Fix include order in CXType.cpp

Handle template parameter-dependent bit field widths in libclang

In a class template, a bit field's width may depend on a template
parameter. In this case the width expression cannot be evaluated.

Previously clang_getFieldDeclBitWidth() would assert, or cause memory
unsafety and return an invalid result if assertions are disabled.

This adds a check for this case which returns an error code. An
additional function clang_isBitFieldDecl() is added to disambiguate
between error code meanings.

Fixes: #56644
Differential Revision: https://reviews.llvm.org/D130303

clang/docs/ReleaseNotes.rst

@@ -296,6 +296,11 @@ libclang
 - Introduced the new function ``clang_CXXMethod_isExplicit``,
   which identifies whether a constructor or conversion function cursor
   was marked with the explicit identifier.
+- Added check in ``clang_getFieldDeclBitWidth`` for whether a bit field
+  has an evaluable bit width. Fixes undefined behavior when called on a
+  bit field whose width depends on a template paramter.
+- Added function ``clang_isBitFieldDecl`` to check if a struct/class field is a
+  bit field.
 
 - Introduced the new ``CXIndex`` constructor function
   ``clang_createIndexWithOptions``, which allows overriding precompiled preamble

clang/include/clang-c/Index.h

@@ -3023,10 +3023,18 @@ CINDEX_LINKAGE long long clang_getEnumConstantDeclValue(CXCursor C);
 CINDEX_LINKAGE unsigned long long
 clang_getEnumConstantDeclUnsignedValue(CXCursor C);
 
+/**
+ * Returns non-zero if a field declaration has a bit width expression.
+ *
+ * If the cursor does not reference a bit field declaration 0 is returned.
+ */
+CINDEX_LINKAGE unsigned clang_isBitFieldDecl(CXCursor C);
+
 /**
  * Retrieve the bit width of a bit field declaration as an integer.
  *
- * If a cursor that is not a bit field declaration is passed in, -1 is returned.
+ * If the cursor does not reference a bit field, or if the bit field's width
+ * expression cannot be evaluated, -1 is returned.
  */
 CINDEX_LINKAGE int clang_getFieldDeclBitWidth(CXCursor C);
 

clang/tools/libclang/CXType.cpp

@@ -10,11 +10,11 @@
 //
 //===--------------------------------------------------------------------===//
 
+#include "CXType.h"
 #include "CIndexer.h"
 #include "CXCursor.h"
 #include "CXString.h"
 #include "CXTranslationUnit.h"
-#include "CXType.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/DeclTemplate.h"
@@ -371,14 +371,27 @@ unsigned long long clang_getEnumConstantDeclUnsignedValue(CXCursor C) {
   return ULLONG_MAX;
 }
 
+unsigned clang_isBitFieldDecl(CXCursor C) {
+  using namespace cxcursor;
+
+  if (clang_isDeclaration(C.kind)) {
+    const Decl *D = getCursorDecl(C);
+
+    if (const auto *FD = dyn_cast_or_null<FieldDecl>(D))
+      return FD->isBitField();
+  }
+
+  return 0;
+}
+
 int clang_getFieldDeclBitWidth(CXCursor C) {
   using namespace cxcursor;
 
   if (clang_isDeclaration(C.kind)) {
     const Decl *D = getCursorDecl(C);
 
-    if (const FieldDecl *FD = dyn_cast_or_null<FieldDecl>(D)) {
-      if (FD->isBitField())
+    if (const auto *FD = dyn_cast_or_null<FieldDecl>(D)) {
+      if (FD->isBitField() && !FD->getBitWidth()->isValueDependent())
         return FD->getBitWidthValue(getCursorContext(C));
     }
   }

clang/tools/libclang/libclang.map

@@ -422,6 +422,7 @@ LLVM_17 {
   global:
     clang_CXXMethod_isExplicit;
     clang_createIndexWithOptions;
+    clang_isBitFieldDecl;
 };
 
 # Example of how to add a new symbol version entry.  If you do add a new symbol