qapi: Tighten the regex on valid names

We already documented that qapi names should match specific
patterns (such as starting with a letter unless it was an enum
value or a downstream extension).  Tighten that from a suggestion
into a hard requirement, which frees up names beginning with a
single underscore for qapi internal usage.

The tighter regex doesn't forbid everything insane that a user
could provide (for example, a user could name a type 'Foo-lookup'
to collide with the generated 'Foo_lookup[]' for an enum 'Foo'),
but does a good job at protecting the most obvious uses, and
also happens to reserve single leading underscore for later use.

The handling of enum values starting with a digit is tricky:
commit 9fb081e introduced a subtle bug by using c_name() on
a munged value, which would allow an enum to include the
member 'q-int' in spite of our reservation.  Furthermore,
munging with a leading '_' would fail our tighter regex.  So
fix it by only munging for leading digits (which are never
ticklish in c_name()) and by using a different prefix (I
picked 'D', although any letter should do).

Add new tests, reserved-member-underscore and reserved-enum-q,
to demonstrate the tighter checking.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1447836791-369-22-git-send-email-eblake@redhat.com>
Message-Id: <1447883135-18020-1-git-send-email-eblake@redhat.com>
[Eric's fixup squashed in]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

docs/qapi-code-gen.txt

@@ -118,17 +118,17 @@ tracking optional fields.
 
 Any name (command, event, type, field, or enum value) beginning with
 "x-" is marked experimental, and may be withdrawn or changed
-incompatibly in a future release.  Downstream vendors may add
-extensions; such extensions should begin with a prefix matching
-"__RFQDN_" (for the reverse-fully-qualified-domain-name of the
-vendor), even if the rest of the name uses dash (example:
-__com.redhat_drive-mirror).  Other than downstream extensions (with
-leading underscore and the use of dots), all names should begin with a
-letter, and contain only ASCII letters, digits, dash, and underscore.
-Names beginning with 'q_' are reserved for the generator: QMP names
-that resemble C keywords or other problematic strings will be munged
-in C to use this prefix.  For example, a field named "default" in
-qapi becomes "q_default" in the generated C code.
+incompatibly in a future release.  All names must begin with a letter,
+and contain only ASCII letters, digits, dash, and underscore.  There
+are two exceptions: enum values may start with a digit, and any
+extensions added by downstream vendors should start with a prefix
+matching "__RFQDN_" (for the reverse-fully-qualified-domain-name of
+the vendor), even if the rest of the name uses dash (example:
+__com.redhat_drive-mirror).  Names beginning with 'q_' are reserved
+for the generator: QMP names that resemble C keywords or other
+problematic strings will be munged in C to use this prefix.  For
+example, a field named "default" in qapi becomes "q_default" in the
+generated C code.
 
 In the rest of this document, usage lines are given for each
 expression type, with literal strings written in lower case and

scripts/qapi.py

@@ -353,9 +353,11 @@ def discriminator_find_enum_define(expr):
     return find_enum(discriminator_type)
 
 
-# FIXME should enforce "other than downstream extensions [...], all
-# names should begin with a letter".
-valid_name = re.compile('^[a-zA-Z_][a-zA-Z0-9_.-]*$')
+# Names must be letters, numbers, -, and _.  They must start with letter,
+# except for downstream extensions which must start with __RFQDN_.
+# Dots are only valid in the downstream extension prefix.
+valid_name = re.compile('^(__[a-zA-Z0-9.-]+_)?'
+                        '[a-zA-Z][a-zA-Z0-9_-]*$')
 
 
 def check_name(expr_info, source, name, allow_optional=False,
@@ -374,8 +376,8 @@ def check_name(expr_info, source, name, allow_optional=False,
                                 % (source, name))
     # Enum members can start with a digit, because the generated C
     # code always prefixes it with the enum name
-    if enum_member:
-        membername = '_' + membername
+    if enum_member and membername[0].isdigit():
+        membername = 'D' + membername
     # Reserve the entire 'q_' namespace for c_name()
     if not valid_name.match(membername) or \
        c_name(membername, False).startswith('q_'):

tests/Makefile

@@ -318,9 +318,11 @@ qapi-schema += redefined-command.json
 qapi-schema += redefined-event.json
 qapi-schema += redefined-type.json
 qapi-schema += reserved-command-q.json
+qapi-schema += reserved-enum-q.json
 qapi-schema += reserved-member-has.json
 qapi-schema += reserved-member-q.json
 qapi-schema += reserved-member-u.json
+qapi-schema += reserved-member-underscore.json
 qapi-schema += reserved-type-kind.json
 qapi-schema += reserved-type-list.json
 qapi-schema += returns-alternate.json

tests/qapi-schema/reserved-enum-q.err

@@ -0,0 +1 @@
+tests/qapi-schema/reserved-enum-q.json:4: Member of enum 'Foo' uses invalid name 'q-Unix'

tests/qapi-schema/reserved-enum-q.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/reserved-enum-q.json

@@ -0,0 +1,4 @@
+# C entity name collision
+# We reject names like 'q-unix', because they can collide with the mangled
+# name for 'unix' in generated C.
+{ 'enum': 'Foo', 'data': [ 'unix', 'q-Unix' ] }

tests/qapi-schema/reserved-member-underscore.err

@@ -0,0 +1 @@
+tests/qapi-schema/reserved-member-underscore.json:4: Member of 'data' for struct 'Oops' uses invalid name '_oops'

tests/qapi-schema/reserved-member-underscore.exit

@@ -0,0 +1 @@
+1

tests/qapi-schema/reserved-member-underscore.json

@@ -0,0 +1,4 @@
+# C member name collision
+# We reject use of a single leading underscore in all names (names must
+# begin with a letter or a downstream extension double-underscore prefix).
+{ 'struct': 'Oops', 'data': { '_oops': 'str' } }