[PATCH] qapi: give available enum values in error string

[marcandre . lureau]

From: Marc-André Lureau <marcandre.lureau@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=help: Parameter 'gl' does
not accept value '' (available: 'off', 'on', 'core', 'es')

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 include/qapi/util.h             |  1 +
 qapi/qapi-util.c                | 15 +++++++++++++++
 qapi/qapi-visit-core.c          |  7 +++++--
 tests/unit/check-qom-proplist.c |  4 ++--
 4 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/include/qapi/util.h b/include/qapi/util.h
index 81a2b13a33..a5363e595d 100644
--- a/include/qapi/util.h
+++ b/include/qapi/util.h
@@ -23,6 +23,7 @@ typedef struct QEnumLookup {
 } QEnumLookup;
 
 const char *qapi_enum_lookup(const QEnumLookup *lookup, int val);
+char *qapi_enum_available(const QEnumLookup *lookup);
 int qapi_enum_parse(const QEnumLookup *lookup, const char *buf,
                     int def, Error **errp);
 bool qapi_bool_parse(const char *name, const char *value, bool *obj,
diff --git a/qapi/qapi-util.c b/qapi/qapi-util.c
index 63596e11c5..19ba4b695a 100644
--- a/qapi/qapi-util.c
+++ b/qapi/qapi-util.c
@@ -84,6 +84,21 @@ int qapi_enum_parse(const QEnumLookup *lookup, const char 
*buf,
     return def;
 }
 
+char *qapi_enum_available(const QEnumLookup *lookup)
+{
+    int i;
+    GString *str = g_string_new(NULL);
+
+    for (i = 0; i < lookup->size; i++) {
+        g_string_append_printf(str, "'%s'", lookup->array[i]);
+        if (i + 1 < lookup->size) {
+            g_string_append(str, ", ");
+        }
+    }
+
+    return g_string_free(str, FALSE);
+}
+
 bool qapi_bool_parse(const char *name, const char *value, bool *obj, Error 
**errp)
 {
     if (g_str_equal(value, "on") ||
diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c
index 6c13510a2b..b887cbf3fd 100644
--- a/qapi/qapi-visit-core.c
+++ b/qapi/qapi-visit-core.c
@@ -404,8 +404,11 @@ static bool input_type_enum(Visitor *v, const char *name, 
int *obj,
 
     value = qapi_enum_parse(lookup, enum_str, -1, NULL);
     if (value < 0) {
-        error_setg(errp, "Parameter '%s' does not accept value '%s'",
-                   name ? name : "null", enum_str);
+        g_autofree char *avail = NULL;
+
+        avail = qapi_enum_available(lookup);
+        error_setg(errp, "Parameter '%s' does not accept value '%s' 
(available: %s)",
+                   name ? name : "null", enum_str, avail);
         return false;
     }
 
diff --git a/tests/unit/check-qom-proplist.c b/tests/unit/check-qom-proplist.c
index 79d4a8b89d..eb0b215abb 100644
--- a/tests/unit/check-qom-proplist.c
+++ b/tests/unit/check-qom-proplist.c
@@ -488,8 +488,8 @@ static void test_dummy_badenum(void)
 
     g_assert(dobj == NULL);
     g_assert(err != NULL);
-    g_assert_cmpstr(error_get_pretty(err), ==,
-                    "Parameter 'av' does not accept value 'yeti'");
+    g_assert_nonnull(strstr(error_get_pretty(err),
+                            "Parameter 'av' does not accept value 'yeti'"));
 
     g_assert(object_resolve_path_component(parent, "dummy0")
              == NULL);
-- 
2.39.2