fsmonitor-settings: virtual repos are incompatible with FSMonitor

Virtual repos, such as GVFS (aka VFS for Git), are incompatible
with FSMonitor.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

compat/fsmonitor/fsm-settings-win32.c

@@ -3,7 +3,33 @@
 #include "repository.h"
 #include "fsmonitor-settings.h"
 
+/*
+ * GVFS (aka VFS for Git) is incompatible with FSMonitor.
+ *
+ * Granted, core Git does not know anything about GVFS and we
+ * shouldn't make assumptions about a downstream feature, but users
+ * can install both versions.  And this can lead to incorrect results
+ * from core Git commands.  So, without bringing in any of the GVFS
+ * code, do a simple config test for a published config setting.  (We
+ * do not look at the various *_TEST_* environment variables.)
+ */
+static enum fsmonitor_reason is_virtual(struct repository *r)
+{
+	const char *const_str;
+
+	if (!repo_config_get_value(r, "core.virtualfilesystem", &const_str))
+		return FSMONITOR_REASON_VIRTUAL;
+
+	return FSMONITOR_REASON_ZERO;
+}
+
 enum fsmonitor_reason fsm_os__incompatible(struct repository *r)
 {
+	enum fsmonitor_reason reason;
+
+	reason = is_virtual(r);
+	if (reason)
+		return reason;
+
 	return FSMONITOR_REASON_ZERO;
 }

fsmonitor-settings.c

@@ -155,6 +155,11 @@ static void create_reason_message(struct repository *r,
 			      _("bare repos are incompatible with fsmonitor"));
 		return;
 
+	case FSMONITOR_REASON_VIRTUAL:
+		strbuf_addstr(buf_reason,
+			      _("virtual repos are incompatible with fsmonitor"));
+		return;
+
 	default:
 		BUG("Unhandled case in create_reason_message '%d'", s->reason);
 	}

fsmonitor-settings.h

@@ -16,6 +16,7 @@ enum fsmonitor_mode {
 enum fsmonitor_reason {
 	FSMONITOR_REASON_ZERO = 0,
 	FSMONITOR_REASON_BARE = 1,
+	FSMONITOR_REASON_VIRTUAL = 2,
 };
 
 void fsm_settings__set_ipc(struct repository *r);

t/t7519-status-fsmonitor.sh

@@ -81,6 +81,15 @@ test_expect_success FSMONITOR_DAEMON 'run fsmonitor-daemon in bare repo' '
 	grep "bare repos are incompatible with fsmonitor" actual
 '
 
+test_expect_success MINGW,FSMONITOR_DAEMON 'run fsmonitor-daemon in virtual repo' '
+	test_when_finished "rm -rf ./fake-virtual-clone actual" &&
+	git init fake-virtual-clone &&
+	test_must_fail git -C ./fake-virtual-clone \
+			   -c core.virtualfilesystem=true \
+			   fsmonitor--daemon run 2>actual &&
+	grep "virtual repos are incompatible with fsmonitor" actual
+'
+
 test_expect_success 'setup' '
 	mkdir -p .git/hooks &&
 	: >tracked &&