I haven't programmed in plain C (as opposed to C++) in decades, but I can't believe it is allowed...
... but gcc on godblot only raises a warning but still happily compiles it. o_O
> Several operators convert operand values from one type to another automatically. This subclause specifies the result required from such an implicit conversion, as well as those that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes the conversions performed by most ordinary operators; it is supplemented as required by the discussion of each operator in 6.5.
Weather a conversion is allowed in a certain context should be specified for wording for that given context.
> If the expression has a type different from the return type of the function in which it appears, the value is converted as if by assignment to an object having the return type of the function.
(emphasis mine)
However I can't make sense of the footnote:
> The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not apply to the case of function return. The representation of floating-point values may have wider range or precision than implied by the type; a cast may be used to remove this extra range and precision.
Why doesn't the overlap restriction apply, if return is "as if by assignment"? Makes no sense to me.
edit: hmm, maybe not:
https://cigix.me/c17#6.3.2.3.p5
Looks like gcc rejects the implicit conversion with -std=c17 -pedantic-errors as it's such a bad idea to allow this, but ISO C actually allows this.