fixes #22122
The commit fixes a bug in Nim's effects checker where raise statements
with case/if expressions (commonly from template expansion) failed to
track exception types from individual branches.
Problem: addRaiseEffect only saw the outermost expression. When a
template like getTransportError(err) expanded to a case expression
raising 3 different exception types, the compiler only registered the
top-level call — missing the branch-level exceptions.
Fix (2 files):
- compiler/sempass2.nim: Added skipHiddenConv to strip implicit type
coercion nodes (nkHiddenStdConv/nkHiddenSubConv) that hide the control
flow structure. Added addRaiseEffectsFromExpr that recursively walks
into case/if/block/stmtlist expressions to find raise effects in each
branch body. Changed the nkRaiseStmt handler to use this new function.
- tests/effects/tcase_raises.nim: Test with templates that expand to
case expressions raising different exception types, verified via
{.raises: [].} pragma.
Reverts nim-lang/Nim#25845
```nim
case ecode
of ECONNABORTED, EPERM, ETIMEDOUT, ENOTCONN:
getConnectionAbortedError(ecode)
of EMFILE, ENFILE, ENOBUFS, ENOMEM:
getTransportTooManyError(ecode)
else:
(ref TransportOsError)(code: ecode,
msg: "(" & $int(ecode) & ") " & osErrorMsg(ecode))
```
The compiler inserts a hidden conv for the case expression. Perhaps we
can skip hidden convs to inspect the types that are actually raised
fixes#22122
The root cause is in the effect tracker: raise was recording the whole
conditional expression as one exception source, so semantic checking
only saw the widened common base type instead of the concrete exception
classes from each branch.
