add test.c and sketch query

Author: jeongsoolee09

c/misra/src/rules/RULE-6-2/SingleBitNamedBitFieldsOfASignedType.ql

@@ -13,7 +13,36 @@
 import cpp
 import codingstandards.c.misra
 
-from
+predicate isSigned(Type type) {
+  /* Check if it's a fixed number type, because declaring fixed number types like int8_t as 1 bit is obviously absurd */
+  type instanceof FixedWidthIntegralType or 
+/* Check if it's EXPLICITLY signed, because according to Rule 6.1, 'int' may be either signed or unsigned depending on the implementation. In the latter case, the query would lead to false positives. */
+  type instanceof IntegralType and
+  type.(IntegralType).isExplicitlySigned()
+}
+
+/* Check if the DECLARED bit-fields is a single bit, because Rule 6.2 also intends to catch confusion on the programmers' part. Consider:
+
+struct S {
+  int32_t x: 1;
+}
+
+In this case, field x is essentially of 32 bits, but is declared as 1 bit and its type int32_t is signed. Therefore, it indicates confusion by the programmer, which is exactly what this rule intends to find. */
+predicate isSingleBit(BitField bitField) {
+  bitField.getDeclaredNumBits() = 1
+}
+
+// predicate isNamedBitField(BitField bitField) {
+//   bitField.getName().length() != 0
+//   bitField.hasName(_)
+//   bitField.hasDefinition()
+//   wat
+// }
+
+from BitField bitField
 where
-  not isExcluded(x, TypesPackage::singleBitNamedBitFieldsOfASignedTypeQuery()) and
-select
+  not isExcluded(bitField, TypesPackage::singleBitNamedBitFieldsOfASignedTypeQuery()) and
+  isSingleBit(bitField) and // Single-bit,
+  // isNamedBitField(bitField) and // named,
+  isSigned(bitField.getType()) // but its type is signed.
+select bitField, "Single-bit bit-field named " + bitField.toString() + " has a signed type " + bitField.getType() + "."

c/misra/test/rules/RULE-6-2/test.c

@@ -0,0 +1,17 @@
+#include <stdint.h>
+
+struct SampleStruct {
+  int x1 : 1; // compilant: single-bit named field without signed declaration
+  signed int x2 : 1; // non_compilant: single-bit named field with a signed type
+  signed char
+      x3 : 1; // non_compilant: single-bit named field with a signed type
+  signed short
+      x4 : 1; // non_compilant: single-bit named field with a signed type
+  unsigned int
+      x5 : 1; // compilant: single-bit named field but with an unsigned type
+  signed int x6 : 2; // compilant: named field with a signed type but declared
+                     // to carry more than 1 bit
+  int32_t x7 : 1;  // non_compilant: single-bit named field that has single-bit
+                   // bit-field, even though technically it has 32 bits
+  signed char : 1; // compilant: single-bit bit-field but unnamed
+} sample_struct;