[Qemu-devel] [PATCH 09/19] qapi: Remove null from schema language

Markus Armbruster posted 19 patches 6 years, 1 month ago
Maintainers: Markus Armbruster <armbru@redhat.com>, Michael Roth <mdroth@linux.vnet.ibm.com>
[Qemu-devel] [PATCH 09/19] qapi: Remove null from schema language
Posted by Markus Armbruster 6 years, 1 month ago
We represent the parse tree as OrderedDict.  We fetch optional dict
members with .get().  So far, so good.

We represent null literals as None.  .get() returns None both for
"absent" and for "present, value is the null literal".  Uh-oh.

Test features-if-invalid exposes this bug: "'if': null" is
misinterpreted as absent "if".

We added null to the schema language to "allow [...] an explicit
default value" (commit e53188ada5 "qapi: Allow true, false and null in
schema json", v2.4.0).  Hasn't happened; null is still unused except
as generic invalid value in tests/.

To fix, we'd have to replace .get() by something more careful, or
represent null differently.  Feasible, but we got more and bigger fish
to fry right now.  Remove the null literal from the schema language.
Replace null in tests by another invalid value.

Test features-if-invalid now behaves as it should.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 docs/devel/qapi-code-gen.txt                       |  4 ++--
 scripts/qapi/common.py                             |  4 ----
 tests/qapi-schema/features-if-invalid.err          |  1 +
 tests/qapi-schema/features-if-invalid.exit         |  2 +-
 tests/qapi-schema/features-if-invalid.json         |  3 +--
 tests/qapi-schema/features-if-invalid.out          | 14 --------------
 .../pragma-name-case-whitelist-crap.json           |  2 +-
 7 files changed, 6 insertions(+), 24 deletions(-)

diff --git a/docs/devel/qapi-code-gen.txt b/docs/devel/qapi-code-gen.txt
index 94f3054898..b4df31813d 100644
--- a/docs/devel/qapi-code-gen.txt
+++ b/docs/devel/qapi-code-gen.txt
@@ -52,7 +52,7 @@ Differences:
 * Strings are restricted to printable ASCII, and escape sequences to
   just '\\'.
 
-* Numbers are not supported.
+* Numbers and null are not supported.
 
 A second layer of syntax defines the sequences of JSON texts that are
 a correctly structured QAPI schema.  We provide a grammar for this
@@ -67,7 +67,7 @@ syntax in an EBNF-like notation:
   expression A separated by ,
 * Grouping: expression ( A ) matches expression A
 * JSON's structural characters are terminals: { } [ ] : ,
-* JSON's literal names are terminals: false true null
+* JSON's literal names are terminals: false true
 * String literals enclosed in 'single quotes' are terminal, and match
   this JSON string, with a leading '*' stripped off
 * When JSON object member's name starts with '*', the member is
diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
index b3383b17ef..ef7c7be4fd 100644
--- a/scripts/qapi/common.py
+++ b/scripts/qapi/common.py
@@ -548,10 +548,6 @@ class QAPISchemaParser(object):
                 self.val = False
                 self.cursor += 4
                 return
-            elif self.src.startswith('null', self.pos):
-                self.val = None
-                self.cursor += 3
-                return
             elif self.tok == '\n':
                 if self.cursor == len(self.src):
                     self.tok = None
diff --git a/tests/qapi-schema/features-if-invalid.err b/tests/qapi-schema/features-if-invalid.err
index e69de29bb2..295800b4fc 100644
--- a/tests/qapi-schema/features-if-invalid.err
+++ b/tests/qapi-schema/features-if-invalid.err
@@ -0,0 +1 @@
+tests/qapi-schema/features-if-invalid.json:2: 'if' condition must be a string or a list of strings
diff --git a/tests/qapi-schema/features-if-invalid.exit b/tests/qapi-schema/features-if-invalid.exit
index 573541ac97..d00491fd7e 100644
--- a/tests/qapi-schema/features-if-invalid.exit
+++ b/tests/qapi-schema/features-if-invalid.exit
@@ -1 +1 @@
-0
+1
diff --git a/tests/qapi-schema/features-if-invalid.json b/tests/qapi-schema/features-if-invalid.json
index e6a524196d..89c2a6c234 100644
--- a/tests/qapi-schema/features-if-invalid.json
+++ b/tests/qapi-schema/features-if-invalid.json
@@ -1,5 +1,4 @@
 # Cover feature with invalid 'if'
-# FIXME not rejected, misinterpreded as unconditional
 { 'struct': 'Stru',
   'data': {},
-  'features': [{'name': 'f', 'if': null }] }
+  'features': [{'name': 'f', 'if': false }] }
diff --git a/tests/qapi-schema/features-if-invalid.out b/tests/qapi-schema/features-if-invalid.out
index 9c2637baa3..e69de29bb2 100644
--- a/tests/qapi-schema/features-if-invalid.out
+++ b/tests/qapi-schema/features-if-invalid.out
@@ -1,14 +0,0 @@
-module None
-object q_empty
-enum QType
-    prefix QTYPE
-    member none
-    member qnull
-    member qnum
-    member qstring
-    member qdict
-    member qlist
-    member qbool
-module features-if-invalid.json
-object Stru
-    feature f
diff --git a/tests/qapi-schema/pragma-name-case-whitelist-crap.json b/tests/qapi-schema/pragma-name-case-whitelist-crap.json
index 58382bf4e4..734e1c617b 100644
--- a/tests/qapi-schema/pragma-name-case-whitelist-crap.json
+++ b/tests/qapi-schema/pragma-name-case-whitelist-crap.json
@@ -1,3 +1,3 @@
 # 'name-case-whitelist' must be list of strings
 
-{ 'pragma': { 'name-case-whitelist': null } }
+{ 'pragma': { 'name-case-whitelist': false } }
-- 
2.21.0


Re: [Qemu-devel] [PATCH 09/19] qapi: Remove null from schema language
Posted by Eric Blake 6 years, 1 month ago
On 9/14/19 10:34 AM, Markus Armbruster wrote:
> We represent the parse tree as OrderedDict.  We fetch optional dict
> members with .get().  So far, so good.
> 
> We represent null literals as None.  .get() returns None both for
> "absent" and for "present, value is the null literal".  Uh-oh.
> 
> Test features-if-invalid exposes this bug: "'if': null" is
> misinterpreted as absent "if".
> 
> We added null to the schema language to "allow [...] an explicit
> default value" (commit e53188ada5 "qapi: Allow true, false and null in
> schema json", v2.4.0).  Hasn't happened; null is still unused except
> as generic invalid value in tests/.

Might happen as a way to default a '*value':'str', but we can deal with
that at the point where someone actually justifies a need for a way to
express a default like that.

> 
> To fix, we'd have to replace .get() by something more careful, or
> represent null differently.  Feasible, but we got more and bigger fish
> to fry right now.  Remove the null literal from the schema language.

Fair enough.

> Replace null in tests by another invalid value.
> 
> Test features-if-invalid now behaves as it should.
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---

> +++ b/tests/qapi-schema/features-if-invalid.json
> @@ -1,5 +1,4 @@
>  # Cover feature with invalid 'if'
> -# FIXME not rejected, misinterpreded as unconditional

Obvious conflict resolution with the typo fix earlier in the series.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org