patch 8.2.4338: an error from an expression mapping messes up the display
Problem: An error from an expression mapping messes up the display.
Solution: When the expression results in an empty string return K_IGNORE.
In cmdline mode redraw the command line. (closes #9726)
diff --git a/src/testdir/test_mapping.vim b/src/testdir/test_mapping.vim
index b9c9fa5..e18927c 100644
--- a/src/testdir/test_mapping.vim
+++ b/src/testdir/test_mapping.vim
@@ -549,6 +549,38 @@
call delete('XtestExprMap')
endfunc
+func Test_expr_map_error()
+ CheckScreendump
+
+ let lines =<< trim END
+ func Func()
+ throw 'test'
+ return ''
+ endfunc
+
+ nnoremap <expr> <F2> Func()
+ cnoremap <expr> <F2> Func()
+
+ call test_override('ui_delay', 10)
+ END
+ call writefile(lines, 'XtestExprMap')
+ let buf = RunVimInTerminal('-S XtestExprMap', #{rows: 10})
+ call TermWait(buf)
+ call term_sendkeys(buf, "\<F2>")
+ call TermWait(buf)
+ call term_sendkeys(buf, "\<CR>")
+ call VerifyScreenDump(buf, 'Test_map_expr_2', {})
+
+ call term_sendkeys(buf, ":abc\<F2>")
+ call VerifyScreenDump(buf, 'Test_map_expr_3', {})
+ call term_sendkeys(buf, "\<Esc>0")
+ call VerifyScreenDump(buf, 'Test_map_expr_4', {})
+
+ " clean up
+ call StopVimInTerminal(buf)
+ call delete('XtestExprMap')
+endfunc
+
" Test for mapping errors
func Test_map_error()
call assert_fails('unmap', 'E474:')