io.files: add with-cd. Related to #1214.

basis/io/directories/directories-docs.factor

@@ -12,7 +12,13 @@ HELP: cd
 { $description "Changes the current working directory of the Factor process." }
 { $notes "User code should use " { $link with-directory } " or " { $link set-current-directory } " instead." } ;
 
-{ cd cwd current-directory set-current-directory with-directory } related-words
+HELP: with-cd
+{ $values
+    { "path" "a pathname string" } { "quot" quotation }
+}
+{ $description "Changes Factor's current working directory (as far as the operating system is concerned). Then, calls the quotation and restores the original directory even if an error is thrown." } ;
+
+{ cd cwd with-cd current-directory set-current-directory with-directory } related-words
 
 HELP: current-directory
 { $description "A variable holding the current directory as an absolute path. Words that use the filesystem do so in relation to this variable."

core/io/files/files-tests.factor

@@ -1,10 +1,9 @@
 USING: alien alien.c-types alien.data arrays classes.struct
-debugger.threads destructors generic.single io io.directories
-io.encodings.8-bit.latin1 io.encodings.ascii
+compiler.units continuations destructors generic.single io
+io.directories io.encodings.8-bit.latin1 io.encodings.ascii
 io.encodings.binary io.encodings.string io.files
 io.files.private io.files.temp io.files.unique kernel make math
-sequences specialized-arrays system threads tools.test vocabs
-compiler.units ;
+sequences specialized-arrays system threads tools.test vocabs ;
 FROM: specialized-arrays.private => specialized-array-vocab ;
 SPECIALIZED-ARRAY: int
 IN: io.files.tests
@@ -271,3 +270,20 @@ CONSTANT: pt-array-1
     "closing-twice" unique-file ascii <file-writer>
     [ dispose ] [ dispose ] bi
 ] unit-test
+
+! Test with-cd
+{ t } [
+    cwd
+    "resource:core/" [ "hi" print ] with-cd
+    cwd =
+] unit-test
+
+{ t } [
+    cwd
+    [ "resource:core/" [ "nick cage" throw ] with-cd ] [ drop ] recover
+    cwd =
+] unit-test
+
+[
+    "resource:core/" [ "nick cage" throw ] with-cd
+] [ "nick cage" = ] must-fail-with

core/io/files/files.factor

@@ -1,8 +1,8 @@
 ! Copyright (C) 2004, 2009 Slava Pestov, Daniel Ehrenberg.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: alien.strings init io io.backend io.encodings
-io.encodings.utf8 io.files.private io.pathnames kernel
-kernel.private namespaces sequences splitting system ;
+USING: alien.strings continuations init io io.backend
+io.encodings io.encodings.utf8 io.files.private io.pathnames
+kernel kernel.private namespaces sequences splitting system ;
 IN: io.files
 
 SYMBOL: +retry+ ! just try the operation again without blocking
@@ -70,6 +70,11 @@ HOOK: cwd io-backend ( -- path )
 
 M: object cwd ( -- path ) "." ;
 
+: with-cd ( path quot -- )
+    [ [ absolute-path cd ] curry ] dip compose
+    cwd [ cd ] curry
+    [ ] cleanup ; inline
+
 PRIVATE>
 
 : init-resource-path ( -- )