completion: repair config completion for Zsh

Commit 1e0ee4087e (completion: add and use __git_compute_first_level_config_vars_for_section, 2024-02-10) uses an indirect variable syntax that is only valid for Bash, but the Zsh completion code relies on the Bash completion code to function. Zsh supports a different indirect variable expansion using ${(P)var}, but in `emulate ksh` mode does not support Bash's ${!var}. This manifests as completing strange config options like "__git_first_level_config_vars_for_section_remote" as a choice for the command line git config set remote. Using Zsh's C-x ? _complete_debug widget with the cursor at the end of that command line captures a trace, in which we see (some details elided): +__git_complete_config_variable_name:7> __git_compute_first_level_config_vars_for_section remote +__git_compute_first_level_config_vars_for_section:7> local section=remote +__git_compute_first_level_config_vars_for_section:7> __git_compute_config_vars +__git_compute_config_vars:7> test -n $'add.ignoreErrors\nadvice.addEmbeddedRepo\nadvice.addEmptyPathspec\nadvice.addIgnoredFile[…]' +__git_compute_first_level_config_vars_for_section:7> local this_section=__git_first_level_config_vars_for_section_remote +__git_compute_first_level_config_vars_for_section:7> test -n __git_first_level_config_vars_for_section_remote +__git_complete_config_variable_name:7> local this_section=__git_first_level_config_vars_for_section_remote +__git_complete_config_variable_name:7> __gitcomp_nl_append __git_first_level_config_vars_for_section_remote remote. '' ' ' +__gitcomp_nl_append:7> __gitcomp_nl __git_first_level_config_vars_for_section_remote remote. '' ' ' +__gitcomp_nl:7> emulate -L zsh +__gitcomp_nl:7> compset -P '*[=:]' +__gitcomp_nl:7> compadd -Q -S ' ' -p remote. -- __git_first_level_config_vars_for_section_remote We perform the test for __git_compute_config_vars correctly, but the ${!this_section} references are not expanded as expected. Instead, portably expand indirect references through the new __git_indirect. Contrary to some versions you might find online [1], this version avoids echo non-portabilities [2] [3] and correctly quotes the indirect expansion after eval (so that the result is not split or globbed before being handed to printf). [1]: https://unix.stackexchange.com/a/41409/301073 [2]: https://askubuntu.com/questions/715765/mysterious-behavior-of-echo-command#comment1056038_715769 [3]: https://mywiki.wooledge.org/CatEchoLs The following demo program demonstrates how this works: b=1 indirect() { eval printf '%s' "\"\$$1\"" } f() { # Comment this out to see that it works for globals, too. Or, use # a value with spaces like '2 3 4' to see how it handles those. local b=2 local a=b test -n "$(indirect $a)" && echo nice } f When placed in a file "demo", then both bash -x demo and zsh -xc 'emulate ksh -c ". ./demo"' |& tail provide traces showing that "$(indirect $a)" produces 2 (or 1, with the global, or "2 3 4" as a single string, etc.). Signed-off-by: D. Ben Knoble <ben.knoble+github@gmail.com> Acked-by: Philippe Blain <levraiphilippeblain@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>