Not at all. Rust has proper sum types, that it can return just like anything else in the language, while Go has a special cased error return slot (one may be tempted to call it an ugly hack), and it can return a value on both, which it does in some standard library calls.
Not at all. Go has an error type, and Go functions have the ability to return zero, one, two, or more items, ordered however the developer likes. An error may be among those, as desired, and populated as desired.
Some software also writes to both STDOUT and STDERR.
I know, special cased may have been better worded as "just a convention". My point is, this is not much different than using a thread-local variable, like errno, and adds useless confusion - your return values represent n*m values, while there is only n+m case with proper error semantics.
Re STDERR: but shells don't decide whether a program execution failed on having written to STDERR, but by the returned singular error code.
Not at all. Rust has proper sum types, that it can return just like anything else in the language, while Go has a special cased error return slot (one may be tempted to call it an ugly hack), and it can return a value on both, which it does in some standard library calls.