Move the `_which` function (almost) to the top

We are about to make use of the `_which` function to address
CVE-2022-41953 by overriding Tcl/Tk's unsafe PATH lookup on Windows.

In preparation for that, let's move it close to the top of the file to
make sure that even early `exec` calls that happen during the start-up
of Git GUI benefit from the fix.

This commit is best viewed with `--color-moved`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Pratyush Yadav <me@yadavpratyush.com>

diff --git a/git-gui.sh b/git-gui.sh
index f779fc92684856134629a41a3789db4b6ab7d890..b0eb5a6ae48c00b73994fdb9d418aba3a6c806dd 100755 (executable)
--- a/git-gui.sh
+++ b/git-gui.sh
@@ -75,6 +75,52 @@ proc is_Cygwin {} {
        return $_iscygwin
 }
 
+######################################################################
+##
+## PATH lookup
+
+set _search_path {}
+proc _which {what args} {
+       global env _search_exe _search_path
+
+       if {$_search_path eq {}} {
+               if {[is_Cygwin] && [regexp {^(/|\.:)} $env(PATH)]} {
+                       set _search_path [split [exec cygpath \
+                               --windows \
+                               --path \
+                               --absolute \
+                               $env(PATH)] {;}]
+                       set _search_exe .exe
+               } elseif {[is_Windows]} {
+                       set gitguidir [file dirname [info script]]
+                       regsub -all ";" $gitguidir "\\;" gitguidir
+                       set env(PATH) "$gitguidir;$env(PATH)"
+                       set _search_path [split $env(PATH) {;}]
+                       # Skip empty `PATH` elements
+                       set _search_path [lsearch -all -inline -not -exact \
+                               $_search_path ""]
+                       set _search_exe .exe
+               } else {
+                       set _search_path [split $env(PATH) :]
+                       set _search_exe {}
+               }
+       }
+
+       if {[is_Windows] && [lsearch -exact $args -script] >= 0} {
+               set suffix {}
+       } else {
+               set suffix $_search_exe
+       }
+
+       foreach p $_search_path {
+               set p [file join $p $what$suffix]
+               if {[file exists $p]} {
+                       return [file normalize $p]
+               }
+       }
+       return {}
+}
+
 ######################################################################
 ##
 ## locate our library
@@ -194,7 +240,6 @@ set _isbare {}
 set _gitexec {}
 set _githtmldir {}
 set _reponame {}
-set _search_path {}
 set _shellpath {@@SHELL_PATH@@}
 
 set _trace [lsearch -exact $argv --trace]
@@ -444,47 +489,6 @@ proc _git_cmd {name} {
        return $v
 }
 
-proc _which {what args} {
-       global env _search_exe _search_path
-
-       if {$_search_path eq {}} {
-               if {[is_Cygwin] && [regexp {^(/|\.:)} $env(PATH)]} {
-                       set _search_path [split [exec cygpath \
-                               --windows \
-                               --path \
-                               --absolute \
-                               $env(PATH)] {;}]
-                       set _search_exe .exe
-               } elseif {[is_Windows]} {
-                       set gitguidir [file dirname [info script]]
-                       regsub -all ";" $gitguidir "\\;" gitguidir
-                       set env(PATH) "$gitguidir;$env(PATH)"
-                       set _search_path [split $env(PATH) {;}]
-                       # Skip empty `PATH` elements
-                       set _search_path [lsearch -all -inline -not -exact \
-                               $_search_path ""]
-                       set _search_exe .exe
-               } else {
-                       set _search_path [split $env(PATH) :]
-                       set _search_exe {}
-               }
-       }
-
-       if {[is_Windows] && [lsearch -exact $args -script] >= 0} {
-               set suffix {}
-       } else {
-               set suffix $_search_exe
-       }
-
-       foreach p $_search_path {
-               set p [file join $p $what$suffix]
-               if {[file exists $p]} {
-                       return [file normalize $p]
-               }
-       }
-       return {}
-}
-
 # Test a file for a hashbang to identify executable scripts on Windows.
 proc is_shellscript {filename} {
        if {![file exists $filename]} {return 0}