@matheusbsbs / matheus-bagliano / commits / aa1b8d31ac

gitk: use -profile tcl8 for file input with Tcl 9

gitk invokes many git commands expecting output in utf-8 encoding, but git accepts extended ascii (code page unknown) as utf-8 without validating, so cannot guarantee valid utf-8 on output. In particular, using any extended ascii code page, of which there are many, has long been acceptable given that everyone on a project is aware of and uses that same code page to view all data. utf-8 accepts only 7-bit ascii characters in single bytes, and any characters outside of that base set require at least two bytes. Tcl is a string based language, and transcodes all input data to an internal unicode format, and to whatever format is requested on output: "pure" binary is recoded using iso8859-1. Tcl8.x silently recodes invalid utf-8 as binary data, so extended ascii characters maintain their binary value on output but may not display correctly. Tcl 8.7 added three profiles to control this behaviour: strict (raises exceptions), replace (replaces each invalid byte with ?), and the default tcl8 maintaining the old behavior. Tcl 9 changes the default profile to strict, meaning any invalid utf-8 raises an exception that gitk does not handle. An example of this in the git repository is commit 7eb93c8965 ("[PATCH] Simplify git script", 2005-09-07). This includes extended ascii characters in the author name and commit message. As a result, gitk + Tcl 9 cannot view the git repository at any point beyond that commit. Note: Tcl 9.0 has a bug, to be fixed in 9.1, where this particular condition results in a memory error causing Tcl to crash [1]. The tcl8 profile used so far has acceptable behavior given gitk's acceptance: this allows gitk to accept extended ascii though it may display incorrectly. Let's continue that behavior by overriding open to use the tcl8 profile on Tcl9 and later: Tcl 8.6 does not understand fconfigure -profile, and Tcl 8.7 maintains the tcl8 profile. [1] Per https://core.tcl-lang.org/tcl/tktview/73bb42fb3f35cd613af6fcea465e35bbfd352216 Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>

Mark Levedahl committed Mar 14, 2025 at 11:45 UTC aa1b8d31acbcc7630e1ca2f2bbd27eeb34b00446
1 file changed +13
gitk
+13
@@ -33,6 +33,19 @@ The version of git found is $git_version."
33 exit 1
34 }
35
36 +######################################################################
37 +## Enable Tcl8 profile in Tcl9, allowing consumption of data that has
38 +## bytes not conforming to the assumed encoding profile.
39 +
40 +if {[package vcompare $::tcl_version 9.0] >= 0} {
41 + rename open _strict_open
42 + proc open args {
43 + set f [_strict_open {*}$args]
44 + chan configure $f -profile tcl8
45 + return $f
46 + }
47 +}
48 +
49 ######################################################################
50 ##
51 ## Enabling platform-specific code paths