gitk: Clean up file encoding code and add enable/disable option

This adds an option allowing the user to select whether gitk should
look up per-file encoding settings using git check-attr or not.  If
not, gitk uses the global encoding set in the git config (as reported
by git config --get gui.encoding) for all files, or if that is not
set, then the system encoding.

The option is controlled by a checkbox in the Edit->Preferences
window, and defaults to off for now because git check-attr is so
slow.  When the user turns it on we discard any cached diff file
lists in treediffs, because we may not have encodings cached for
the files listed in those lists, meaning that getblobdiffline will
do it for each file, which will be really really slow.

This adjusts the limit of how many paths cache_gitattr passes to each
instance of git check-attr depending on whether we're running under
windows or not.  Passing only 30 doesn't effectively amortize the
startup costs of git check-attr, but it's all we can do under windows
because of the 32k limit on arguments to a command.  Under other OSes
we pass up to 1000.

Similarly we adjust how many lines gettreediffline processes depending
on whether we are doing per-file encodings so that we don't run for
too long.  When we are, 500 seems to be a reasonable limit, leading
to gettreediffline taking about 60-70ms under Linux (almost all of
which is in cache_gitattr, unfortunately).  This means that we can
take out the update call in cache_gitattr.

This adds a simple cache on [tclencoding].  Now that we get repeated
calls to translate the same encoding, this is useful.

This reindents the new code added in the last couple of commits to
conform to the gitk 4-space indent and makes various other improvements:
use regexp in gitattr and cache_gitattr instead of split + join + regsub,
make gui_encoding be the value from [tclencoding] to avoid having to
do [tcl_encoding $gui_encoding] in each call to get_path_encoding,
and print a warning message at startup if $gui_encoding isn't
supported by Tcl.

Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -2332,7 +2332,7 @@ proc savestuff {w} {
     global viewname viewfiles viewargs viewargscmd viewperm nextviewnum
     global cmitmode wrapcomment datetimeformat limitdiffs
     global colors bgcolor fgcolor diffcolors diffcontext selectbgcolor
-    global autoselect extdifftool
+    global autoselect extdifftool perfile_attrs
 
     if {$stuffsaved} return
     if {![winfo viewable .]} return
@@ -2359,6 +2359,7 @@ proc savestuff {w} {
 	puts $f [list set diffcontext $diffcontext]
 	puts $f [list set selectbgcolor $selectbgcolor]
 	puts $f [list set extdifftool $extdifftool]
+	puts $f [list set perfile_attrs $perfile_attrs]
 
 	puts $f "set geometry(main) [wm geometry .]"
 	puts $f "set geometry(topwidth) [winfo width .tf]"
@@ -6528,11 +6529,20 @@ proc gettreediffs {ids} {
 
 proc gettreediffline {gdtf ids} {
     global treediff treediffs treepending diffids diffmergeid
-    global cmitmode vfilelimit curview limitdiffs
+    global cmitmode vfilelimit curview limitdiffs perfile_attrs
 
     set nr 0
     set sublist {}
-    while {[incr nr] <= 1000 && [gets $gdtf line] >= 0} {
+    set max 1000
+    if {$perfile_attrs} {
+	# cache_gitattr is slow, and even slower on win32 where we
+	# have to invoke it for only about 30 paths at a time
+	set max 500
+	if {[tk windowingsystem] == "win32"} {
+	    set max 120
+	}
+    }
+    while {[incr nr] <= $max && [gets $gdtf line] >= 0} {
 	set i [string first "\t" $line]
 	if {$i >= 0} {
 	    set file [string range $line [expr {$i+1}] end]
@@ -6544,9 +6554,11 @@ proc gettreediffline {gdtf ids} {
 	    lappend sublist $file
 	}
     }
-    cache_gitattr encoding $sublist
+    if {$perfile_attrs} {
+	cache_gitattr encoding $sublist
+    }
     if {![eof $gdtf]} {
-	return [expr {$nr >= 1000? 2: 1}]
+	return [expr {$nr >= $max? 2: 1}]
     }
     close $gdtf
     if {$limitdiffs && $vfilelimit($curview) ne {}} {
@@ -9318,7 +9330,7 @@ proc doprefs {} {
     global maxwidth maxgraphpct
     global oldprefs prefstop showneartags showlocalchanges
     global bgcolor fgcolor ctext diffcolors selectbgcolor
-    global tabstop limitdiffs autoselect extdifftool
+    global tabstop limitdiffs autoselect extdifftool perfile_attrs
 
     set top .gitkprefs
     set prefstop $top
@@ -9327,7 +9339,7 @@ proc doprefs {} {
 	return
     }
     foreach v {maxwidth maxgraphpct showneartags showlocalchanges \
-		   limitdiffs tabstop} {
+		   limitdiffs tabstop perfile_attrs} {
 	set oldprefs($v) [set $v]
     }
     toplevel $top
@@ -9369,6 +9381,11 @@ proc doprefs {} {
     checkbutton $top.ldiff.b -variable limitdiffs
     pack $top.ldiff.b $top.ldiff.l -side left
     grid x $top.ldiff -sticky w
+    frame $top.lattr
+    label $top.lattr.l -text [mc "Support per-file encodings"] -font optionfont
+    checkbutton $top.lattr.b -variable perfile_attrs
+    pack $top.lattr.b $top.lattr.l -side left
+    grid x $top.lattr -sticky w
 
     entry $top.extdifft -textvariable extdifftool
     frame $top.extdifff
@@ -9478,7 +9495,7 @@ proc prefscan {} {
     global oldprefs prefstop
 
     foreach v {maxwidth maxgraphpct showneartags showlocalchanges \
-		   limitdiffs tabstop} {
+		   limitdiffs tabstop perfile_attrs} {
 	global $v
 	set $v $oldprefs($v)
     }
@@ -9491,7 +9508,7 @@ proc prefsok {} {
     global maxwidth maxgraphpct
     global oldprefs prefstop showneartags showlocalchanges
     global fontpref mainfont textfont uifont
-    global limitdiffs treediffs
+    global limitdiffs treediffs perfile_attrs
 
     catch {destroy $prefstop}
     unset prefstop
@@ -9524,8 +9541,10 @@ proc prefsok {} {
 	    dohidelocalchanges
 	}
     }
-    if {$limitdiffs != $oldprefs(limitdiffs)} {
-	# treediffs elements are limited by path
+    if {$limitdiffs != $oldprefs(limitdiffs) ||
+	($perfile_attrs && !$oldprefs(perfile_attrs))} {
+	# treediffs elements are limited by path;
+	# won't have encodings cached if perfile_attrs was just turned on
 	catch {unset treediffs}
     }
     if {$fontchanged || $maxwidth != $oldprefs(maxwidth)
@@ -9784,7 +9803,10 @@ set encoding_aliases {
 }
 
 proc tcl_encoding {enc} {
-    global encoding_aliases
+    global encoding_aliases tcl_encoding_cache
+    if {[info exists tcl_encoding_cache($enc)]} {
+	return $tcl_encoding_cache($enc)
+    }
     set names [encoding names]
     set lcnames [string tolower $names]
     set enc [string tolower $enc]
@@ -9812,68 +9834,70 @@ proc tcl_encoding {enc} {
 	    break
 	}
     }
+    set tclenc {}
     if {$i >= 0} {
-	return [lindex $names $i]
+	set tclenc [lindex $names $i]
     }
-    return {}
+    set tcl_encoding_cache($enc) $tclenc
+    return $tclenc
 }
 
 proc gitattr {path attr default} {
-	global path_attr_cache
-	if {[info exists path_attr_cache($attr,$path)]} {
-		set r $path_attr_cache($attr,$path)
-	} elseif {[catch {set r [exec git check-attr $attr -- $path]}]} {
-		set r unspecified
-	} else {
-		set r [join [lrange [split $r :] 2 end] :]
-		regsub {^ } $r {} r
+    global path_attr_cache
+    if {[info exists path_attr_cache($attr,$path)]} {
+	set r $path_attr_cache($attr,$path)
+    } else {
+	set r "unspecified"
+	if {![catch {set line [exec git check-attr $attr -- $path]}]} {
+	    regexp "(.*): encoding: (.*)" $line m f r
 	}
 	set path_attr_cache($attr,$path) $r
-	if {$r eq {unspecified}} {
-		return $default
-	}
-	return $r
+    }
+    if {$r eq "unspecified"} {
+	return $default
+    }
+    return $r
 }
 
 proc cache_gitattr {attr pathlist} {
-	global path_attr_cache
-	set newlist {}
-	foreach path $pathlist {
-		if {[info exists path_attr_cache($attr,$path)]} continue
-		lappend newlist $path
-	}
-	while {$newlist ne {}} {
-		set head [lrange $newlist 0 29]
-		set newlist [lrange $newlist 30 end]
-		if {![catch {set rlist [eval exec git check-attr $attr -- $head]}]} {
-			foreach row [split $rlist "\n"] {
-				set cols [split $row :]
-				set path [lindex $cols 0]
-				set value [join [lrange $cols 2 end] :]
-				if {[string index $path 0] eq "\""} {
-					set path [encoding convertfrom [lindex $path 0]]
-				}
-				regsub {^ } $value {} value
-				set path_attr_cache($attr,$path) $value
-			}
+    global path_attr_cache
+    set newlist {}
+    foreach path $pathlist {
+	if {![info exists path_attr_cache($attr,$path)]} {
+	    lappend newlist $path
+	}
+    }
+    set lim 1000
+    if {[tk windowingsystem] == "win32"} {
+	# windows has a 32k limit on the arguments to a command...
+	set lim 30
+    }
+    while {$newlist ne {}} {
+	set head [lrange $newlist 0 [expr {$lim - 1}]]
+	set newlist [lrange $newlist $lim end]
+	if {![catch {set rlist [eval exec git check-attr $attr -- $head]}]} {
+	    foreach row [split $rlist "\n"] {
+		if {[regexp "(.*): encoding: (.*)" $row m path value]} {
+		    if {[string index $path 0] eq "\""} {
+			set path [encoding convertfrom [lindex $path 0]]
+		    }
+		    set path_attr_cache($attr,$path) $value
 		}
-		update
+	    }
 	}
+    }
 }
 
 proc get_path_encoding {path} {
-	global gui_encoding
-	set tcl_enc [tcl_encoding $gui_encoding]
-	if {$tcl_enc eq {}} {
-		set tcl_enc [encoding system]
-	}
-	if {$path ne {}} {
-		set enc2 [tcl_encoding [gitattr $path encoding $tcl_enc]]
-		if {$enc2 ne {}} {
-			set tcl_enc $enc2
-		}
+    global gui_encoding perfile_attrs
+    set tcl_enc $gui_encoding
+    if {$path ne {} && $perfile_attrs} {
+	set enc2 [tcl_encoding [gitattr $path encoding $tcl_enc]]
+	if {$enc2 ne {}} {
+	    set tcl_enc $enc2
 	}
-	return $tcl_enc
+    }
+    return $tcl_enc
 }
 
 # First check that Tcl/Tk is recent enough
@@ -9900,7 +9924,15 @@ if {$tclencoding == {}} {
 
 set gui_encoding [encoding system]
 catch {
-	set gui_encoding [exec git config --get gui.encoding]
+    set enc [exec git config --get gui.encoding]
+    if {$enc ne {}} {
+	set tclenc [tcl_encoding $enc]
+	if {$tclenc ne {}} {
+	    set gui_encoding $tclenc
+	} else {
+	    puts stderr "Warning: encoding $enc is not supported by Tcl/Tk"
+	}
+    }
 }
 
 set mainfont {Helvetica 9}
@@ -9924,6 +9956,7 @@ set showlocalchanges 1
 set limitdiffs 1
 set datetimeformat "%Y-%m-%d %H:%M:%S"
 set autoselect 1
+set perfile_attrs 0
 
 set extdifftool "meld"