[clang] [clang-format] Fix crashes when the macro expansion is empty (PR #119428)

[via cfe-commits]

https://github.com/amane-ame created https://github.com/llvm/llvm-project/pull/119428

An empty expansion should be valid, like `echo 'A()' | clang-format --style='{Macros: [A(x)=x]}'`
See #119258.

>From 3a4c1a924faef3a7a09126694fcb943bd7083451 Mon Sep 17 00:00:00 2001
From: amane-ame <i at amane-a.me>
Date: Wed, 11 Dec 2024 02:13:43 +0800
Subject: [PATCH] Fix crashes when the macro expansion is empty

---
 clang/lib/Format/MacroExpander.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/clang/lib/Format/MacroExpander.cpp b/clang/lib/Format/MacroExpander.cpp
index fd2a16894d643d..ed9e51dfbfef1f 100644
--- a/clang/lib/Format/MacroExpander.cpp
+++ b/clang/lib/Format/MacroExpander.cpp
@@ -233,6 +233,10 @@ MacroExpander::expand(FormatToken *ID,
   if (Result.size() > 1) {
     ++Result[0]->MacroCtx->StartOfExpansion;
     ++Result[Result.size() - 2]->MacroCtx->EndOfExpansion;
+  } else {
+    // If the macro expansion is empty, mark the start and end
+    Result[0]->MacroCtx->StartOfExpansion = 1;
+    Result[0]->MacroCtx->EndOfExpansion = 1;
   }
   return Result;
 }