[-Wunsafe-buffer-usage] Explicitly unsupport fixits for multidimensional C arrays

Proper support for multidimensional arrays is outside of the scope of
initial std::array fixits.
This change makes sure that we don't accidentally emit fixits for multidimensional
arrays until that work is all done. It adds a specific check when transforming
VarDecl type to std::array. Also adds corresponding several testscases.

Author: jkorous-apple

clang/lib/Analysis/UnsafeBufferUsage.cpp

@@ -19,6 +19,7 @@
 #include "llvm/ADT/APSInt.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Casting.h"
 #include <memory>
 #include <optional>
 #include <queue>
@@ -2477,6 +2478,9 @@ static FixItList fixVarDeclWithArray(const VarDecl *D, const ASTContext &Ctx,
   if (auto CAT = dyn_cast<clang::ConstantArrayType>(D->getType())) {
     const QualType &ArrayEltT = CAT->getElementType();
     assert(!ArrayEltT.isNull() && "Trying to fix a non-array type variable!");
+    // FIXME: support multi-dimensional arrays
+    if (isa<clang::ConstantArrayType>(ArrayEltT))
+      return {};
 
     const SourceLocation IdentifierLoc = getVarDeclIdentifierLoc(D);
 

clang/test/SemaCXX/warn-unsafe-buffer-usage-fixits-local-var-array.cpp

@@ -10,6 +10,32 @@ void simple(unsigned idx) {
   buffer[idx] = 0;
 }
 
+void array2d(unsigned idx) {
+  int buffer[10][10];
+// CHECK-NOT: fix-it:"{{.*}}":{[[@LINE-1]]
+  buffer[idx][idx] = 0;
+}
+
+void array2d_assign_from_elem(unsigned idx) {
+  int buffer[10][10];
+// CHECK-NOT: fix-it:"{{.*}}":{[[@LINE-1]]
+  int a = buffer[idx][idx];
+}
+
+void array2d_use(unsigned);
+void array2d_call(unsigned idx) {
+  int buffer[10][10];
+// CHECK-NOT: fix-it:"{{.*}}":{[[@LINE-1]]
+  array2d_use(buffer[idx][idx]);
+}
+
+void array2d_typedef(unsigned idx) {
+  typedef int ten_ints_t[10];
+  ten_ints_t buffer[10];
+// CHECK-NOT: fix-it:"{{.*}}":{[[@LINE-1]]
+  buffer[idx][idx] = 0;
+}
+
 void whitespace_in_declaration(unsigned idx) {
   int      buffer_w   [       10 ];
 // CHECK: fix-it:"{{.*}}":{[[@LINE-1]]:3-[[@LINE-1]]:35}:"std::array<int, 10> buffer_w"