From 48fb6659610a3177e8606681046dfa0d19f67203 Mon Sep 17 00:00:00 2001
From: Collin Baker <collinbaker@chromium.org>
Date: Tue, 14 Mar 2023 09:57:44 -0400
Subject: [PATCH] [libclang] No longer attempt to get a dependent bit-width

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.

This work was largely taken from an earlier patch which was reverted
due to an accidental API duplication
(https://reviews.llvm.org/D130303).

Fixes: https://github.com/llvm/llvm-project/issues/56644
Co-authored-by: Aaron Ballman <aaron@aaronballman.com>
Differential Revision: https://reviews.llvm.org/D146039
---
 clang/docs/ReleaseNotes.rst     |  4 ++++
 clang/include/clang-c/Index.h   | 26 ++++++++++++++++++--------
 clang/tools/libclang/CXType.cpp |  4 ++--
 3 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst clang/docs/ReleaseNotes.rst
index cfec4ed96ad9bf9..66a9210c35b6610 100644
--- a/clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -315,6 +315,10 @@ libclang
   ``clang_CXIndex_setInvocationEmissionPathOption`` in favor of the new
   function ``clang_createIndexWithOptions`` in order to improve thread safety.
 
+- 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.
+
 Static Analyzer
 ---------------
 - Fix incorrect alignment attribute on the this parameter of certain
diff --git a/clang/include/clang-c/Index.h clang/include/clang-c/Index.h
index bc9e100846be699..710668740e0e6f6 100644
--- a/clang/include/clang-c/Index.h
+++ clang/include/clang-c/Index.h
@@ -3029,9 +3029,25 @@ CINDEX_LINKAGE unsigned long long
 clang_getEnumConstantDeclUnsignedValue(CXCursor C);
 
 /**
- * Retrieve the bit width of a bit field declaration as an integer.
+ * Returns non-zero if the cursor specifies a Record member that is a bit-field.
+ */
+CINDEX_LINKAGE unsigned clang_Cursor_isBitField(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.
+ *
+ * For example:
+ * \code
+ * if (clang_Cursor_isBitField(Cursor)) {
+ *   int Width = clang_getFieldDeclBitWidth(Cursor);
+ *   if (Width != -1) {
+ *     // The bit-field width is not value-dependent.
+ *   }
+ * }
+ * \endcode
  */
 CINDEX_LINKAGE int clang_getFieldDeclBitWidth(CXCursor C);
 
@@ -3660,12 +3676,6 @@ CINDEX_LINKAGE CXType clang_Type_getTemplateArgumentAsType(CXType T,
  */
 CINDEX_LINKAGE enum CXRefQualifierKind clang_Type_getCXXRefQualifier(CXType T);
 
-/**
- * Returns non-zero if the cursor specifies a Record member that is a
- *   bitfield.
- */
-CINDEX_LINKAGE unsigned clang_Cursor_isBitField(CXCursor C);
-
 /**
  * Returns 1 if the base class specified by the cursor with kind
  *   CX_CXXBaseSpecifier is virtual.
diff --git a/clang/tools/libclang/CXType.cpp clang/tools/libclang/CXType.cpp
index a1d157c63995b14..eb8bfc25a7c9106 100644
--- a/clang/tools/libclang/CXType.cpp
+++ 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"
@@ -378,7 +378,7 @@ int clang_getFieldDeclBitWidth(CXCursor C) {
     const Decl *D = getCursorDecl(C);
 
     if (const FieldDecl *FD = dyn_cast_or_null<FieldDecl>(D)) {
-      if (FD->isBitField())
+      if (FD->isBitField() && !FD->getBitWidth()->isValueDependent())
         return FD->getBitWidthValue(getCursorContext(C));
     }
   }