vim-patch:9.1.0999: Vim9: leaking finished exception (#31939)

Problem:  leaking finished exception
          (after v9.1.0984)
Solution: use finish_exception to clean up caught exceptions
          (Yee Cheng Chin)

In Vimscript, v:exception/throwpoint/stacktrace are supposed to reflect
the currently caught exception, and be popped after the exception is
finished (via endtry, finally, or a thrown exception inside catch).
Vim9script does not handle this properly, and leaks them instead. This
is clearly visible when launching GVim with menu enabled.  A caught
exception inside the s:BMShow() in menu.vim would show up when querying
`v:stacktrace` even though the exception was already caught and handled.

To fix this, just use the same functionality as Vimscript by calling
`finish_exception` to properly restore the states. Note that this
assumes `current_exception` is always the same as `caught_stack` which
believe should be the case.

Added tests for this. Also fix up test_stacktrace to properly test the
stack restore behavior where we have nested exceptions in catch blocks
and to also test the vim9script functionality properly.

- Also, remove its dependency on explicitly checking a line number in
  runtest.vim which is a very fragile way to write tests as any minor
  change in runtest.vim (shared among all tests) would require changing
  test_stacktrace.vim. We don't actually need such granularity in the
  test.

closes: vim/vim#16413

2051af1642

Co-authored-by: Yee Cheng Chin <ychin.git@gmail.com>

test/old/testdir/test_stacktrace.vim

@@ -10,7 +10,7 @@ func Filepath(name)
 endfunc
 
 func AssertStacktrace(expect, actual)
-  call assert_equal(#{lnum: 581, filepath: Filepath('runtest.vim')}, a:actual[0])
+  call assert_equal(Filepath('runtest.vim'), a:actual[0]['filepath'])
   call assert_equal(a:expect, a:actual[-len(a:expect):])
 endfunc
 
@@ -97,6 +97,12 @@ func Test_vstacktrace()
     call Xfunc1()
   catch
     let stacktrace = v:stacktrace
+    try
+      call Xfunc1()
+    catch
+      let stacktrace_inner = v:stacktrace
+    endtry
+    let stacktrace_after = v:stacktrace " should be restored by the exception stack to the previous one
   endtry
   call assert_equal([], v:stacktrace)
   call AssertStacktrace([
@@ -104,9 +110,15 @@ func Test_vstacktrace()
        \ #{funcref: funcref('Xfunc1'), lnum: 5, filepath: Filepath('Xscript1')},
        \ #{funcref: funcref('Xfunc2'), lnum: 4, filepath: Filepath('Xscript2')},
        \ ], stacktrace)
+  call AssertStacktrace([
+       \ #{funcref: funcref('Test_vstacktrace'), lnum: 101, filepath: s:thisfile},
+       \ #{funcref: funcref('Xfunc1'), lnum: 5, filepath: Filepath('Xscript1')},
+       \ #{funcref: funcref('Xfunc2'), lnum: 4, filepath: Filepath('Xscript2')},
+       \ ], stacktrace_inner)
+  call assert_equal(stacktrace, stacktrace_after)
 endfunc
 
-func Test_zzz_stacktrace_vim9()
+func Test_stacktrace_vim9()
   let lines =<< trim [SCRIPT]
   var stacktrace = getstacktrace()
   assert_notequal([], stacktrace)
@@ -122,11 +134,9 @@ func Test_zzz_stacktrace_vim9()
       assert_true(has_key(d, 'lnum'))
     endfor
   endtry
+  call assert_equal([], v:stacktrace)
   [SCRIPT]
   call CheckDefSuccess(lines)
-  " FIXME: v:stacktrace is not cleared after the exception handling, and this
-  " test has to be run as the last one because of this.
-  " call assert_equal([], v:stacktrace)
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab