Logical pathname namestring syntax incompletely supported

[Richard M Kreuter]

Given this fragment of the LPN namestring syntax BNF in 19.3.1,

logical-pathname::= [host host-marker]
                    [relative-directory-marker] {directory directory-marker}*
                    [name] [type-marker type [version-marker version]]

I believe the name portion of a logical pathname namestring ought to be optional.

However, SBCL doesn't parse LPNs lacking name portions [1].

The attached patch suffices to support this syntax in the LPN namestring parser and constructor.

Uname and features below [2].

[1) Transcript of error.

sh ./run-sbcl.sh --no-userinit --no-sysinit
This is SBCL 1.4.10.145-0ec8b87b2, an implementation of ANSI Common Lisp.
More information about SBCL is available at <http://www.sbcl.org/>.

SBCL is free software, provided as is, with absolutely no warranty.
It is mostly in the public domain; some portions are provided under
BSD-style licenses. See the CREDITS and COPYING files in the
distribution for more information.
* (logical-pathname "sys:a;.c.newest")

debugger invoked on a SIMPLE-TYPE-ERROR in thread
#<THREAD "main thread" RUNNING {10005505B3}>:
  "sys:a;.c.newest" is not a valid logical namestring:
  parse error in namestring: expecting a file name, got #\..
  sys:a;.c.newest
        ^

Type HELP for debugger help, or (SB-EXT:EXIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [ABORT] Exit debugger, returning to top level.

((FLET SB-IMPL::OOPS :IN LOGICAL-PATHNAME) #<SB-KERNEL:NAMESTRING-PARSE-ERROR {100182E443}>)

[2] uname and *FEATURES*

Darwin m5.localdomain 14.5.0 Darwin Kernel Version 14.5.0: Wed Jul 29 02:26:53 PDT 2015; root:xnu-2782.40.9~1/RELEASE_X86_64 x86_64

* *features*

(:X86-64 :64-BIT :64-BIT-REGISTERS :ALIEN-CALLBACKS :ANSI-CL :ASH-RIGHT-VOPS
 :BSD :C-STACK-IS-CONTROL-STACK :CALL-SYMBOL :COMMON-LISP
 :COMPACT-INSTANCE-HEADER :COMPARE-AND-SWAP-VOPS :COMPLEX-FLOAT-VOPS
 :CYCLE-COUNTER :DARWIN :DARWIN9-OR-BETTER :FLOAT-EQL-VOPS
 :FP-AND-PC-STANDARD-SAVE :GENCGC :IEEE-FLOATING-POINT :IMMOBILE-CODE
 :IMMOBILE-SPACE :INLINE-CONSTANTS :INODE64 :INTEGER-EQL-VOP :LINKAGE-TABLE
 :LITTLE-ENDIAN :MACH-EXCEPTION-HANDLER :MACH-O :MEMORY-BARRIER-VOPS
 :MULTIPLY-HIGH-VOPS :OS-PROVIDES-BLKSIZE-T :OS-PROVIDES-DLADDR
 :OS-PROVIDES-DLOPEN :OS-PROVIDES-PUTWC :OS-PROVIDES-SUSECONDS-T
 :PACKAGE-LOCAL-NICKNAMES :RAW-INSTANCE-INIT-VOPS :RAW-SIGNED-WORD
 :RELOCATABLE-HEAP :SB-DOC :SB-EVAL :SB-LDB :SB-PACKAGE-LOCKS :SB-SIMD-PACK
 :SB-SOURCE-LOCATIONS :SB-THREAD :SB-UNICODE :SBCL :STACK-ALLOCATABLE-CLOSURES
 :STACK-ALLOCATABLE-FIXED-OBJECTS :STACK-ALLOCATABLE-LISTS
 :STACK-ALLOCATABLE-VECTORS :STACK-GROWS-DOWNWARD-NOT-UPWARD :SYMBOL-INFO-VOPS
 :UD2-BREAKPOINTS :UNBIND-N-VOP :UNDEFINED-FUN-RESTARTS :UNIX
 :UNWIND-TO-FRAME-AND-CALL-VOP)