qapi: improve reporting of unknown or missing keys

Report the set of missing or unknown keys. And give a hint about the
accepted keys.

The error message for multiple meta type members (visible in
tests/qapi-schema/double-type.err) is not improved.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20181213123724.4866-6-marcandre.lureau@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/common.py

@@ -874,14 +874,21 @@ def check_struct(expr, info):
 
 
 def check_known_keys(info, source, keys, required, optional):
-    for key in keys:
-        if key not in required and key not in optional:
-            raise QAPISemError(info, "Unknown key '%s' in %s" % (key, source))
 
-    for key in required:
-        if key not in keys:
-            raise QAPISemError(info, "Key '%s' is missing from %s"
-                               % (key, source))
+    def pprint(elems):
+        return ', '.join("'" + e + "'" for e in sorted(elems))
+
+    missing = set(required) - set(keys)
+    if missing:
+        raise QAPISemError(info, "Key%s %s %s missing from %s"
+                           % ('s' if len(missing) > 1 else '', pprint(missing),
+                              'are' if len(missing) > 1 else 'is', source))
+    allowed = set(required + optional)
+    unknown = set(keys) - allowed
+    if unknown:
+        raise QAPISemError(info, "Unknown key%s %s in %s\nValid keys are %s."
+                           % ('s' if len(unknown) > 1 else '', pprint(unknown),
+                              source, pprint(allowed)))
 
 
 def check_keys(expr_elem, meta, required, optional=[]):

tests/qapi-schema/alternate-base.err

@@ -1 +1,2 @@
 tests/qapi-schema/alternate-base.json:4: Unknown key 'base' in alternate 'Alt'
+Valid keys are 'alternate', 'data', 'if'.

tests/qapi-schema/double-type.err

@@ -1 +1,2 @@
 tests/qapi-schema/double-type.json:2: Unknown key 'command' in struct 'bar'
+Valid keys are 'base', 'data', 'if', 'struct'.

tests/qapi-schema/unknown-expr-key.err

@@ -1 +1,2 @@
-tests/qapi-schema/unknown-expr-key.json:2: Unknown key 'bogus' in struct 'bar'
+tests/qapi-schema/unknown-expr-key.json:2: Unknown keys 'bogus', 'phony' in struct 'bar'
+Valid keys are 'base', 'data', 'if', 'struct'.

tests/qapi-schema/unknown-expr-key.json

@@ -1,2 +1,2 @@
 # we reject an expression with unknown top-level keys
-{ 'struct': 'bar', 'data': { 'string': 'str'}, 'bogus': { } }
+{ 'struct': 'bar', 'data': { 'string': 'str'}, 'bogus': { }, 'phony': { } }