[PATCH v3] qapi: give available enum values as error hint

[marcandre . lureau]

From: Marc-André Lureau <marcandre.lur...@redhat.com>

This allows for a more pleasant user experience.

Before:
$ ./qemu-system-x86_64 -display egl-headless,gl=
qemu-system-x86_64: -display egl-headless,gl=: Parameter 'gl' does not accept 
value ''

After:
$ ./qemu-system-x86_64 -display egl-headless,gl=
qemu-system-x86_64: -display egl-headless,gl=: Parameter 'gl' does not accept 
value ''
Acceptable values are 'off', 'on', 'core', 'es'

Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
---
 qapi/qapi-visit-core.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 6c13510a2b..7468b8c7b8 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -392,9 +392,25 @@ static bool output_type_enum(Visitor *v, const char *name, 
int *obj,
     return visit_type_str(v, name, &enum_str, errp);
 }
 
+static void error_append_qapi_enum_hint(Error *const *errp, const QEnumLookup 
*lookup)
+{
+    int i;
+
+    error_append_hint(errp, "Acceptable values are ");
+    for (i = 0; i < lookup->size; i++) {
+        error_append_hint(errp, "'%s'", lookup->array[i]);
+        if (i + 1 < lookup->size) {
+            error_append_hint(errp, ", ");
+        }
+    }
+    error_append_hint(errp, "\n");
+}
+
+
 static bool input_type_enum(Visitor *v, const char *name, int *obj,
                             const QEnumLookup *lookup, Error **errp)
 {
+    ERRP_GUARD();
     int64_t value;
     g_autofree char *enum_str = NULL;
 
@@ -406,6 +422,7 @@ static bool input_type_enum(Visitor *v, const char *name, 
int *obj,
     if (value < 0) {
         error_setg(errp, "Parameter '%s' does not accept value '%s'",
                    name ? name : "null", enum_str);
+        error_append_qapi_enum_hint(errp, lookup);
         return false;
     }
 
-- 
2.39.2