RULE-10-4: Improve essential type detection

c/misra/src/codingstandards/c/misra/EssentialTypes.qll

@@ -130,12 +130,17 @@ EssentialTypeCategory getEssentialTypeCategory(Type type) {
     essentialType.(IntegralType).isSigned() and
     not essentialType instanceof PlainCharType
     or
+    // Anonymous enums are considered to be signed
+    result = EssentiallySignedType() and
+    essentialType instanceof AnonymousEnumType and
+    not essentialType instanceof MisraBoolType
+    or
     result = EssentiallyUnsignedType() and
     essentialType.(IntegralType).isUnsigned() and
     not essentialType instanceof PlainCharType
     or
     result = EssentiallyEnumType() and
-    essentialType instanceof Enum and
+    essentialType instanceof NamedEnumType and
     not essentialType instanceof MisraBoolType
     or
     result = EssentiallyFloatingType() and
@@ -348,16 +353,51 @@ class EssentialBinaryArithmeticExpr extends EssentialExpr, BinaryArithmeticOpera
   }
 }
 
+/**
+ * A named Enum type, as per D.5.
+ */
+class NamedEnumType extends Enum {
+  NamedEnumType() {
+    not isAnonymous()
+    or
+    exists(Type useOfEnum | this = useOfEnum.stripType() |
+      exists(TypedefType t | t.getBaseType() = useOfEnum)
+      or
+      exists(Function f | f.getType() = useOfEnum or f.getAParameter().getType() = useOfEnum)
+      or
+      exists(Struct s | s.getAField().getType() = useOfEnum)
+      or
+      exists(Variable v | v.getType() = useOfEnum)
+    )
+  }
+}
+
+/**
+ * An anonymous Enum type, as per D.5.
+ */
+class AnonymousEnumType extends Enum {
+  AnonymousEnumType() { not this instanceof NamedEnumType }
+}
+
+/**
+ * The EssentialType of an EnumConstantAccess, which may be essentially enum or essentially signed.
+ */
 class EssentialEnumConstantAccess extends EssentialExpr, EnumConstantAccess {
-  override Type getEssentialType() { result = getTarget().getDeclaringEnum() }
+  override Type getEssentialType() {
+    exists(Enum e | e = getTarget().getDeclaringEnum() |
+      if e instanceof NamedEnumType then result = e else result = stlr(this)
+    )
+  }
 }
 
 class EssentialLiteral extends EssentialExpr, Literal {
   override Type getEssentialType() {
     if this instanceof BooleanLiteral
-    then result instanceof MisraBoolType
+    then
+      // This returns a multitude of types - not sure if we really want that
+      result instanceof MisraBoolType
     else (
-      if this.(CharLiteral).getCharacter().length() = 1
+      if this instanceof CharLiteral
       then result instanceof PlainCharType
       else
         exists(Type underlyingStandardType |

c/misra/src/rules/RULE-10-4/OperandsWithMismatchedEssentialTypeCategory.ql

@@ -38,7 +38,7 @@ where
     // be reported as non-compliant.
     leftOpTypeCategory = EssentiallyEnumType() and
     rightOpTypeCategory = EssentiallyEnumType() and
-    not leftOpEssentialType = rightOpEssentialType and
+    not leftOpEssentialType.getUnspecifiedType() = rightOpEssentialType.getUnspecifiedType() and
     message =
       "The operands of this operator with usual arithmetic conversions have mismatched essentially Enum types (left operand: "
         + leftOpEssentialType + ", right operand: " + rightOpEssentialType + ")."

c/misra/test/c/misra/EssentialTypes.expected

@@ -1,3 +1,9 @@
+| file://:0:0:0:0 | 0 | signed char | signed char | essentially Signed type |
+| file://:0:0:0:0 | 0 | signed char | signed char | essentially Signed type |
+| file://:0:0:0:0 | 0 | signed char | signed char | essentially Signed type |
+| file://:0:0:0:0 | 0 | signed char | signed char | essentially Signed type |
+| file://:0:0:0:0 | 0 | signed char | signed char | essentially Signed type |
+| file://:0:0:0:0 | 0 | signed char | signed char | essentially Signed type |
 | test.c:4:20:4:20 | 1 | signed char | signed char | essentially Signed type |
 | test.c:4:20:4:20 | (unsigned int)... | unsigned int | unsigned int | essentially Unsigned type |
 | test.c:5:23:5:23 | 1 | signed char | signed char | essentially Signed type |
@@ -73,3 +79,14 @@
 | test.c:54:3:54:5 | ~ ... | int | int | essentially Signed type |
 | test.c:54:4:54:5 | (int)... | int | int | essentially Signed type |
 | test.c:54:4:54:5 | ss | signed short | signed short | essentially Signed type |
+| test.c:63:30:63:32 | ((unnamed enum))... | (unnamed enum) | (unnamed enum) | essentially Enum Type |
+| test.c:63:30:63:32 | EC5 | (unnamed enum) | (unnamed enum) | essentially Enum Type |
+| test.c:70:3:70:5 | EC1 | signed char | signed char | essentially Signed type |
+| test.c:71:3:71:5 | EC2 | E1 | E1 | essentially Enum Type |
+| test.c:72:3:72:5 | EC3 | (unnamed enum) | (unnamed enum) | essentially Enum Type |
+| test.c:73:3:73:5 | EC4 | (unnamed enum) | (unnamed enum) | essentially Enum Type |
+| test.c:74:3:74:5 | EC5 | (unnamed enum) | (unnamed enum) | essentially Enum Type |
+| test.c:75:3:75:5 | EC6 | (unnamed enum) | (unnamed enum) | essentially Enum Type |
+| test.c:79:3:79:5 | 97 | char | char | essentially Character type |
+| test.c:80:3:80:6 | 10 | char | char | essentially Character type |
+| test.c:81:3:81:6 | 0 | char | char | essentially Character type |

c/misra/test/c/misra/test.c

@@ -52,4 +52,31 @@ void testUnary() {
   ~us; // Should be essentially unsigned
   ~s;  // Should be essentially signed
   ~ss; // Should be essentially signed
+}
+
+enum { EC1 };
+enum E1 { EC2 };
+typedef enum { EC3 } E2;
+
+enum { EC4 } g;
+
+enum { EC5 } test() { return EC5; }
+
+struct S1 {
+  enum { EC6 } m;
+};
+
+void testEnums() {
+  EC1; // Should be essentially signed
+  EC2; // Should be essentially enum
+  EC3; // Should be essentially enum
+  EC4; // Should be essentially enum
+  EC5; // Should be essentially enum
+  EC6; // Should be essentially enum
+}
+
+void testControlChar() {
+  'a';  // Essentially char
+  '\n'; // Essentially char
+  '\0'; // Essentially char
 }

c/misra/test/rules/RULE-10-4/test.c

@@ -33,4 +33,13 @@ void testOps() {
   A < A;     // COMPLIANT
   e1a < e2a; // NON_COMPLIANT
   A < D;     // NON_COMPLIANT
+
+  enum { G };
+  s32 + G;   // COMPLIANT
+  c == '\n'; // COMPLIANT
+
+  typedef enum { H } E3;
+
+  E3 e3a = H;
+  e3a < H; // COMPLIANT
 }

change_notes/2024-10-15-lits-and-constants-10-4.md

@@ -0,0 +1,5 @@
+ - `RULE-10-4` - `OperandswithMismatchedEssentialTypeCategory.ql`:
+   - Removed false positives where a specified or typedef'd enum type was compared to an enum constant type.
+ - `EssentialType` - for all queries related to essential types:
+   - `\n` and other control characters are now correctly deduced as essentially char type, instead of an essentially integer type.
+   - Enum constants for anonymous enums are now correctly deduced as an essentially signed integer type instead of essentially enum.