Allow try without catch
#4600
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Allow try without catch
#4600
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when there is only a default (catch-all) that would rethrow anyway
ggreif
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Jul 8, 2024
it is not helpful: - longer - we may have several `catch`-es in the future - inconsistent with IR (which is still a `list`) - no advantages
ggreif
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Jul 9, 2024
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Jul 25, 2024
Introduces an optional `finally` clause to `try` expressions that can be used for disciplined (structured) resource management. The clause comprises a unit-valued expression (or block) that may not perform sends (or similar). It gets executed for all control paths that leave the `try`-expression, i.e. `return`, `break`, etc. code paths. For nested `try` expressions the cleanups are performed in innermost to outermost order. For last-resort cleanups (i.e. code paths trapping after an `await`) the replica invokes the callback registered as `ic0.call_on_cleanup`, and this will result in the execution of (exclusively) the `finally` blocks in (dynamic) scope. This is a new mechanism in Motoko, which was not possible to achieve earlier, and puts certain resource deallocations (e.g. of acquired locks) under the programmer's control. ----------------- TODO: - [ ] [invoke cleanup from the interpreter](https://github.com/dfinity/motoko/pull/4507/files/51bb8a1933bbf2c509447032f1ba26b8f91fa4e0#r1658678631) - [ ] make `catch` optional (non-trapping when missing) — #4600 - well, this was not really needed as pattern-match failure would just re-`throw`, so we were fine. Optimised, though. - [x] remaining FIXMEs (`arrange.ml`, etc.) - [x] `Triv` in `try` (respect edges) - [x] fix fallout - [x] forbid control-flow edges out of `finally` blocks - [x] remove all aliasing from IR - [ ] use `meta` (would `assert` currently, thus causing minor code duplication) — could be follow-up PR - [x] handle `Throw` and regular continuations in `await.ml` (instead of desugaring) - [x] adjust (AST, IR)-interpreter - ❗️this is necessary when there is no `catch`, as the exception will escape - how are label continuations invoked in the backend? (I need to know for the _last-resort callback_) - have a new `context` key sort `Cleanup`, stack up continuations of finally blocks only - extend the `kr` in `await.ml` to `krc` (`CPSAwait`), pass `Cleanup` continuations as `c` - add new primitive to compiler to set the last-resort field (not needed) - in `async.ml` lower `CPSAwait` to that too - [x] adapt `check_ir.ml`, etc. - [x] tests with `await*` - [x] fix up the syntax part - `do` ... `finally` (when there is no `catch` clause necessary) - ~means: `TryE` needs `cases list option`~ - type checking for the `finally` clause - [x] unit result - [x] trivial effect (actually Claudio made this capability-based) - [ ] that the `try` block has `await` effect — nope! - [x] other type than unit for `try` - `OtherPrim "call_raw"` + tests — nope! - `cps_asyncE` similarly to `CallPrim/3` — nope! - highlighting of `finally` - [x] for `emacs` - [x] for VSCode → dfinity/vscode-motoko#288 - [x] GitHub highlighter - [x] Changelog (breaking change, new keyword) - [x] Docs - [ ] adapt best practices: https://internetcomputer.org/docs/current/developer-docs/security/security-best-practices/inter-canister-calls#recommendation - [ ] adapt Motoko examples where locking happens
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UPDATE: I reverted a lot of it, see commit 1a7b61d for an explanation.
see #4507
TODO:
catch_optconsistentlyawait.mldidn't need changes? — see belowIn the IR when none of the
catchalternatives match, then an artificially addedre-throws the
Error. So df9389c shortcuts the creation of a silly do-nothing failure continuation when the list of alternatives is empty. It would just re-throw unconditionally anyway!Optimisation opportunity: only emit this when all of the patterns are refutable! — Done: 2329069