Fix RULE-7-0-4 false positives for non-built-in operators

[castler]

Description

InappropriateBitwiseOrShiftOperands.ql reported operations that do not use the built-in bitwise or shift operators, most notably the stream insertion and extraction operators, e.g. stream << value.

Resolved calls to a user provided operator are modelled as FunctionCalls and therefore never reach this query. The reported operations were instead the syntactic LShiftExpr/RShiftExpr nodes emitted for uninstantiated template bodies, where the operands are either unresolved (unknown, auto &&) or are the non-dependent result of an already resolved overload, such as std::basic_ostream<char, std::char_traits<char>> &.

The built-in bitwise and shift operators are only applicable to integral and unscoped enumeration operands, so an operation with an operand of any other type does not use them. The query now requires both operands to be of such a type before reporting a violation.

This does not introduce false negatives for dependent operands, because the template instantiations, in which the operand types are known, are still reported.

Fixes #1177

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• Are the alert messages properly formatted and consistent with the style guide?
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  As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.
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[MichaelRFairhurst]

Thank you @castler! I remember seeing a lot of these, but I had filed a deviation and then forgot. Thank you for the fixes!

Great analysis of the FP, nicely done, very subtle and good catch!

In general, we often use not thing.isFromUninstantiatedTemplate(_), and I think that would make sense for this. Technically this may mean we don't report warnings in uninstantiated template code where we otherwise could have...but uninstantiated template code analysis is generally tricky to get right, as you've seen here.

Adding not x.isFromUninstantiatedTemplate(_) seems to fix most FP cases. The remaining FPs from here I see in my databases are:

• decltype(declval<std::ostream &>() << std::declval<T const &>()) for some reason still is a BinaryShiftExpr
• unsigned __int128 shifts
• unscoped enums without explicit types e.g. enum e { ... }
• char32_t

Your version solves those decltype FPs, which is great. Note for unscoped enums, the standard says to treat them as their explicit underlying type if specified. For unscoped enums with no explicit type they should be ignored and are covered by rule 10.2.3.

For isBuiltInOperandType, I think we should prefer to use expr instanceof MisraCpp23BuiltInTypes::MisraBuiltInType, which should handle all the various cases well related to enums, typedefs, decltypes, references, specifiers, etc.

This makes me wonder what our query missed, since we're already using that module ourselves... It looks like the general mistake we made in this query is using not ...::isUnsignedType(type) instead of ...::isSignedType(type) (without the not). For something like a user defined class, ...::is[Un]SignedType(classType) is false, and therefore not ...::is[Un]SignedType(classType) is always true, and that's a wider net than we want to cast.

So the query could then look something like:

from Expr x, string message
where
  not isExcluded(x, ...) and
  not x.isFromUninstantiatedTemplate(_) and
  x instanceof MisraCpp23BuiltinTypes::MisraBuiltInType and

This would only leaves FPs for:

• char32_t
• unsigned __int128

The char32_t FP is caused by a bug in MisraCpp23BuiltInTypes::NumericTypes::getSignedness() -- we should have also added getSignedness() to CharacterType.

Alternatively, instead of x instanceof MisraCpp23BuiltinType::MisraBuiltInType, you could update everything to:

   ...
   MisraCpp23BiltInTypes::isSignedType(opType) and
   ...

This would fix the char32_t case by excluding them from analysis...which is sort of incidentally correct because the char_x_ts are always unsigned.

If my analysis seems right to you, and I haven't missed anything, then feel free to solve with whatever approach resonates with you!