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Re: [Qemu-devel] [PATCH v8 14/35] qapi: Swap visit_* arguments for consi


From: Marc-André Lureau
Subject: Re: [Qemu-devel] [PATCH v8 14/35] qapi: Swap visit_* arguments for consistent 'name' placement
Date: Tue, 5 Jan 2016 15:06:00 +0100

Reviewed-by: Marc-André Lureau <address@hidden>Hi

On Mon, Dec 21, 2015 at 6:08 PM, Eric Blake <address@hidden> wrote:
> JSON uses "name":value, but many of our visitor interfaces were
> called with visit_type_FOO(v, &value, name, errp).  This can be
> a bit confusing to have to mentally swap the parameter order to
> match JSON order.  It's particularly bad for visit_start_struct(),
> where the 'name' parameter is smack in the middle of the
> otherwise-related group of 'obj, kind, size' parameters! It's
> time to do a global swap of the parameter ordering, so that the
> 'name' parameter is always immediately after the Visitor argument.
>

fwiw, I do agree.

> Additional reasons in favor of the swap: name is always an input
> parameter, while &value is sometimes an output parameter (depending
> on whether the caller is using an input visitor); and it is nicer
> to list input parameters first.  Also, the existing include/qjson.h
> prefers listing 'name' first in json_prop_*(), and I have plans to
> unify that file with the qapi visitors; listing 'name' first in
> qapi will minimize churn to the (admittedly few) qjson.h clients.
>
> The next patches will then fix object.h, visitor-impl.h, and those
> clients to match.
>
> Done by first patching scripts/qapi*.py by hand to make generated
> files do what I want, then by running the following Coccinelle
> script to affect the rest of the code base:
>  $ spatch --sp-file script `git grep -l '\bvisit_' -- '**/*.[ch]'`
> I then had to apply some touchups (Coccinelle insisted on TAB
> indentation in visitor.h, and botched the signature of
> visit_type_enum() by rewriting 'const char *const strings[]' to
> the syntactically invalid 'const char*const[] strings').
>
>     // Part 1: Swap declaration order
>     @@
>     type TV, TErr, TObj, T1, T2;
>     identifier OBJ, ARG1, ARG2;
>     @@
>      void visit_start_struct
>     -(TV v, TObj OBJ, T1 ARG1, const char *name, T2 ARG2, TErr errp)
>     +(TV v, const char *name, TObj OBJ, T1 ARG1, T2 ARG2, TErr errp)
>      { ... }
>
>     @@
>     type bool, TV, T1;
>     identifier ARG1;
>     @@
>      bool visit_optional
>     -(TV v, T1 ARG1, const char *name)
>     +(TV v, const char *name, T1 ARG1)
>      { ... }
>
>     @@
>     type TV, TErr, TObj, T1;
>     identifier OBJ, ARG1;
>     @@
>      void visit_get_next_type
>     -(TV v, TObj OBJ, T1 ARG1, const char *name, TErr errp)
>     +(TV v, const char *name, TObj OBJ, T1 ARG1, TErr errp)
>      { ... }
>
>     @@
>     type TV, TErr, TObj, T1, T2;
>     identifier OBJ, ARG1, ARG2;
>     @@
>      void visit_type_enum
>     -(TV v, TObj OBJ, T1 ARG1, T2 ARG2, const char *name, TErr errp)
>     +(TV v, const char *name, TObj OBJ, T1 ARG1, T2 ARG2, TErr errp)
>      { ... }
>
>     @@
>     type TV, TErr, TObj;
>     identifier OBJ;
>     identifier VISIT_TYPE =~ "^visit_type_";
>     @@
>      void VISIT_TYPE
>     -(TV v, TObj OBJ, const char *name, TErr errp)
>     +(TV v, const char *name, TObj OBJ, TErr errp)
>      { ... }
>
>     // Part 2: swap caller order
>     @@
>     expression V, NAME, OBJ, ARG1, ARG2, ERR;
>     identifier VISIT_TYPE =~ "^visit_type_";
>     @@
>     (
>     -visit_start_struct(V, OBJ, ARG1, NAME, ARG2, ERR)
>     +visit_start_struct(V, NAME, OBJ, ARG1, ARG2, ERR)
>     |
>     -visit_optional(V, ARG1, NAME)
>     +visit_optional(V, NAME, ARG1)
>     |
>     -visit_get_next_type(V, OBJ, ARG1, NAME, ERR)
>     +visit_get_next_type(V, NAME, OBJ, ARG1, ERR)
>     |
>     -visit_type_enum(V, OBJ, ARG1, ARG2, NAME, ERR)
>     +visit_type_enum(V, NAME, OBJ, ARG1, ARG2, ERR)
>     |
>     -VISIT_TYPE(V, OBJ, NAME, ERR)
>     +VISIT_TYPE(V, NAME, OBJ, ERR)
>     )
>
> Signed-off-by: Eric Blake <address@hidden>

The result looks good and passes the tests
Reviewed-by: Marc-André Lureau <address@hidden>

However, docs/qapi-code-gen.txt should be updated in a follow-up patch.

-- 
Marc-André Lureau



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