From 50c43e228542cc1b211c9b2dd6e50cc1ea7b002a Mon Sep 17 00:00:00 2001
From: Michael Tautschnig <tautschn@amazon.com>
Date: Sun, 9 Oct 2022 13:58:55 +0000
Subject: [PATCH] C front-end: zero-width bit-fields must not have a declarator

The C standard forbids this and compilers rightly reject this.
---
 regression/ansi-c/bitfields2/main.c    | 39 ++++++++++++++++++++++++++
 regression/ansi-c/bitfields2/test.desc |  9 ++++++
 src/ansi-c/c_typecheck_type.cpp        | 10 +++++++
 3 files changed, 58 insertions(+)
 create mode 100644 regression/ansi-c/bitfields2/main.c
 create mode 100644 regression/ansi-c/bitfields2/test.desc

diff --git a/regression/ansi-c/bitfields2/main.c b/regression/ansi-c/bitfields2/main.c
new file mode 100644
index 00000000000..03e71366971
--- /dev/null
+++ b/regression/ansi-c/bitfields2/main.c
@@ -0,0 +1,39 @@
+#include <limits.h>
+
+#define CONCAT(a, b) a##b
+#define CONCAT2(a, b) CONCAT(a, b)
+
+#define STATIC_ASSERT(condition)                                               \
+  int CONCAT2(some_array, __LINE__)[(condition) ? 1 : -1]
+
+#if CHAR_BIT == 8
+struct bits
+{
+  char a : 4;
+  char b : 4;
+  char c : 4;
+  char d : 4;
+  char : 0; // this is ok: no declarator
+  int i;
+};
+
+STATIC_ASSERT(sizeof(struct bits) == 2 * sizeof(int));
+
+#  pragma pack(1)
+struct packed_bits
+{
+  char a : 4;
+  char b : 4;
+  char c : 4;
+  char d : 4;
+  char x : 0; // this is not permitted
+  int i;
+};
+#  pragma pack()
+
+STATIC_ASSERT(sizeof(struct packed_bits) == sizeof(int) + 2);
+#endif
+
+int main()
+{
+}
diff --git a/regression/ansi-c/bitfields2/test.desc b/regression/ansi-c/bitfields2/test.desc
new file mode 100644
index 00000000000..1fd6f840e01
--- /dev/null
+++ b/regression/ansi-c/bitfields2/test.desc
@@ -0,0 +1,9 @@
+CORE
+main.c
+
+zero-width bit-field with declarator not permitted$
+CONVERSION ERROR
+^EXIT=(64|1)$
+^SIGNAL=0$
+--
+^warning: ignoring
diff --git a/src/ansi-c/c_typecheck_type.cpp b/src/ansi-c/c_typecheck_type.cpp
index 42fdd048577..bde69b633b7 100644
--- a/src/ansi-c/c_typecheck_type.cpp
+++ b/src/ansi-c/c_typecheck_type.cpp
@@ -964,6 +964,16 @@ void c_typecheck_baset::typecheck_compound_body(
           throw 0;
         }
 
+        if(
+          new_component.type().id() == ID_c_bit_field &&
+          to_c_bit_field_type(new_component.type()).get_width() == 0 &&
+          !new_component.get_name().empty())
+        {
+          throw invalid_source_file_exceptiont{
+            "zero-width bit-field with declarator not permitted",
+            source_location};
+        }
+
         components.push_back(new_component);
       }
     }