git-gui: Generate blame on uncommitted working tree file

If the user doesn't give us a revision parameter to our blame
subcommand then we can generate blame against the working tree
file by passing the file path off to blame with the --contents
argument.  In this case we cannot obtain the contents of the
file from the ODB; instead we must obtain the contents by
reading the working directory file as-is.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -1605,6 +1605,7 @@ browser {
 }
 blame {
 	set subcommand_args {rev? path?}
+	set head {}
 	set path {}
 	set is_path 0
 	foreach a $argv {
@@ -1614,27 +1615,30 @@ blame {
 			break
 		} elseif {$a eq {--}} {
 			if {$path ne {}} {
-				if {$current_branch ne {}} usage
-				set current_branch $path
+				if {$head ne {}} usage
+				set head $path
 				set path {}
 			}
 			set is_path 1
-		} elseif {$current_branch eq {}} {
-			if {$current_branch ne {}} usage
-			set current_branch $a
+		} elseif {$head eq {}} {
+			if {$head ne {}} usage
+			set head $a
 		} else {
 			usage
 		}
 	}
 	unset is_path
 
-	if {$current_branch eq {} && $path ne {}} {
+	if {$head eq {}} {
 		set current_branch [git symbolic-ref HEAD]
 		regsub ^refs/((heads|tags|remotes)/)? \
 			$current_branch {} current_branch
+	} else {
+		set current_branch $head
 	}
-	if {$current_branch eq {} || $path eq {}} usage
-	blame::new $current_branch $path
+
+	if {$path eq {}} usage
+	blame::new $head $path
 	return
 }
 citool -

lib/blame.tcl

@@ -170,8 +170,12 @@ constructor new {i_commit i_path} {
 	bind $top <Visibility> "focus $top"
 	bind $top <Destroy> [list delete_this $this]
 
-	set cmd [list git cat-file blob "$commit:$path"]
-	set fd [open "| $cmd" r]
+	if {$commit eq {}} {
+		set fd [open $path r]
+	} else {
+		set cmd [list git cat-file blob "$commit:$path"]
+		set fd [open "| $cmd" r]
+	}
 	fconfigure $fd -blocking 0 -translation lf -encoding binary
 	fileevent $fd readable [cb _read_file $fd]
 }
@@ -194,7 +198,13 @@ method _read_file {fd} {
 	if {[eof $fd]} {
 		close $fd
 		_status $this
-		set cmd [list git blame -M -C --incremental $commit -- $path]
+		set cmd [list git blame -M -C --incremental]
+		if {$commit eq {}} {
+			lappend cmd --contents $path
+		} else {
+			lappend cmd $commit
+		}
+		lappend cmd -- $path
 		set fd [open "| $cmd" r]
 		fconfigure $fd -blocking 0 -translation lf -encoding binary
 		fileevent $fd readable [cb _read_blame $fd]