[clang] ad7211d - [clang] fix undefined behaviour in RawComment::getFormattedText()

[Raphael Isemann via cfe-commits]

Author: Oliver Bruns
Date: 2020-04-06T10:48:25+02:00
New Revision: ad7211df6f257e39da2e5a11b2456b4488f32a1e

URL: https://github.com/llvm/llvm-project/commit/ad7211df6f257e39da2e5a11b2456b4488f32a1e
DIFF: https://github.com/llvm/llvm-project/commit/ad7211df6f257e39da2e5a11b2456b4488f32a1e.diff

LOG: [clang] fix undefined behaviour in RawComment::getFormattedText()

Summary:
Calling `back()` and `pop_back()` on the empty string is undefined
behavior [1,2].

The issue manifested itself as an uncaught `std::out_of_range` exception
when running `clangd` compiled on RHEL7 using devtoolset-9.

[1] https://en.cppreference.com/w/cpp/string/basic_string/back
[2] https://en.cppreference.com/w/cpp/string/basic_string/pop_back

Fixes: 1ff7c32fc91c607b690d4bb9cf42f406be8dde68

Reviewers: teemperor, ioeric, cfe-commits

Reviewed By: teemperor

Subscribers: ilya-biryukov, kadircet, usaxena95

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77468

Added: 
    

Modified: 
    clang/lib/AST/RawCommentList.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/RawCommentList.cpp b/clang/lib/AST/RawCommentList.cpp
index 8552b4fcd2b3..a8d15036cab9 100644
--- a/clang/lib/AST/RawCommentList.cpp
+++ b/clang/lib/AST/RawCommentList.cpp
@@ -431,7 +431,7 @@ std::string RawComment::getFormattedText(const SourceManager &SourceMgr,
   };
 
   auto DropTrailingNewLines = [](std::string &Str) {
-    while (Str.back() == '\n')
+    while (!Str.empty() && Str.back() == '\n')
       Str.pop_back();
   };