Fix for PR21254 - Assertion in comment parser

The size of the ID field in CommandInfo was narrow, leading to potential 
wrap-around of command IDs, causing misinterpretation later on.
The patch does the following:
- It extends the ID bitfield from 8 to 20 bits.
- It provides a DRY definition of the number of bits for the field to 
  avoid using literal numbers in different files.
- It introduces a new assertion that checks for the wrap-around.
- It adds the testcase from PR21254.

llvm-svn: 219802

1 files changed, 4 insertions, 0 deletions

diff --git a/clang/lib/AST/CommentCommandTraits.cpp b/clang/lib/AST/CommentCommandTraits.cpp
index a7b07a40c98..7378a7c3ac0 100644
--- a/clang/lib/AST/CommentCommandTraits.cpp
+++ b/clang/lib/AST/CommentCommandTraits.cpp
@@ -89,6 +89,10 @@ CommandInfo *CommandTraits::createCommandInfoWithName(StringRef CommandName) {
   // Value-initialize (=zero-initialize in this case) a new CommandInfo.
   CommandInfo *Info = new (Allocator) CommandInfo();
   Info->Name = Name;
+  // We only have a limited number of bits to encode command IDs in the
+  // CommandInfo structure, so the ID numbers can potentially wrap around.
+  assert((NextID < (1 << CommandInfo::NumCommandIDBits))
+         && "Too many commands. We have limited bits for the command ID.");
   Info->ID = NextID++;
 
   RegisteredCommands.push_back(Info);