[EH] Rename delegateTarget to exceptionTarget (NFC) #3562
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So far `Try`'s label is only targetted by `delegate`s, but it turns out `rethrow` also has to follow the same rule as `delegate` so it needs to target a `Try` label. So this renames variables like `delegateTargetNames` to `exceptionTargetNames` and methods like `replaceDelegateTargets` to `replaceExceptionTargets`. I considered `tryTarget`, but the branch/block counterpart name we use is not `blockTarget` but `branchTarget`, so I chose `exceptionTarget`.
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kripken
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I was previously mistaken about `rethrow`'s argument rule and thought it only counted `catch`'s depth. But it turns out it follows the same rule with `delegate`'s label: the immediate argument is comptuted in the same way as branch labels, but it only can target `try` labels (semantically it targets that `try`'s corresponding `catch`); otherwise it will be a validation failure. Unlike `delegate`, `rethrow`'s label denotes not where to rethrow, but which exception to rethrow. For example, ```wasm try $l0 catch ($l0) try $l1 catch ($l1) rethrow $l0 ;; rethrow the exception caught by 'catch ($l0)' end end ``` Refer to this comment for the more detailed informal semantics: WebAssembly/exception-handling#146 (comment) This also reverses some of `delegateTarget` -> `exceptionTarget` changes done in WebAssembly#3562 in the validator. Label validation rules apply differently for `delegate` and `rethrow` for try-catch. For example, this is valid: ```wasm try $l0 try delegate $l0 catch ($l0) end ``` But this is NOT valid: ```wasm try $l0 catch ($l0) try delegate $l0 end ``` So `try`'s label should be used within try-catch range (not catch-end range) for `delegate`s. But for the `rethrow` the rule is different. For example, this is valid: ```wasm try $l0 catch ($l0) rethrow $l0 end ``` But this is NOT valid: ```wasm try $l0 rethrow $l0 catch ($l0) end ``` So the `try`'s label should be used within catch-end range instead.
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I was previously mistaken about `rethrow`'s argument rule and thought it only counted `catch`'s depth. But it turns out it follows the same rule `delegate`'s label: the immediate argument follows the same rule as when computing branch labels, but it only can target `try` labels (semantically it targets that `try`'s corresponding `catch`); otherwise it will be a validation failure. Unlike `delegate`, `rethrow`'s label denotes not where to rethrow, but which exception to rethrow. For example, ```wasm try $l0 catch ($l0) try $l1 catch ($l1) rethrow $l0 ;; rethrow the exception caught by 'catch ($l0)' end end ``` Refer to this comment for the more detailed informal semantics: WebAssembly/exception-handling#146 (comment) --- This also reverts some of `delegateTarget` -> `exceptionTarget` changes done in #3562 in the validator. Label validation rules apply differently for `delegate` and `rethrow` for try-catch. For example, this is valid: ```wasm try $l0 try delegate $l0 catch ($l0) end ``` But this is NOT valid: ```wasm try $l0 catch ($l0) try delegate $l0 end ``` So `try`'s label should be used within try-catch range (not catch-end range) for `delegate`s. But for the `rethrow` the rule is different. For example, this is valid: ```wasm try $l0 catch ($l0) rethrow $l0 end ``` But this is NOT valid: ```wasm try $l0 rethrow $l0 catch ($l0) end ``` So the `try`'s label should be used within catch-end range instead.
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So far
Try's label is only targetted bydelegates, but it turns outrethrowalso has to follow the same rule asdelegateso it needs totarget a
Trylabel. So this renames variables likedelegateTargetNamestoexceptionTargetNamesand methods likereplaceDelegateTargetstoreplaceExceptionTargets.I considered
tryTarget, but the branch/block counterpart name we useis not
blockTargetbutbranchTarget, so I choseexceptionTarget.The patch that fixes
rethrow's target will follow; this is thepreparation for that.