From a6245a56d82d50e2f3f502ca81ba332bef9ba41d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Uwe=20Kr=C3=BCger?=
 <45282134+UweKrueger@users.noreply.github.com>
Date: Sun, 25 Jul 2021 14:34:48 +0200
Subject: [PATCH] builtin: fix Windows panic message (#10952)

---
 vlib/builtin/builtin_windows.c.v | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/vlib/builtin/builtin_windows.c.v b/vlib/builtin/builtin_windows.c.v
index 741009c326..97592cff0c 100644
--- a/vlib/builtin/builtin_windows.c.v
+++ b/vlib/builtin/builtin_windows.c.v
@@ -54,8 +54,6 @@ fn C.SymFromAddr(h_process voidptr, address u64, p_displacement voidptr, p_symbo
 
 fn C.SymGetLineFromAddr64(h_process voidptr, address u64, p_displacement voidptr, p_line &Line64) int
 
-fn C.FormatMessage(dwFlags u32, lpSource voidptr, dwMessageId u32, dwLanguageId u32, lpBuffer &voidptr, nSize u32, Arguments voidptr) u32
-
 // Ref - https://docs.microsoft.com/en-us/windows/win32/api/dbghelp/nf-dbghelp-symsetoptions
 const (
 	symopt_undname               = 0x00000002
@@ -282,17 +280,19 @@ fn break_if_debugger_attached() {
 
 // return an error message generated from WinAPI's `LastError`
 pub fn winapi_lasterr_str() string {
-	mut msgbuf := &byte(0)
 	err_msg_id := C.GetLastError()
-	res := C.FormatMessage(C.FORMAT_MESSAGE_ALLOCATE_BUFFER | C.FORMAT_MESSAGE_FROM_SYSTEM,
-		C.NULL, err_msg_id, 0, &msgbuf, 0, C.NULL)
+	if err_msg_id == 8 {
+		// handle this case special since `FormatMessage()` might not work anymore
+		return 'insufficient memory'
+	}
+	mut msgbuf := &u16(0)
+	res := C.FormatMessage(C.FORMAT_MESSAGE_ALLOCATE_BUFFER | C.FORMAT_MESSAGE_FROM_SYSTEM | C.FORMAT_MESSAGE_IGNORE_INSERTS,
+		C.NULL, err_msg_id, C.MAKELANGID(C.LANG_NEUTRAL, C.SUBLANG_DEFAULT), &msgbuf,
+		0, C.NULL)
 	err_msg := if res == 0 {
-		'unknown error $err_msg_id'
+		'Win-API error $err_msg_id'
 	} else {
-		string{
-			str: msgbuf
-			len: int(res)
-		}
+		unsafe { string_from_wide(msgbuf) }
 	}
 	return err_msg
 }