extdiff: avoid unexpected quoting arguments for external tools (issue4463) Before this patch, all command line arguments for external tools are quoted by the combination of "shlex.split" and "util.shellquote". But this causes some problems. - some problematic commands can't work correctly with quoted arguments For example, 'WinMerge /r ....' is OK, but 'WinMerge "/r" ....' is NG. See also below for detail about this problem. https://bitbucket.org/tortoisehg/thg/issue/3978/ - quoting itself may change semantics of arguments For example, when the environment variable CONCAT="foo bar baz': - mydiff $CONCAT => mydiff foo bar baz (taking 3 arguments) - mydiff "$CONCAT" => mydiff "foo bar baz" (taking only 1 argument) For another example, single quoting (= "util.shellquote") on POSIX environment prevents shells from expanding environment variables, tilde, and so on: - mydiff "$HOME" => mydiff /home/foobar - mydiff '$HOME' => mydiff $HOME - "shlex.split" can't handle some special characters correctly It just splits specified command line by whitespaces. For example, "echo foo;echo bar" is split into ["echo", "foo;echo", "bar"]. On the other hand, if quoting itself is omitted, users can't specify options including space characters with "--option" at runtime. The root cause of this issue is that "shlex.split + util.shellquote" combination loses whether users really want to quote each command line elements or not, even though these can be quoted arbitrarily in configurations. To resolve this problem, this patch does: - prevent configurations from being processed by "shlex.split" and "util.shellquote" only (possibly) "findexe"-ed or "findexternaltool"-ed command path is "util.shellquote", because it may contain whitespaces. - quote options specified by "--option" via command line at runtime This patch also makes "dodiff()" take only one "args" argument instead of "diffcmd" and "diffopts. It also omits applying "util.shellquote" on "args", because "args" should be already stringified in "extdiff()" and "mydiff()". The last hunk for "test-extdiff.t" replaces two whitespaces by single whitespace, because change of "' '.join()" logic causes omitting redundant whitespaces.