Issue #16726 reported an internal compiler error (`semcall.nim(229, 18)
nArg != nil`) when calling `toJs` with invalid arguments. The bug has
been fixed in the current codebase but lacked a regression test.
```nim
import std/jsffi
let a = toJs(3)
let b = a.toJs(int) # Now produces: Error: type mismatch
# Previously: internal error
```
**Changes:**
- Added `tests/js/t16726.nim` to verify proper type mismatch error is
reported instead of internal compiler error
<!-- START COPILOT ORIGINAL PROMPT -->
<details>
<summary>Original prompt</summary>
>
> ----
>
> *This section details on the original issue you should resolve*
>
> <issue_title>internal error: semcall.nim(229, 18) nArg !=
nil</issue_title>
> <issue_description>### Example
> the code below should give a clean CT error, not an internal error
> ```nim
> import std/jsffi
> let a = toJs(3)
> let b = a.toJs(int)
> ```
>
> ### Current Output
> nim r -b:js main
> compiler/semcall.nim(229, 18) `nArg != nil`
>
> ### Expected Output
> proper CT error
>
> ### Additional Information
> 1.5.1 41965880ce
> </issue_description>
>
> <agent_instructions>adds a test case for it and verify it by `./koch
temp js -r test.nim` before committing</agent_instructions>
>
> ## Comments on the Issue (you are @copilot in this section)
>
> <comments>
> <comment_new><author>@ringabout</author><body>
> related:
https://github.com/nim-lang/Nim/issues/15607</body></comment_new>
> </comments>
>
</details>
<!-- START COPILOT CODING AGENT SUFFIX -->
- Fixes nim-lang/Nim#16726
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This directory contains the test cases.
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.