git-gui: Better positioning in Blame Parent Commit

Invoke diff-tree between the commit and its parent,
and use the hunks to fix the target line number,
accounting for addition and removal of lines.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

diff --git a/lib/blame.tcl b/lib/blame.tcl
index ef4223179358857299af190c172436f57394146b..1106975775e86cea028b42977521ea255d698468 100644 (file)
--- a/lib/blame.tcl
+++ b/lib/blame.tcl
@@ -984,19 +984,76 @@ method _blameparent {} {
        set dat [_get_click_amov_info $this]
        if {$dat ne {}} {
                set cmit [lindex $dat 0]
+               set new_path [lindex $dat 1]
 
                if {[catch {set cparent [git rev-parse --verify "$cmit^"]}]} {
                        error_popup [strcat [mc "Cannot find parent commit:"] "\n\n$err"]
                        return;
                }
 
-               _load_new_commit $this  \
-                       $cparent \
-                       [lindex $dat 1] \
-                       [list [lindex $dat 2]]
+               _kill $this
+
+               # Generate a diff between the commit and its parent,
+               # and use the hunks to update the line number.
+               # Request zero context to simplify calculations.
+               if {[catch {set fd [eval git_read diff-tree \
+                               --unified=0 $cparent $cmit $new_path]} err]} {
+                       $status stop [mc "Unable to display parent"]
+                       error_popup [strcat [mc "Error loading diff:"] "\n\n$err"]
+                       return
+               }
+
+               set r_orig_line [lindex $dat 2]
+
+               fconfigure $fd \
+                       -blocking 0 \
+                       -encoding binary \
+                       -translation binary
+               fileevent $fd readable [cb _read_diff_load_commit \
+                       $fd $cparent $new_path $r_orig_line]
+               set current_fd $fd
        }
 }
 
+method _read_diff_load_commit {fd cparent new_path tline} {
+       if {$fd ne $current_fd} {
+               catch {close $fd}
+               return
+       }
+
+       while {[gets $fd line] >= 0} {
+               if {[regexp {^@@ -(\d+)(,(\d+))? \+(\d+)(,(\d+))? @@} $line line \
+                       old_line osz old_size new_line nsz new_size]} {
+
+                       if {$osz eq {}} { set old_size 1 }
+                       if {$nsz eq {}} { set new_size 1 }
+
+                       if {$new_line <= $tline} {
+                               if {[expr {$new_line + $new_size}] > $tline} {
+                                       # Target line within the hunk
+                                       set line_shift [expr {
+                                               ($new_size-$old_size)*($tline-$new_line)/$new_size
+                                               }]
+                               } else {
+                                       set line_shift [expr {$new_size-$old_size}]
+                               }
+
+                               set r_orig_line [expr {$r_orig_line - $line_shift}]
+                       }
+               }
+       }
+
+       if {[eof $fd]} {
+               close $fd;
+               set current_fd {}
+
+               _load_new_commit $this  \
+                       $cparent        \
+                       $new_path       \
+                       [list $r_orig_line]
+       }
+} ifdeleted { catch {close $fd} }
+
 method _show_tooltip {cur_w pos} {
        if {$tooltip_wm ne {}} {
                _open_tooltip $this $cur_w