[Clang] Fix a Wbitfield-enum-conversion warning in DirectoryLookup.h

[xgupta]

Summary

When compiling clang/Lex/DirectoryLookup.h with option -Wbitfield-enum-conversion, we get the following warning:

DirectoryLookup.h:77:17: warning:

bit-field 'DirCharacteristic' is not wide enough to store all enumerators of
'CharacteristicKind' [-Wbitfield-enum-conversion]
: u(Map), DirCharacteristic(DT), LookupType(LT_HeaderMap),

DirCharacteristic is a bitfield with 2 bits (4 values)

/// DirCharacteristic - The type of directory this is: this is an instance of
/// SrcMgr::CharacteristicKind.
unsigned DirCharacteristic : 2;

Whereas SrcMgr::CharacterKind is an enum with 5 values:
enum CharacteristicKind {

C_User,
C_System,
C_ExternCSystem,
C_User_ModuleMap,
C_System_ModuleMap

};

Solution is to increase DirCharacteristic bitfield from 2 to 3.
Patch by Dimitri van Heesch

[aaron.ballman]

LGTM but can you find a test case that would show we don't regress this in the future?

[xgupta]

In D142304#4073573, @aaron.ballman wrote:

LGTM but can you find a test case that would show we don't regress this in the future?

I haven't found the test case, but I found a commit that increases CharacteristicKind enum's values from 3 to 5. Seems they missed updating DirCharacteristic. Do you have suggestions on where/how to add a test case for this?

[aaron.ballman]

I looked through the code base and I think this fix is good but benign (it doesn't look like it'll impact anything that I can see). So LGTM without tests.

[xgupta]

In D142304#4074211, @aaron.ballman wrote:

I looked through the code base and I think this fix is good but benign (it doesn't look like it'll impact anything that I can see). So LGTM without tests.

Thank you for reviewing the change.

clang/include/clang/Lex/DirectoryLookup.h

union DLU { // This union is discriminated by isHeaderMap.
     const HeaderMap *Map;
 
     DLU(DirectoryEntryRef Dir) : Dir(Dir) {}
     DLU(const HeaderMap *Map) : Map(Map) {}
   } u;
 
   /// DirCharacteristic - The type of directory this is: this is an instance of
   /// SrcMgr::CharacteristicKind.
-  unsigned DirCharacteristic : 2;
+  unsigned DirCharacteristic : 3;
 
   /// LookupType - This indicates whether this DirectoryLookup object is a
   /// normal directory, a framework, or a headermap.
   unsigned LookupType : 2;
 
   /// Whether this is a header map used when building a framework.
   unsigned IsIndexHeaderMap : 1;