Earlier quoted context omitted.
From the article: > Even in a release build, the compiler has not optimized out the stack. As we execute more and more operations, the stack gets deeper and deeper until it inevitably overflows.
That touches on why TCO/TCE is desirable, but it doesn't address why the Rust devs chose to use a keyword for guaranteed TCE.
See my prior comment: IMO it's the caller's issue that (guaranteed) TCE is needed. The callee should not have to do anything.
One of the things I forget to give thanks to the Rust designers for is the default of immutability. I remember my days in a Java environment where policy was "everything needs to be declared final" (so "final" got spattered all over the place) with zero nostalgia. Requiring TCE callees to explicitly represent themselves as TCE-friendly would be the same sort of abomination.