bugprone-narrowing-conversions false positive for contional expression (in C)

[AndreyG]

char test(int cond, char c) {
	char ret = cond > 0 ? ':' : c; // warning: narrowing conversion from 'int' to signed type 'char' is implementation-defined
	return ret;
}

https://godbolt.org/z/6P8Yaqn4o

[pinskia]

Well in C the type of a character literal is int ...
So typeof(cond > 0 ? ':' : c) will be int.

[AndreyG]

So typeof(cond > 0 ? ':' : c) will be int.

Yes, but because we know that both arguments of the conditional expression could be converted to char without narrowing, then the whole expression could be converted to char without narrowing. Moreover the check of conditional expression is already implemented in terms of the separate checks of arguments:

llvm-project/clang-tools-extra/clang-tidy/bugprone/NarrowingConversionsCheck.cpp

Lines 557 to 560 in 7500cea

	handleBinaryOperator(Context, CO->getLHS()->getExprLoc(), Lhs,
	*CO->getLHS());
	handleBinaryOperator(Context, CO->getRHS()->getExprLoc(), Lhs,
	*CO->getRHS());

[llvmbot]

@llvm/issue-subscribers-clang-tidy

Author: Andrey (AndreyG)

```c char test(int cond, char c) { char ret = cond > 0 ? ':' : c; // warning: narrowing conversion from 'int' to signed type 'char' is implementation-defined return ret; } ``` https://godbolt.org/z/6P8Yaqn4o