Just a naming thing: I find myself thinking about what @John_McCall said about naming conventions, and my own vague intuition about there being an lvalue/rvalue-like distinction here that naming should respect.
Looking at the code examples in context in this proposal, my gut feeling is that the keyword should be a gerund (consuming / borrowing) in declarations:
func write(_ data: [UInt8], to file: borrowing FileDescriptor) {
^^^^^^^^^
func close(file: consuming FileDescriptor) {
^^^^^^^^^
That reads better to my eye. John was skeptical of the gerund, but darn it, in context that just flows off the mental tongue, as it were. The write function writes to a file by borrowing a FileDescriptor. It’s right there in the code.
I do also see the case for a past participle:
func write(_ data: [UInt8], to file: borrowed FileDescriptor) {
^^^^^^^^
The colon usually reads as “which is a”, and this naming fits: “Write data, which is a UInt8 array, to file, which is a borrowed FileDescriptor.” Both those options read better to me than the imperative verb borrow.
To be clear, the keyword should still be an imperative verb (consume / borrow) when applied to an expression that supplies a value:
munge(borrow thinger)
^^^^^^
funge(consume thinger)
^^^^^^^
Trying to articulate my intuition here: one describes what will happen elsewhere whenever the thing is used; the other describes what does happen right there in the usage site. That's post hoc explanation, to be clear; I'm just reacting to the fluency of the code itself.