fixes#10440, fixes#13871, fixes#14665, fixes#19672, fixes#23677
The false positive in #23677 was caused by behavior in
`implicitlyDiscardable` where only the last node of `if`/`case`/`try`
etc expressions were considered, as in the final node of the final
branch (in this case `else`). To fix this we use the same iteration in
`implicitlyDiscardable` that we use in `endsInNoReturn`, with the
difference that for an `if`/`case`/`try` statement to be implicitly
discardable, all of its branches must be implicitly discardable.
`noreturn` calls are also considered implicitly discardable for this
reason, otherwise stuff like `if true: discardableCall() else: error()`
doesn't compile.
However `endsInNoReturn` also had bugs, one where `finally` was
considered in noreturn checking when it shouldn't, another where only
`nkIfStmt` was checked and not `nkIfExpr`, and the node given for the
error message was bad. So `endsInNoReturn` now skips over
`skipForDiscardable` which no longer contains
`nkIfStmt`/`nkCaseStmt`/`nkTryStmt`, stores the first encountered
returning node in a var parameter for the error message, and handles
`finally` and `nkIfExpr`.
Fixing #23677 already broke a line in `syncio` so some package code
might be affected.
New issue: since `Table[A, B]` allocates its backing storage with
`newSeq[KeyValuePair[A, B]]`, it's no longer legal to create a table
with `not nil` types used as either keys or values.
* Revert "Properly wrap discarded statements (#10322)"
This reverts commit 15584879b9.
* add test for implicit discard after defer
* enable t10241 again
* make C++ tests green again
