fixes#25851
## Summary: `--panics:on` drops `nimErr_` check after closure calls
(#25851)
### Bug
With `--exceptions:goto` and `--panics:on`, the compiler skipped the
`nimErr_` check after indirect closure calls whose result flows directly
into another call (e.g., `result.add elem(src)`). A raise inside the
closure was silently swallowed — the loop continued, and the next
`raise` hit the already-set `nimInErrorMode` flag, overflowing its
`bool` storage into `OverflowDefect`.
### Root Cause
**ast.nim** — `canRaise` checked `fn.typ.n[0].len < effectListLen` first
(false after the expansion) and then `exceptionEffects != nil` (also
false, nil), so it returned `false` — meaning "cannot raise." The C
codegen trusted this and omitted the `nimErr_` check.
### Fix
**ast.nim** — `canRaise` now treats `nil` `exceptionEffects` as "unknown
→ can raise" (`exceptionEffects == nil` as an additional true
condition). This is defense-in-depth: even if some other path expands
the list but leaves `exceptionEffects` nil (e.g., a type with `{.tags.}`
but no `{.raises.}`), the error check is still emitted.
### Test
tclosure_err_panic_goto.nim — exercises the double-trigger pattern
(`drawBool` sets the error flag → closure call must propagate it) with
`matrix: "; --panics:on"` covering both exception modes.
Each test must have a filename of the form: t*.nim
Note:Testament is only aware of tests under a directory (eg tests/foo/) and will ignore
top-level tests like tests/tbar.nim.
Specs
Each test can contain a spec in a discard """ ... """ block.
Check out the parseSpec procedure in the specs module for a full and reliable reference
action
Specifies what action this test should take.
Default: run
Options:
compile - compiles the module and fails the test if compilations fails.
run - compiles and runs the module, fails the test if compilation or
execution of test code fails.
reject - compiles the module and fails the test if compilation succeeds.
There are certain spec keys that imply run, including output and
outputsub.
Categories
Each folder under this directory represents a test category, which can be
tested by running koch tests pcat <category> (or cat to avoid parallel
testing, which is slower).
The folder dll contains simple DLL tests.
The folder realtimeGC contains a test for validating that the realtime GC
can run properly without linking against the nimrtl.dll/so.