token is treated as starting
a directive and are converted to their respective keywords iff:

 - After skipping horizontal whitespace are
    - at the start of a logical line, or
    - preceded by an export at the start of the logical line.
- Are followed by an identifier pp token (before macro expansion), or
    - <, ", or : (but not ::) pp tokens for import, or
    - ; for module
Otherwise the token is treated as an identifier.

---------

Signed-off-by: yronglin <yronglin777@gmail.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 18b2f5f..7fecbe9 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -813,14 +813,14 @@ bool Preprocessor::HandleIdentifier(Token &Identifier) {
       if (!Identifier.isExpandDisabled() && MI->isEnabled()) {
         // C99 6.10.3p10: If the preprocessing token immediately after the
         // macro name isn't a '(', this macro should not be expanded.
-        if (!MI->isFunctionLike() || isNextPPTokenLParen())
+        if (!MI->isFunctionLike() || isNextPPTokenOneOf<tok::l_paren>())
           return HandleMacroExpandedIdentifier(Identifier, MD);
       } else {
         // C99 6.10.3.4p2 says that a disabled macro may never again be
         // expanded, even if it's in a context where it could be expanded in the
         // future.
         Identifier.setFlag(Token::DisableExpand);
-        if (MI->isObjectLike() || isNextPPTokenLParen())
+        if (MI->isObjectLike() || isNextPPTokenOneOf<tok::l_paren>())
           Diag(Identifier, diag::pp_disabled_macro_expansion);
       }
     }