[io grant] Improve &chdir, &indir, and IO::Path.chdir

- Deprecate `:$test` param
- Use :r, :w, :d, :x named args for tests
- Use :d test as default instead of :d + :r
- Make &chdir and &indir propagate Failure, instead of throwing
- Fix incorrect dir used in &indir if a relative IO::Path is given
    after a change to $*CWD, since IO::Path.Str does not use its $!CWD
- Fix (or reduce?) race condition in `indir` for relative paths:
    - old version took Str() $path and used $*CWD in its body to
        chdir to that $path, creating a race condition where the
        changed $*CWD made $path be relative to the wrong thing
    - new version takes IO(), so no race if an IO::Path is given
        and a bit smaller race if a Str is given, as the $*CWD is used
        during coersion and not in body

src/core/IO/Path.pm

@@ -239,8 +239,18 @@ my class IO::Path is Cool {
     }
 
     proto method chdir(|) { * }
-    multi method chdir(IO::Path:D: Str() $path is copy, :$test = 'r') {
-        if !$!SPEC.is-absolute($path) {
+    multi method chdir(IO::Path:D: Str() $path, :$test!) {
+        DEPRECATED(
+            :what<:$test argument>,
+            'individual named parameters (e.g. :r, :w, :x)',
+            "v2017.03.101.ga.5800.a.1", "v6.d", :up(*),
+        );
+        self.chdir: $path, |$test.words.map(* => True).Hash;
+    }
+    multi method chdir(
+        IO::Path:D: Str() $path is copy, :$d = True, :$r, :$w, :$x,
+    ) {
+        unless $!SPEC.is-absolute($path) {
             my ($volume,$dirs) = $!SPEC.splitpath(self.abspath, :nofile);
             my @dirs = $!SPEC.splitdir($dirs);
             @dirs.shift; # the first is always empty for absolute dirs
@@ -257,30 +267,27 @@ my class IO::Path is Cool {
         }
         my $dir = IO::Path.new-from-absolute-path($path,:$!SPEC,:CWD(self));
 
-        # basic sanity
-        unless $dir.d {
-            fail X::IO::Chdir.new(
-              :$path,
-              :os-error( $dir.e
-                ?? "is not a directory"
-                !! "does not exist"),
-            );
-        }
-
-        if $test eq 'r' {
-            return $dir if $dir.r;
-        }
-        elsif $test eq 'r w' {
-            return $dir if $dir.r and $dir.w;
-        }
-        elsif $test eq 'r w x' {
-            return $dir if $dir.r and $dir.w and $dir.x;
-        }
-
-        fail X::IO::Chdir.new(
-          :$path,
-          :os-error("did not pass 'd $test' test"),
-        );
+        nqp::stmts(
+            nqp::unless(
+                nqp::unless(nqp::isfalse($d), $dir.d),
+                fail X::IO::Chdir.new: :$path, :os-error(
+                    nqp::if($dir.e, 'is not a directory', 'does not exist')
+                )
+            ),
+            nqp::unless(
+                nqp::unless(nqp::isfalse($r), $dir.r),
+                fail X::IO::Chdir.new: :$path, :os-error("did not pass :r test")
+            ),
+            nqp::unless(
+                nqp::unless(nqp::isfalse($w), $dir.w),
+                fail X::IO::Chdir.new: :$path, :os-error("did not pass :w test")
+            ),
+            nqp::unless(
+                nqp::unless(nqp::isfalse($x), $dir.x),
+                fail X::IO::Chdir.new: :$path, :os-error("did not pass :x test")
+            ),
+            $dir
+        )
     }
 
     proto method rename(|) { * }

src/core/io_operators.pm

@@ -161,20 +161,16 @@ multi sub spurt(Cool $path, $contents, |c) {
     PROCESS::<&chdir> := &chdir;
 }
 
-sub chdir(Str() $path, :$test = 'r') {
-    my $newCWD := $*CWD.chdir($path,:$test);
-    $newCWD // $newCWD.throw;
-
-    $*CWD = $newCWD;
-}
-
-sub indir(Str() $path, $what, :$test = <r w>) {
-    my $newCWD := $*CWD.chdir($path,:$test);
-    $newCWD // $newCWD.throw;
-
-    {
-        my $*CWD = $newCWD;  # temp doesn't work in core settings :-(
-        $what();
+sub chdir(|c) { $*CWD .= chdir(|c) }
+sub indir(IO() $path, &what, |c) {
+    {   # NOTE: we need this extra block so that the IO() coercer doesn't
+        # use our (empty at the time) $*CWD when making the IO::Path object
+
+        # We call .chdir for the sake of its doing the :d:r:w:x tests
+        nqp::if(
+            nqp::istype((my $*CWD = $path.chdir($path,|c)), Failure),
+            $*CWD, what,
+        )
     }
 }