[Qemu-devel] [PATCH v10 23/25] qapi: Reserve 'u' member name

[Eric Blake <eblake@redhat.com>]

Now that we have separated union tag values from colliding with
non-variant C names, by naming the union 'u', we should reserve
this name for our use.  Note that we want to forbid 'u' even in
a struct with no variants, because it is possible for a future
qemu release to extend QMP in a backwards-compatible manner while
converting from a struct to a flat union.  Fortunately, no
existing clients were using this member name.  If we ever find
the need for QMP to have a member 'u', we could at that time
relax things, perhaps by having c_name() munge the QMP member to
'q_u'.

Note that we cannot forbid 'u' everywhere (by adding the
rejection code to check_name()), because the existing QKeyCode
enum already uses it.  And it is still okay to use it as a
branch name within a union, although not worth adding a
positive test to qapi-schema-test for this corner case.

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

---
v10: new patch, split from 1/17 and 3/17; by deferring this until
after the rename was complete, it reduces churn due to the new feature
---
 scripts/qapi.py                        | 2 +-
 tests/Makefile                         | 1 +
 tests/qapi-schema/struct-member-u.err  | 1 +
 tests/qapi-schema/struct-member-u.exit | 1 +
 tests/qapi-schema/struct-member-u.json | 7 +++++++
 tests/qapi-schema/struct-member-u.out  | 0
 6 files changed, 11 insertions(+), 1 deletion(-)
 create mode 100644 tests/qapi-schema/struct-member-u.err
 create mode 100644 tests/qapi-schema/struct-member-u.exit
 create mode 100644 tests/qapi-schema/struct-member-u.json
 create mode 100644 tests/qapi-schema/struct-member-u.out

diff --git a/scripts/qapi.py b/scripts/qapi.py
index 8b9f5f7..b941ccf 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -490,7 +490,7 @@ def check_type(expr_info, source, value, allow_array=False,
     for (key, arg) in value.items():
         check_name(expr_info, "Member of %s" % source, key,
                    allow_optional=allow_optional)
-        if c_name(key).startswith('has_'):
+        if key == 'u' or c_name(key).startswith('has_'):
             raise QAPIExprError(expr_info,
                                 "Member of %s uses reserved name '%s'"
                                 % (source, key))
diff --git a/tests/Makefile b/tests/Makefile
index 9194264..8c239f8 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -326,6 +326,7 @@ qapi-schema += struct-base-clash-deep.json
 qapi-schema += struct-base-clash.json
 qapi-schema += struct-data-invalid.json
 qapi-schema += struct-member-invalid.json
+qapi-schema += struct-member-u.json
 qapi-schema += struct-name-list.json
 qapi-schema += trailing-comma-list.json
 qapi-schema += trailing-comma-object.json
diff --git a/tests/qapi-schema/struct-member-u.err b/tests/qapi-schema/struct-member-u.err
new file mode 100644
index 0000000..0dc354c
--- /dev/null
+++ b/tests/qapi-schema/struct-member-u.err
@@ -0,0 +1 @@
+tests/qapi-schema/struct-member-u.json:7: Member of 'data' for struct 'Oops' uses reserved name 'u'
diff --git a/tests/qapi-schema/struct-member-u.exit b/tests/qapi-schema/struct-member-u.exit
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/tests/qapi-schema/struct-member-u.exit
@@ -0,0 +1 @@
+1
diff --git a/tests/qapi-schema/struct-member-u.json b/tests/qapi-schema/struct-member-u.json
new file mode 100644
index 0000000..1eaf0f3
--- /dev/null
+++ b/tests/qapi-schema/struct-member-u.json
@@ -0,0 +1,7 @@
+# Potential C member name collision
+# We reject use of 'u' as a member name, to allow it for internal use in
+# putting union branch members in a separate namespace from QMP members.
+# This is true even for non-unions, because it is possible to convert a
+# struct to flat union while remaining backwards compatible in QMP.
+# TODO - we could munge the member name to 'q_u' to avoid the collision
+{ 'struct': 'Oops', 'data': { 'u': 'str' } }
diff --git a/tests/qapi-schema/struct-member-u.out b/tests/qapi-schema/struct-member-u.out
new file mode 100644
index 0000000..e69de29
-- 
2.4.3