Improved CDPATH (#644)

This updated `c` command supports:
* Changing to the previous directory with `c -`
* Changing to absolute directories
* Completion of CDPATH entries
* Completion of absolute paths
* Completion of children

When completing CDPATH entries the parent directory is shown to provide
context in case multiple CDPATH entries have the same child directory
names.

Fixes #244

sourced/filesystem/cdpath.nu

@@ -1,36 +1,169 @@
-def-env c [dir = ""] {
-    let default = if $nu.os-info.name == "windows" {
+# You must set $env.CDPATH, try:
+#
+#     $env.CDPATH = [
+#       ".",
+#       "~",
+#       "~/path/to/repositories",
+#     ]
+#
+# The above $env.CDPATH will complete:
+# * Entries under the current directory ($env.PWD)
+# * Entries in your home directory ($env.HOME)
+# * Entries where you check out repositories
+# * Children of those entries
+#
+# This CDPATH implementation also completes absolute paths to help you use `c`
+# instead of `cd`
+#
+# Bugs:
+# * `c` does not complete paths that start with "~".  This should support both
+#   directories ("~/.config/nu"), users ("~notme"), and both combined
+#   ("~notme/.config/nu")
+module cdpath {
+  # $env.CDPATH with unique, expanded, existing paths
+  def cdpath [] {
+    $env.CDPATH
+    | path expand
+    | uniq
+    | filter {|| $in | path exists }
+  }
+
+  # Children of a path
+  def children [path: string] {
+    ls -a $path
+    | where type == "dir"
+    | get name
+  }
+
+  # Completion for `c`
+  #
+  # `contains` is used instead of `starts-with` to behave similar to fuzzy
+  # completion behavior.
+  #
+  # During completion of a CDPATH entry the description contains the parent
+  # directory you will complete under.  This allows you to tell which entry in
+  # your CDPATH your are completing to if you have the same directory under
+  # multiple entries.
+  def complete [context: string] {
+    let context_dir = $context | parse "c {context_dir}" | get context_dir | first
+    let path = $context_dir | path split
+    let no_trailing_slash = not ($context_dir | str ends-with "/")
+
+    # completion with no context
+    if ( $path | is-empty ) {
+      complete_from_cdpath
+    # Complete an entry in CDPATH
+    #
+    # This appends a / to allow continuation to the last step
+    } else if $no_trailing_slash and (1 == ( $path | length )) {
+      let first = $path | first
+
+      complete_from_cdpath
+      | filter {|| $in.value | str contains $first }
+      | upsert value {|| $"($in.value)/" }
+    # Complete a child of a CDPATH entry
+    } else {
+      let prefix = if 1 == ($path | length) {
+        $path | first
+      } else {
+        $path | first (($path | length) - 1) | path join
+      }
+
+      let last = if 1 == ($path | length) {
+        ""
+      } else {
+        $path | last
+      }
+
+      let chosen_path = if ( $path | first) == "/" {
+        if $no_trailing_slash {
+          $prefix
+        } else {
+          $context_dir
+        }
+      } else {
+        cdpath
+        | each {||
+          $in | path join $prefix
+        }
+        | filter {||
+          $in | path exists
+        }
+        | first
+      }
+
+      children $chosen_path
+      | filter {||
+        $in | str contains $last
+      }
+      | each {|child|
+        $"($chosen_path | path join $child)/"
+      }
+    }
+  }
+
+  def complete_from_cdpath [] {
+    cdpath
+    | each { |path|
+      children $path
+      | path basename
+      | sort
+      | each { |child| { value: $child, description: $path } }
+    }
+    | flatten
+    | uniq-by value
+  }
+
+  # Change directory with $env.CDPATH
+  export def-env c [dir = "": string@complete] {
+    let span = (metadata $dir).span
+      let default = if $nu.os-info.name == "windows" {
         $env.USERPROFILE
-    } else {
+      } else {
         $env.HOME
-    }
+      }
 
-    let complete_dir = if $dir == "" {
+    let target_dir = if $dir == "" {
+      $default
+    } else if $dir == "-" {
+      if "OLDPWD" in $env {
+        $env.OLDPWD
+      } else {
         $default
+      }
     } else {
-        $env.CDPATH
-        | reduce -f "" { |$it, $acc| if $acc == "" {
-            let new_path = ([$it $dir] | path join)
+      cdpath
+      | reduce -f "" { |$it, $acc|
+        if $acc == "" {
+          let new_path = ([$it $dir] | path join)
             if ($new_path | path exists) {
-                $new_path
+              $new_path
             } else {
-                ""
+              ""
             }
-        } else { $acc }}
-    }
-    
-    let complete_dir = if $complete_dir == "" { 
-        error make --unspanned {msg: "No such path"} 
-    } else if (($complete_dir | path expand | path type) != "dir") {
-        error make --unspanned {msg: "Not a directory"}
-    } else { 
-        ($complete_dir | path expand)
+        } else {
+          $acc
+        }
+      }
     }
 
-    cd $complete_dir
+    let target_dir = if $target_dir == "" {
+      let cdpath = $env.CDPATH | str join ", "
+
+      error make {
+        msg: $"No such child under: ($cdpath)",
+        label: {
+          text: "Child directory",
+          start: $span.start,
+          end: $span.end,
+        }
+      }
+    } else {
+      $target_dir
+    }
+
+    cd $target_dir
+  }
 }
 
-# You need to have $env.CDPATH variable declared, my suggestion from config.nu:
-# $env.CDPATH = [".", $env.HOME, "/", ([$env.HOME, ".config"] | path join)]
-# WINDOWS:
-# $env.CDPATH = ["", $env.USERPROFILE, ([$env.USERPROFILE, "AppData\\Roaming\\"] | path join)]
+use cdpath c