gitk: Work around Tcl's non-standard names for encodings

This uses a table of encoding names and aliases distilled from
http://www.iana.org/assignments/character-sets plus some heuristics
to convert standard encoding names to ones that Tcl recognizes.

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

diff --git a/gitk b/gitk
index 2e94145021afd56c995e6ee58dc8a40538996255..f12b3ce20928b0228a2b10696db5e16e96f64cc0 100755 (executable)
--- a/gitk
+++ b/gitk
@@ -34,7 +34,7 @@ proc parse_args {rargs} {
 
 proc start_rev_list {rlargs} {
     global startmsecs nextupdate ncmupdate
-    global commfd leftover gitencoding
+    global commfd leftover tclencoding
 
     set startmsecs [clock clicks -milliseconds]
     set nextupdate [expr {$startmsecs + 100}]
@@ -47,7 +47,10 @@ proc start_rev_list {rlargs} {
        exit 1
     }
     set leftover {}
-    fconfigure $commfd -blocking 0 -translation lf -encoding $gitencoding
+    fconfigure $commfd -blocking 0 -translation lf
+    if {$tclencoding != {}} {
+       fconfigure $commfd -encoding $tclencoding
+    }
     fileevent $commfd readable [list getcommitlines $commfd]
     . config -cursor watch
     settextcursor watch
@@ -182,6 +185,96 @@ proc readcommit {id} {
     parsecommit $id $contents 0 {}
 }
 
+proc updatecommits {rargs} {
+    global commitlisted commfd phase
+    global startmsecs nextupdate ncmupdate
+    global idtags idheads idotherrefs
+    global leftover
+    global parsed_args
+    global canv mainfont
+    global oldcommits commits
+    global parents nchildren children ncleft
+
+    set old_args $parsed_args
+    parse_args $rargs
+
+    if {$phase == "getcommits" || $phase == "incrdraw"} {
+       # havent read all the old commits, just start again from scratch
+       stopfindproc
+       set oldcommits {}
+       set commits {}
+       foreach v {children nchildren parents commitlisted commitinfo
+                  selectedline matchinglines treediffs
+                  mergefilelist currentid rowtextx} {
+           global $v
+           catch {unset $v}
+       }
+       readrefs
+       if {$phase == "incrdraw"} {
+           allcanvs delete all
+           $canv create text 3 3 -anchor nw -text "Reading commits..." \
+               -font $mainfont -tags textitems
+           set phase getcommits
+       }
+       start_rev_list $parsed_args
+       return
+    }
+
+    foreach id $old_args {
+       if {![regexp {^[0-9a-f]{40}$} $id]} continue
+       if {[info exists oldref($id)]} continue
+       set oldref($id) $id
+       lappend ignoreold "^$id"
+    }
+    foreach id $parsed_args {
+       if {![regexp {^[0-9a-f]{40}$} $id]} continue
+       if {[info exists ref($id)]} continue
+       set ref($id) $id
+       lappend ignorenew "^$id"
+    }
+
+    foreach a $old_args {
+       if {![info exists ref($a)]} {
+           lappend ignorenew $a
+       }
+    }
+
+    set phase updatecommits
+    set oldcommits $commits
+    set commits {}
+    set removed_commits [split [eval exec git-rev-list $ignorenew] "\n" ]
+    if {[llength $removed_commits] > 0} {
+       allcanvs delete all
+       foreach c $removed_commits {
+           set i [lsearch -exact $oldcommits $c]
+           if {$i >= 0} {
+               set oldcommits [lreplace $oldcommits $i $i]
+               unset commitlisted($c)
+               foreach p $parents($c) {
+                   if {[info exists nchildren($p)]} {
+                       set j [lsearch -exact $children($p) $c]
+                       if {$j >= 0} {
+                           set children($p) [lreplace $children($p) $j $j]
+                           incr nchildren($p) -1
+                       }
+                   }
+               }
+           }
+       }
+       set phase removecommits
+    }
+
+    set args {}
+    foreach a $parsed_args {
+       if {![info exists oldref($a)]} {
+           lappend args $a
+       }
+    }
+
+    readrefs
+    start_rev_list [concat $ignoreold $args]
+}
+
 proc updatechildren {id olds} {
     global children nchildren parents nparents ncleft
 
@@ -3624,96 +3717,6 @@ proc rereadrefs {} {
     }
 }
 
-proc updatecommits {rargs} {
-    global commitlisted commfd phase
-    global startmsecs nextupdate ncmupdate
-    global idtags idheads idotherrefs
-    global leftover
-    global parsed_args
-    global canv mainfont
-    global oldcommits commits
-    global parents nchildren children ncleft
-
-    set old_args $parsed_args
-    parse_args $rargs
-
-    if {$phase == "getcommits" || $phase == "incrdraw"} {
-       # havent read all the old commits, just start again from scratch
-       stopfindproc
-       set oldcommits {}
-       set commits {}
-       foreach v {children nchildren parents commitlisted commitinfo
-                  selectedline matchinglines treediffs
-                  mergefilelist currentid rowtextx} {
-           global $v
-           catch {unset $v}
-       }
-       readrefs
-       if {$phase == "incrdraw"} {
-           allcanvs delete all
-           $canv create text 3 3 -anchor nw -text "Reading commits..." \
-               -font $mainfont -tags textitems
-           set phase getcommits
-       }
-       start_rev_list $parsed_args
-       return
-    }
-
-    foreach id $old_args {
-       if {![regexp {^[0-9a-f]{40}$} $id]} continue
-       if {[info exists oldref($id)]} continue
-       set oldref($id) $id
-       lappend ignoreold "^$id"
-    }
-    foreach id $parsed_args {
-       if {![regexp {^[0-9a-f]{40}$} $id]} continue
-       if {[info exists ref($id)]} continue
-       set ref($id) $id
-       lappend ignorenew "^$id"
-    }
-
-    foreach a $old_args {
-       if {![info exists ref($a)]} {
-           lappend ignorenew $a
-       }
-    }
-
-    set phase updatecommits
-    set oldcommits $commits
-    set commits {}
-    set removed_commits [split [eval exec git-rev-list $ignorenew] "\n" ]
-    if {[llength $removed_commits] > 0} {
-       allcanvs delete all
-       foreach c $removed_commits {
-           set i [lsearch -exact $oldcommits $c]
-           if {$i >= 0} {
-               set oldcommits [lreplace $oldcommits $i $i]
-               unset commitlisted($c)
-               foreach p $parents($c) {
-                   if {[info exists nchildren($p)]} {
-                       set j [lsearch -exact $children($p) $c]
-                       if {$j >= 0} {
-                           set children($p) [lreplace $children($p) $j $j]
-                           incr nchildren($p) -1
-                       }
-                   }
-               }
-           }
-       }
-       set phase removecommits
-    }
-
-    set args {}
-    foreach a $parsed_args {
-       if {![info exists oldref($a)]} {
-           lappend args $a
-       }
-    }
-
-    readrefs
-    start_rev_list [concat $ignoreold $args]
-}
-
 proc showtag {tag isnew} {
     global ctext cflist tagcontents tagids linknum
 
@@ -3811,17 +3814,294 @@ proc formatdate {d} {
     return [clock format $d -format "%Y-%m-%d %H:%M:%S"]
 }
 
+# This list of encoding names and aliases is distilled from
+# http://www.iana.org/assignments/character-sets.
+# Not all of them are supported by Tcl.
+set encoding_aliases {
+    { ANSI_X3.4-1968 iso-ir-6 ANSI_X3.4-1986 ISO_646.irv:1991 ASCII
+      ISO646-US US-ASCII us IBM367 cp367 csASCII }
+    { ISO-10646-UTF-1 csISO10646UTF1 }
+    { ISO_646.basic:1983 ref csISO646basic1983 }
+    { INVARIANT csINVARIANT }
+    { ISO_646.irv:1983 iso-ir-2 irv csISO2IntlRefVersion }
+    { BS_4730 iso-ir-4 ISO646-GB gb uk csISO4UnitedKingdom }
+    { NATS-SEFI iso-ir-8-1 csNATSSEFI }
+    { NATS-SEFI-ADD iso-ir-8-2 csNATSSEFIADD }
+    { NATS-DANO iso-ir-9-1 csNATSDANO }
+    { NATS-DANO-ADD iso-ir-9-2 csNATSDANOADD }
+    { SEN_850200_B iso-ir-10 FI ISO646-FI ISO646-SE se csISO10Swedish }
+    { SEN_850200_C iso-ir-11 ISO646-SE2 se2 csISO11SwedishForNames }
+    { KS_C_5601-1987 iso-ir-149 KS_C_5601-1989 KSC_5601 korean csKSC56011987 }
+    { ISO-2022-KR csISO2022KR }
+    { EUC-KR csEUCKR }
+    { ISO-2022-JP csISO2022JP }
+    { ISO-2022-JP-2 csISO2022JP2 }
+    { JIS_C6220-1969-jp JIS_C6220-1969 iso-ir-13 katakana x0201-7
+      csISO13JISC6220jp }
+    { JIS_C6220-1969-ro iso-ir-14 jp ISO646-JP csISO14JISC6220ro }
+    { IT iso-ir-15 ISO646-IT csISO15Italian }
+    { PT iso-ir-16 ISO646-PT csISO16Portuguese }
+    { ES iso-ir-17 ISO646-ES csISO17Spanish }
+    { greek7-old iso-ir-18 csISO18Greek7Old }
+    { latin-greek iso-ir-19 csISO19LatinGreek }
+    { DIN_66003 iso-ir-21 de ISO646-DE csISO21German }
+    { NF_Z_62-010_(1973) iso-ir-25 ISO646-FR1 csISO25French }
+    { Latin-greek-1 iso-ir-27 csISO27LatinGreek1 }
+    { ISO_5427 iso-ir-37 csISO5427Cyrillic }
+    { JIS_C6226-1978 iso-ir-42 csISO42JISC62261978 }
+    { BS_viewdata iso-ir-47 csISO47BSViewdata }
+    { INIS iso-ir-49 csISO49INIS }
+    { INIS-8 iso-ir-50 csISO50INIS8 }
+    { INIS-cyrillic iso-ir-51 csISO51INISCyrillic }
+    { ISO_5427:1981 iso-ir-54 ISO5427Cyrillic1981 }
+    { ISO_5428:1980 iso-ir-55 csISO5428Greek }
+    { GB_1988-80 iso-ir-57 cn ISO646-CN csISO57GB1988 }
+    { GB_2312-80 iso-ir-58 chinese csISO58GB231280 }
+    { NS_4551-1 iso-ir-60 ISO646-NO no csISO60DanishNorwegian
+      csISO60Norwegian1 }
+    { NS_4551-2 ISO646-NO2 iso-ir-61 no2 csISO61Norwegian2 }
+    { NF_Z_62-010 iso-ir-69 ISO646-FR fr csISO69French }
+    { videotex-suppl iso-ir-70 csISO70VideotexSupp1 }
+    { PT2 iso-ir-84 ISO646-PT2 csISO84Portuguese2 }
+    { ES2 iso-ir-85 ISO646-ES2 csISO85Spanish2 }
+    { MSZ_7795.3 iso-ir-86 ISO646-HU hu csISO86Hungarian }
+    { JIS_C6226-1983 iso-ir-87 x0208 JIS_X0208-1983 csISO87JISX0208 }
+    { greek7 iso-ir-88 csISO88Greek7 }
+    { ASMO_449 ISO_9036 arabic7 iso-ir-89 csISO89ASMO449 }
+    { iso-ir-90 csISO90 }
+    { JIS_C6229-1984-a iso-ir-91 jp-ocr-a csISO91JISC62291984a }
+    { JIS_C6229-1984-b iso-ir-92 ISO646-JP-OCR-B jp-ocr-b
+      csISO92JISC62991984b }
+    { JIS_C6229-1984-b-add iso-ir-93 jp-ocr-b-add csISO93JIS62291984badd }
+    { JIS_C6229-1984-hand iso-ir-94 jp-ocr-hand csISO94JIS62291984hand }
+    { JIS_C6229-1984-hand-add iso-ir-95 jp-ocr-hand-add
+      csISO95JIS62291984handadd }
+    { JIS_C6229-1984-kana iso-ir-96 csISO96JISC62291984kana }
+    { ISO_2033-1983 iso-ir-98 e13b csISO2033 }
+    { ANSI_X3.110-1983 iso-ir-99 CSA_T500-1983 NAPLPS csISO99NAPLPS }
+    { ISO_8859-1:1987 iso-ir-100 ISO_8859-1 ISO-8859-1 latin1 l1 IBM819
+      CP819 csISOLatin1 }
+    { ISO_8859-2:1987 iso-ir-101 ISO_8859-2 ISO-8859-2 latin2 l2 csISOLatin2 }
+    { T.61-7bit iso-ir-102 csISO102T617bit }
+    { T.61-8bit T.61 iso-ir-103 csISO103T618bit }
+    { ISO_8859-3:1988 iso-ir-109 ISO_8859-3 ISO-8859-3 latin3 l3 csISOLatin3 }
+    { ISO_8859-4:1988 iso-ir-110 ISO_8859-4 ISO-8859-4 latin4 l4 csISOLatin4 }
+    { ECMA-cyrillic iso-ir-111 KOI8-E csISO111ECMACyrillic }
+    { CSA_Z243.4-1985-1 iso-ir-121 ISO646-CA csa7-1 ca csISO121Canadian1 }
+    { CSA_Z243.4-1985-2 iso-ir-122 ISO646-CA2 csa7-2 csISO122Canadian2 }
+    { CSA_Z243.4-1985-gr iso-ir-123 csISO123CSAZ24341985gr }
+    { ISO_8859-6:1987 iso-ir-127 ISO_8859-6 ISO-8859-6 ECMA-114 ASMO-708
+      arabic csISOLatinArabic }
+    { ISO_8859-6-E csISO88596E ISO-8859-6-E }
+    { ISO_8859-6-I csISO88596I ISO-8859-6-I }
+    { ISO_8859-7:1987 iso-ir-126 ISO_8859-7 ISO-8859-7 ELOT_928 ECMA-118
+      greek greek8 csISOLatinGreek }
+    { T.101-G2 iso-ir-128 csISO128T101G2 }
+    { ISO_8859-8:1988 iso-ir-138 ISO_8859-8 ISO-8859-8 hebrew
+      csISOLatinHebrew }
+    { ISO_8859-8-E csISO88598E ISO-8859-8-E }
+    { ISO_8859-8-I csISO88598I ISO-8859-8-I }
+    { CSN_369103 iso-ir-139 csISO139CSN369103 }
+    { JUS_I.B1.002 iso-ir-141 ISO646-YU js yu csISO141JUSIB1002 }
+    { ISO_6937-2-add iso-ir-142 csISOTextComm }
+    { IEC_P27-1 iso-ir-143 csISO143IECP271 }
+    { ISO_8859-5:1988 iso-ir-144 ISO_8859-5 ISO-8859-5 cyrillic
+      csISOLatinCyrillic }
+    { JUS_I.B1.003-serb iso-ir-146 serbian csISO146Serbian }
+    { JUS_I.B1.003-mac macedonian iso-ir-147 csISO147Macedonian }
+    { ISO_8859-9:1989 iso-ir-148 ISO_8859-9 ISO-8859-9 latin5 l5 csISOLatin5 }
+    { greek-ccitt iso-ir-150 csISO150 csISO150GreekCCITT }
+    { NC_NC00-10:81 cuba iso-ir-151 ISO646-CU csISO151Cuba }
+    { ISO_6937-2-25 iso-ir-152 csISO6937Add }
+    { GOST_19768-74 ST_SEV_358-88 iso-ir-153 csISO153GOST1976874 }
+    { ISO_8859-supp iso-ir-154 latin1-2-5 csISO8859Supp }
+    { ISO_10367-box iso-ir-155 csISO10367Box }
+    { ISO-8859-10 iso-ir-157 l6 ISO_8859-10:1992 csISOLatin6 latin6 }
+    { latin-lap lap iso-ir-158 csISO158Lap }
+    { JIS_X0212-1990 x0212 iso-ir-159 csISO159JISX02121990 }
+    { DS_2089 DS2089 ISO646-DK dk csISO646Danish }
+    { us-dk csUSDK }
+    { dk-us csDKUS }
+    { JIS_X0201 X0201 csHalfWidthKatakana }
+    { KSC5636 ISO646-KR csKSC5636 }
+    { ISO-10646-UCS-2 csUnicode }
+    { ISO-10646-UCS-4 csUCS4 }
+    { DEC-MCS dec csDECMCS }
+    { hp-roman8 roman8 r8 csHPRoman8 }
+    { macintosh mac csMacintosh }
+    { IBM037 cp037 ebcdic-cp-us ebcdic-cp-ca ebcdic-cp-wt ebcdic-cp-nl
+      csIBM037 }
+    { IBM038 EBCDIC-INT cp038 csIBM038 }
+    { IBM273 CP273 csIBM273 }
+    { IBM274 EBCDIC-BE CP274 csIBM274 }
+    { IBM275 EBCDIC-BR cp275 csIBM275 }
+    { IBM277 EBCDIC-CP-DK EBCDIC-CP-NO csIBM277 }
+    { IBM278 CP278 ebcdic-cp-fi ebcdic-cp-se csIBM278 }
+    { IBM280 CP280 ebcdic-cp-it csIBM280 }
+    { IBM281 EBCDIC-JP-E cp281 csIBM281 }
+    { IBM284 CP284 ebcdic-cp-es csIBM284 }
+    { IBM285 CP285 ebcdic-cp-gb csIBM285 }
+    { IBM290 cp290 EBCDIC-JP-kana csIBM290 }
+    { IBM297 cp297 ebcdic-cp-fr csIBM297 }
+    { IBM420 cp420 ebcdic-cp-ar1 csIBM420 }
+    { IBM423 cp423 ebcdic-cp-gr csIBM423 }
+    { IBM424 cp424 ebcdic-cp-he csIBM424 }
+    { IBM437 cp437 437 csPC8CodePage437 }
+    { IBM500 CP500 ebcdic-cp-be ebcdic-cp-ch csIBM500 }
+    { IBM775 cp775 csPC775Baltic }
+    { IBM850 cp850 850 csPC850Multilingual }
+    { IBM851 cp851 851 csIBM851 }
+    { IBM852 cp852 852 csPCp852 }
+    { IBM855 cp855 855 csIBM855 }
+    { IBM857 cp857 857 csIBM857 }
+    { IBM860 cp860 860 csIBM860 }
+    { IBM861 cp861 861 cp-is csIBM861 }
+    { IBM862 cp862 862 csPC862LatinHebrew }
+    { IBM863 cp863 863 csIBM863 }
+    { IBM864 cp864 csIBM864 }
+    { IBM865 cp865 865 csIBM865 }
+    { IBM866 cp866 866 csIBM866 }
+    { IBM868 CP868 cp-ar csIBM868 }
+    { IBM869 cp869 869 cp-gr csIBM869 }
+    { IBM870 CP870 ebcdic-cp-roece ebcdic-cp-yu csIBM870 }
+    { IBM871 CP871 ebcdic-cp-is csIBM871 }
+    { IBM880 cp880 EBCDIC-Cyrillic csIBM880 }
+    { IBM891 cp891 csIBM891 }
+    { IBM903 cp903 csIBM903 }
+    { IBM904 cp904 904 csIBBM904 }
+    { IBM905 CP905 ebcdic-cp-tr csIBM905 }
+    { IBM918 CP918 ebcdic-cp-ar2 csIBM918 }
+    { IBM1026 CP1026 csIBM1026 }
+    { EBCDIC-AT-DE csIBMEBCDICATDE }
+    { EBCDIC-AT-DE-A csEBCDICATDEA }
+    { EBCDIC-CA-FR csEBCDICCAFR }
+    { EBCDIC-DK-NO csEBCDICDKNO }
+    { EBCDIC-DK-NO-A csEBCDICDKNOA }
+    { EBCDIC-FI-SE csEBCDICFISE }
+    { EBCDIC-FI-SE-A csEBCDICFISEA }
+    { EBCDIC-FR csEBCDICFR }
+    { EBCDIC-IT csEBCDICIT }
+    { EBCDIC-PT csEBCDICPT }
+    { EBCDIC-ES csEBCDICES }
+    { EBCDIC-ES-A csEBCDICESA }
+    { EBCDIC-ES-S csEBCDICESS }
+    { EBCDIC-UK csEBCDICUK }
+    { EBCDIC-US csEBCDICUS }
+    { UNKNOWN-8BIT csUnknown8BiT }
+    { MNEMONIC csMnemonic }
+    { MNEM csMnem }
+    { VISCII csVISCII }
+    { VIQR csVIQR }
+    { KOI8-R csKOI8R }
+    { IBM00858 CCSID00858 CP00858 PC-Multilingual-850+euro }
+    { IBM00924 CCSID00924 CP00924 ebcdic-Latin9--euro }
+    { IBM01140 CCSID01140 CP01140 ebcdic-us-37+euro }
+    { IBM01141 CCSID01141 CP01141 ebcdic-de-273+euro }
+    { IBM01142 CCSID01142 CP01142 ebcdic-dk-277+euro ebcdic-no-277+euro }
+    { IBM01143 CCSID01143 CP01143 ebcdic-fi-278+euro ebcdic-se-278+euro }
+    { IBM01144 CCSID01144 CP01144 ebcdic-it-280+euro }
+    { IBM01145 CCSID01145 CP01145 ebcdic-es-284+euro }
+    { IBM01146 CCSID01146 CP01146 ebcdic-gb-285+euro }
+    { IBM01147 CCSID01147 CP01147 ebcdic-fr-297+euro }
+    { IBM01148 CCSID01148 CP01148 ebcdic-international-500+euro }
+    { IBM01149 CCSID01149 CP01149 ebcdic-is-871+euro }
+    { IBM1047 IBM-1047 }
+    { PTCP154 csPTCP154 PT154 CP154 Cyrillic-Asian }
+    { Amiga-1251 Ami1251 Amiga1251 Ami-1251 }
+    { UNICODE-1-1 csUnicode11 }
+    { CESU-8 csCESU-8 }
+    { BOCU-1 csBOCU-1 }
+    { UNICODE-1-1-UTF-7 csUnicode11UTF7 }
+    { ISO-8859-14 iso-ir-199 ISO_8859-14:1998 ISO_8859-14 latin8 iso-celtic
+      l8 }
+    { ISO-8859-15 ISO_8859-15 Latin-9 }
+    { ISO-8859-16 iso-ir-226 ISO_8859-16:2001 ISO_8859-16 latin10 l10 }
+    { GBK CP936 MS936 windows-936 }
+    { JIS_Encoding csJISEncoding }
+    { Shift_JIS MS_Kanji csShiftJIS }
+    { Extended_UNIX_Code_Packed_Format_for_Japanese csEUCPkdFmtJapanese
+      EUC-JP }
+    { Extended_UNIX_Code_Fixed_Width_for_Japanese csEUCFixWidJapanese }
+    { ISO-10646-UCS-Basic csUnicodeASCII }
+    { ISO-10646-Unicode-Latin1 csUnicodeLatin1 ISO-10646 }
+    { ISO-Unicode-IBM-1261 csUnicodeIBM1261 }
+    { ISO-Unicode-IBM-1268 csUnicodeIBM1268 }
+    { ISO-Unicode-IBM-1276 csUnicodeIBM1276 }
+    { ISO-Unicode-IBM-1264 csUnicodeIBM1264 }
+    { ISO-Unicode-IBM-1265 csUnicodeIBM1265 }
+    { ISO-8859-1-Windows-3.0-Latin-1 csWindows30Latin1 }
+    { ISO-8859-1-Windows-3.1-Latin-1 csWindows31Latin1 }
+    { ISO-8859-2-Windows-Latin-2 csWindows31Latin2 }
+    { ISO-8859-9-Windows-Latin-5 csWindows31Latin5 }
+    { Adobe-Standard-Encoding csAdobeStandardEncoding }
+    { Ventura-US csVenturaUS }
+    { Ventura-International csVenturaInternational }
+    { PC8-Danish-Norwegian csPC8DanishNorwegian }
+    { PC8-Turkish csPC8Turkish }
+    { IBM-Symbols csIBMSymbols }
+    { IBM-Thai csIBMThai }
+    { HP-Legal csHPLegal }
+    { HP-Pi-font csHPPiFont }
+    { HP-Math8 csHPMath8 }
+    { Adobe-Symbol-Encoding csHPPSMath }
+    { HP-DeskTop csHPDesktop }
+    { Ventura-Math csVenturaMath }
+    { Microsoft-Publishing csMicrosoftPublishing }
+    { Windows-31J csWindows31J }
+    { GB2312 csGB2312 }
+    { Big5 csBig5 }
+}
+
+proc tcl_encoding {enc} {
+    global encoding_aliases
+    set names [encoding names]
+    set lcnames [string tolower $names]
+    set enc [string tolower $enc]
+    set i [lsearch -exact $lcnames $enc]
+    if {$i < 0} {
+       # look for "isonnn" instead of "iso-nnn" or "iso_nnn"
+       if {[regsub {^iso[-_]} $enc iso encx]} {
+           set i [lsearch -exact $lcnames $encx]
+       }
+    }
+    if {$i < 0} {
+       foreach l $encoding_aliases {
+           set ll [string tolower $l]
+           if {[lsearch -exact $ll $enc] < 0} continue
+           # look through the aliases for one that tcl knows about
+           foreach e $ll {
+               set i [lsearch -exact $lcnames $e]
+               if {$i < 0} {
+                   if {[regsub {^iso[-_]} $e iso ex]} {
+                       set i [lsearch -exact $lcnames $ex]
+                   }
+               }
+               if {$i >= 0} break
+           }
+           break
+       }
+    }
+    if {$i >= 0} {
+       return [lindex $names $i]
+    }
+    return {}
+}
+
 # defaults...
 set datemode 0
 set diffopts "-U 5 -p"
 set wrcomcmd "git-diff-tree --stdin -p --pretty"
 
-set gitencoding ""
+set gitencoding {}
 catch {
     set gitencoding [exec git-repo-config --get i18n.commitencoding]
 }
 if {$gitencoding == ""} {
-       set gitencoding "utf-8"
+    set gitencoding "utf-8"
+}
+set tclencoding [tcl_encoding $gitencoding]
+if {$tclencoding == {}} {
+    puts stderr "Warning: encoding $gitencoding is not supported by Tcl/Tk"
 }
 
 set mainfont {Helvetica 9}