git-gui: revert untracked files by deleting them

Update the revert_helper proc to check for untracked files as well as
changes, and then handle changes to be reverted and untracked files with
independent blocks of code. Prompt the user independently for untracked
files, since the underlying action is fundamentally different (rm -f).
If after deleting untracked files, the directory containing them becomes
empty, then remove the directory as well. Migrate unlocking of the index
out of _close_updateindex to a responsibility of the caller, to permit
paths that don't directly unlock the index, and refactor the error
handling added in d4e890e so that callers can make flow control
decisions in the event of errors. Update Tcl/Tk dependency from 8.4 to
8.6 in git-gui.sh.

A new proc delete_files takes care of actually deleting the files in
batches, using the Tcler's Wiki recommended approach for keeping the UI
responsive.

Since the checkout_index and delete_files calls are both asynchronous
and could potentially complete in any order, a "chord" is used to
coordinate unlocking the index and returning the UI to a usable state
only after both operations are complete. The `SimpleChord` class,
based on TclOO (Tcl/Tk 8.6), is added in this commit.

Signed-off-by: Jonathan Gilbert <JonathanG@iQmetrix.com>
Signed-off-by: Pratyush Yadav <me@yadavpratyush.com>

git-gui.sh

@@ -30,8 +30,8 @@ along with this program; if not, see <http://www.gnu.org/licenses/>.}]
 ##
 ## Tcl/Tk sanity check
 
-if {[catch {package require Tcl 8.4} err]
- || [catch {package require Tk  8.4} err]
+if {[catch {package require Tcl 8.6} err]
+ || [catch {package require Tk  8.6} err]
 } {
 	catch {wm withdraw .}
 	tk_messageBox \

lib/chord.tcl

@@ -0,0 +1,160 @@
+# Simple Chord for Tcl
+#
+# A "chord" is a method with more than one entrypoint and only one body, such
+# that the body runs only once all the entrypoints have been called by
+# different asynchronous tasks. In this implementation, the chord is defined
+# dynamically for each invocation. A SimpleChord object is created, supplying
+# body script to be run when the chord is completed, and then one or more notes
+# are added to the chord. Each note can be called like a proc, and returns
+# immediately if the chord isn't yet complete. When the last remaining note is
+# called, the body runs before the note returns.
+#
+# The SimpleChord class has a constructor that takes the body script, and a
+# method add_note that returns a note object. Since the body script does not
+# run in the context of the procedure that defined it, a mechanism is provided
+# for injecting variables into the chord for use by the body script. The
+# activation of a note is idempotent; multiple calls have the same effect as
+# a simple call.
+#
+# If you are invoking asynchronous operations with chord notes as completion
+# callbacks, and there is a possibility that earlier operations could complete
+# before later ones are started, it is a good practice to create a "common"
+# note on the chord that prevents it from being complete until you're certain
+# you've added all the notes you need.
+#
+# Example:
+#
+#   # Turn off the UI while running a couple of async operations.
+#   lock_ui
+#
+#   set chord [SimpleChord new {
+#     unlock_ui
+#     # Note: $notice here is not referenced in the calling scope
+#     if {$notice} { info_popup $notice }
+#   }
+#
+#   # Configure a note to keep the chord from completing until
+#   # all operations have been initiated.
+#   set common_note [$chord add_note]
+#
+#   # Pass notes as 'after' callbacks to other operations
+#   async_operation $args [$chord add_note]
+#   other_async_operation $args [$chord add_note]
+#
+#   # Communicate with the chord body
+#   if {$condition} {
+#     # This sets $notice in the same context that the chord body runs in.
+#     $chord eval { set notice "Something interesting" }
+#   }
+#
+#   # Activate the common note, making the chord eligible to complete
+#   $common_note
+#
+# At this point, the chord will complete at some unknown point in the future.
+# The common note might have been the first note activated, or the async
+# operations might have completed synchronously and the common note is the
+# last one, completing the chord before this code finishes, or anything in
+# between. The purpose of the chord is to not have to worry about the order.
+
+# SimpleChord class:
+#   Represents a procedure that conceptually has multiple entrypoints that must
+#   all be called before the procedure executes. Each entrypoint is called a
+#   "note". The chord is only "completed" when all the notes are "activated".
+oo::class create SimpleChord {
+	variable notes body is_completed
+
+	# Constructor:
+	#   set chord [SimpleChord new {body}]
+	#     Creates a new chord object with the specified body script. The
+	#     body script is evaluated at most once, when a note is activated
+	#     and the chord has no other non-activated notes.
+	constructor {body} {
+		set notes [list]
+		my eval [list set body $body]
+		set is_completed 0
+	}
+
+	# Method:
+	#   $chord eval {script}
+	#     Runs the specified script in the same context (namespace) in which
+	#     the chord body will be evaluated. This can be used to set variable
+	#     values for the chord body to use.
+	method eval {script} {
+		namespace eval [self] $script
+	}
+
+	# Method:
+	#   set note [$chord add_note]
+	#     Adds a new note to the chord, an instance of ChordNote. Raises an
+	#     error if the chord is already completed, otherwise the chord is
+	#     updated so that the new note must also be activated before the
+	#     body is evaluated.
+	method add_note {} {
+		if {$is_completed} { error "Cannot add a note to a completed chord" }
+
+		set note [ChordNote new [self]]
+
+		lappend notes $note
+
+		return $note
+	}
+
+	# This method is for internal use only and is intentionally undocumented.
+	method notify_note_activation {} {
+		if {!$is_completed} {
+			foreach note $notes {
+				if {![$note is_activated]} { return }
+			}
+
+			set is_completed 1
+
+			namespace eval [self] $body
+			namespace delete [self]
+		}
+	}
+}
+
+# ChordNote class:
+#   Represents a note within a chord, providing a way to activate it. When the
+#   final note of the chord is activated (this can be any note in the chord,
+#   with all other notes already previously activated in any order), the chord's
+#   body is evaluated.
+oo::class create ChordNote {
+	variable chord is_activated
+
+	# Constructor:
+	#   Instances of ChordNote are created internally by calling add_note on
+	#   SimpleChord objects.
+	constructor {chord} {
+		my eval set chord $chord
+		set is_activated 0
+	}
+
+	# Method:
+	#   [$note is_activated]
+	#     Returns true if this note has already been activated.
+	method is_activated {} {
+		return $is_activated
+	}
+
+	# Method:
+	#   $note
+	#     Activates the note, if it has not already been activated, and
+	#     completes the chord if there are no other notes awaiting
+	#     activation. Subsequent calls will have no further effect.
+	#
+	# NB: In TclOO, if an object is invoked like a method without supplying
+	#     any method name, then this internal method `unknown` is what
+	#     actually runs (with no parameters). It is used in the ChordNote
+	#     class for the purpose of allowing the note object to be called as
+	#     a function (see example above). (The `unknown` method can also be
+	#     used to support dynamic dispatch, but must take parameters to
+	#     identify the "unknown" method to be invoked. In this form, this
+	#     proc serves only to make instances behave directly like methods.)
+	method unknown {} {
+		if {!$is_activated} {
+			set is_activated 1
+			$chord notify_note_activation
+		}
+	}
+}