It's literally true that Rust tried and failed in the sense that Rust's early design was extremely similar to Swift's, polymorphic compilation and all, and it was thrown out when it didn't seem to work. Swift pushed on it harder, and got it to work.

But it's less so true in the sense that the two teams had different use cases, and simply took divergent paths. Rust took the "easier"* path that limited expressivity in favour of a simple execution model that requires a minimal runtime, which in turn enabled them to focus on more interesting static analyses. Swift took the other path.

* This may sound like a slight against Rust, but both the Swift and Rust folks who worked on this stuff agree that what Swift did is a comically huge amount of work in pursuit of a relatively niche use case (idiomatic-feeling system apis). There's only so much time in the world, and Rust spent its time on other problems.

> But it's less so true in the sense that the two teams had different use cases, and simply took divergent paths. Rust took the "easier"* path that limited expressivity in favour of a simple execution model that requires a minimal runtime, which in turn enabled them to focus on more interesting static analyses. Swift took the other path.

> * This may sound like a slight against Rust, but both the Swift and Rust folks who worked on this stuff agree that what Swift did is a comically huge amount of work in pursuit of a relatively niche use case (idiomatic-feeling system apis). There's only so much time in the world, and Rust spent its time on other problems.

That I completely agree with and don't think is a slight at all: the work you outlined for Swift to have a stable ABI was a humongous (and truly novel and original) undertaking, but because it's so large it needs a real motivation and an expectation of ROI, and I don't think that ROI was / would have been there for Rust: there is little chance that a system would be shipped with Rust as the system and application libraries baseline (in the sense of libraries which are expected to be consumed essentially only by rust, which is what a rust ABI would imply), so while there are use cases for a Rust ABI they're limited (safer plugins and the like, maybe a system-provided dynamically linked stdlib).

On the other hand Swift is intended as the baseline applications language on all Apple platforms, meaning Apple has a large incentive to be able to ship and update swift-level libraries as part of their OS and other packages, in order both to reduce application bundle sizes and be able to update libraries as they go (without those libraries being limited to fairly shallow shims over C-level libraries where the actual meat would be).