[armedbear-cvs] r14172 - trunk/abcl/doc/design/pathnames

[mevenson at common-lisp.net]

Author: mevenson
Date: Mon Oct  8 11:07:00 2012
New Revision: 14172

Log:
Document current plans for resolution of issues involving the merging with JAR-PATHNAME defaults.

Modified:
   trunk/abcl/doc/design/pathnames/merging-defaults.markdown

Modified: trunk/abcl/doc/design/pathnames/merging-defaults.markdown
==============================================================================
--- trunk/abcl/doc/design/pathnames/merging-defaults.markdown	Mon Oct  8 11:06:59 2012	(r14171)
+++ trunk/abcl/doc/design/pathnames/merging-defaults.markdown	Mon Oct  8 11:07:00 2012	(r14172)
@@ -1,32 +1,73 @@
-# ISSUE MERGE-PATHNAMES with specialization of JAR-PATHNAME and URL-PATHNAME
+# ISSUE MERGE-PATHNAMES with specialization of JAR-PATHNAME 
 
-## UC0 Loading jna.jar for CFFI via Quicklisp
+We wish to resolve the following issues.
 
-This happens in loading systems via ASDF recursively in jars (abcl-contrib.jar)
+## UC0 Loading jna.jar for CFFI via Quicklisp
 
-## UC1
-If *DEFAULT-PATHNAME-DEFAULTS* is a JAR-PATHNAME, commands like 
+This happens in loading systems via ASDF recursively in jars, most
+importantly for those packaged in 'abcl-contrib.jar', which prevents
+CFFI from loading the necessary JNA code.
+
+## UC1.1
+If *DEFAULT-PATHNAME-DEFAULTS* is a JAR-PATHNAME, commands that would
+normally be expected to work such as 
 
-    CL-USER: (probe-file #"/") 
+    CL-USER> (probe-file #p"/") 
     
 will fail.  
 
+### UC1.2
+
+If *DEFAULT-PATHNAME-DEFAULTS* is a JAR-PATHNAME, COMPILE-FILE
+operations specifying an OUTPUT-FILE with a NIL DEVICE will fail, as
+COMPILE-FILE-PATHNAME is required to merge its arguments with the
+defaults.
 
-## Questions
+## CLHS Citations
+
+Some especially relevant portions of the CLHS for consideration.
 
 ###  19.2.3 Merging Pathnames
+http://www.lispworks.com/documentation/HyperSpec/Body/19_bc.htm
 
-Except as explicitly specified otherwise, for functions that
+"Except as explicitly specified otherwise, for functions that
 manipulate or inquire about files in the file system, the pathname
 argument to such a function is merged with *default-pathname-defaults*
-before accessing the file system (as if by merge-pathnames).
+before accessing the file system (as if by merge-pathnames)."
+
+Note that this implies that the arguments to PARSE-NAMESTRING--which
+is what the SHARSIGN-P reader macro correpsponds to--should not be
+merged.
+
+
+## 19.2.2.2.3 :UNSPECIFIC as a Component Value
+http://www.lispworks.com/documentation/HyperSpec/Body/19_bbbc.htm
+
+"If :unspecific is the value of a pathname component, the component is
+considered to be ``absent'' or to ``have no meaning'' in the filename
+being represented by the pathname."
+
+Having an :UNSPECIFIC DEVICE when a PATHNAME refers to a file would
+address problems when merging when the defaults contains a JAR-PATHNAME.
+
+### MERGE-PATHNAMES 
+http://www.lispworks.com/documentation/HyperSpec/Body/f_merge_.htm
+
+"If pathname explicitly specifies a host and not a device, and if the
+host component of default-pathname matches the host component of
+pathname, then the device is taken from the default-pathname;
+otherwise the device will be the default file device for that host. If
+pathname does not specify a host, device, directory, name, or type,
+each such component is copied from default-pathname."
 
-Q: Does this mean that the arguments to PARSE-NAMESTRING should not be
-merged? 
+This suggests that the contents HOST should be considered as an
+additional axis of type for PATHNAME, so that when PATHNAMES of
+differing types get merged, a DEVICE which has no meaning for a given
+type does not get inserted. 
 
 ## Other implementations
 
-What is the "default" host for #p"/"?
+A survey of the the "default" host for #p"/" on startup.
 
 ### SBCL
 
@@ -38,19 +79,37 @@
 
 HOST is NIL.
 
-
 ### CCL
 
 HOST is :UNSPECIFIC. 
 
-
 ### ECL
 
 HOST is NIL.
 
-### Colophon
+## Implementation
+
+### TRUENAME sets DEVICE to :UNSPECIFIC
+
+TRUENAME sets DEVICE to :UNSPECIFIC running on non-Windows when
+resolving a path to a plain file.
+
+### Use an implicit type for merging 
+
+In the case for which a merge occurs when DEFAULT-PATHNAME
+is a JAR-PATHNAME and the following conditions hold:
+
+1.  HOST and DEVICE of the PATHNAME are NIL
+
+2.  The DIRECTORY of the PATHNAME represents an absolute path. 
+
+3.  We are not on Windows.
+
+we set the DEVICE to be :UNSPECIFIC.
+
+### COLOPHON
 
 Mark <evenson at panix.com>
 Created:  01-SEP-2012
-Revised:  01-OCT-2012
+Revised:  08-OCT-2012