win32: add env var to control error dialogs

If the environment variable BB_CRITICAL_ERROR_DIALOGS is set to
1 critical error dialogs are enabled.  If unset or set to any
other value they aren't.  In either case the error messages
introduced by commit 790e37727 (win32: revert 'don't set error
mode') are issued.

The shell exports BB_CRITICAL_ERROR_DIALOGS to the environment
immediately on any change so the setting takes effect at once.

Adds 104-160 bytes.

(GitHub issue #423)

6 files changed, 12 insertions, 2 deletions

diff --git a/include/libbb.h b/include/libbb.h
index d37d4e64c..9055ed066 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -2418,6 +2418,7 @@ extern const char bbvar[] ALIGN1;
 #define BB_SKIP_ANSI_EMULATION bbafter(BB_OVERRIDE_APPLETS)
 #define BB_TERMINAL_MODE bbafter(BB_SKIP_ANSI_EMULATION)
 #define BB_SYSTEMROOT bbafter(BB_TERMINAL_MODE)
+#define BB_CRITICAL_ERROR_DIALOGS bbafter(BB_SYSTEMROOT)
 #endif
 
 extern const int const_int_0;
diff --git a/include/mingw.h b/include/mingw.h
index fae732332..93fad0605 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -639,3 +639,4 @@ char *quote_arg(const char *arg);
 char *find_first_executable(const char *name);
 char *xappendword(const char *str, const char *word);
 int windows_env(void);
+void change_critical_error_dialogs(const char *newval) FAST_FUNC;
diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index c90285ae9..121959376 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -1352,7 +1352,7 @@ int main(int argc UNUSED_PARAM, char **argv)
 
         /* Have this process handle critical errors itself:  the default
          * system-generated error dialogs may be inconvenient. */
-        SetErrorMode(SEM_FAILCRITICALERRORS);
+        change_critical_error_dialogs(getenv(BB_CRITICAL_ERROR_DIALOGS) ?: "");
 #endif
 
 #if defined(__MINGW64_VERSION_MAJOR)
diff --git a/libbb/messages.c b/libbb/messages.c
index 12079a2e0..27ba244d6 100644
--- a/libbb/messages.c
+++ b/libbb/messages.c
@@ -47,7 +47,8 @@ const char bbvar[] ALIGN1 =
                 "BB_OVERRIDE_APPLETS\0" \
                 "BB_SKIP_ANSI_EMULATION\0" \
                 "BB_TERMINAL_MODE\0" \
-                "BB_SYSTEMROOT\0";
+                "BB_SYSTEMROOT\0" \
+                "BB_CRITICAL_ERROR_DIALOGS\0";
 #endif
 const char bb_default_login_shell[] ALIGN1 = LIBBB_DEFAULT_LOGIN_SHELL;
 /* util-linux manpage says /sbin:/bin:/usr/sbin:/usr/bin,
diff --git a/shell/ash.c b/shell/ash.c
index ad77689e7..817b5635f 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -2443,6 +2443,7 @@ static const struct {
         { VSTRFIXED|VTEXTFIXED|VUNSET, BB_SKIP_ANSI_EMULATION, change_terminal_mode },
         { VSTRFIXED|VTEXTFIXED|VUNSET, BB_TERMINAL_MODE, change_terminal_mode },
         { VSTRFIXED|VTEXTFIXED|VUNSET, BB_OVERRIDE_APPLETS, change_override_applets },
+        { VSTRFIXED|VTEXTFIXED|VUNSET, BB_CRITICAL_ERROR_DIALOGS, change_critical_error_dialogs },
 #endif
 };
 
diff --git a/win32/mingw.c b/win32/mingw.c
index 4398f5462..49e1bcfa4 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -2507,3 +2507,9 @@ windows_env(void)
         }
         return FALSE;
 }
+
+void FAST_FUNC
+change_critical_error_dialogs(const char *newval)
+{
+        SetErrorMode(strcmp(newval, "1") == 0 ? 0 : SEM_FAILCRITICALERRORS);
+}