[PATCH v4] vcs_info: choose backend by basedir

[Aleksandr Mezin <mezin.alexander@xxxxxxxxx>]

Previously, vcs_info iterated over enabled VCS backends and output repository
status from the first backend that works (i.e. first backend that can find a
repository).

But I prefer a different behavior: I want to see the status of the repository
closest to the current working directory. For example: if there is a Mercurial
repository inside a Git repository, and I 'cd' into the Mercurial repository,
I want to see the status of Mercurial repo, even if 'git' comes before 'hg' in
the 'enable' list.

This patch adds a new algorithm for vcs_info to choose the backend:

1. Among backends whose basedir isn't an ancestor of the current directory,
old algorithm is used: whichever comes first in 'enable' list.

2. If all backends return basedirs that are ancestors of the current directory,
the one with basedir closest to the current directory is chosen.

As far as I know, unless the user has set basedir manually (GIT_WORK_TREE),
all backend return basedirs that are ancestors of the current directory.
Backends that return non-ancestor basedirs have higher priority to show the
status of that manually-configured repository.

The algorithm used by vcs_info can be configured using 'choose-closest-backend'
zstyle:

    zstyle ':vcs_info:*' choose-closest-backend yes

By default, old algorithm is used.

It can also be configured per-backend:

    zstyle ':vcs_info:hg:*' choose-closest-backend no

This effectively moves the backend into group (1), as if its basedir is never
an ancestor of the current directory. Not sure how useful this is though.

Also, this patch adjusts VCS_INFO_detect_git and VCS_INFO_detect_cvs to make
them set vcs_comm[basedir], by moving basedir detection code from corresponding
VCS_INFO_get_data_* functions. VCS_INFO_detect_git and VCS_INFO_detect_cvs were
the only VCS_INFO_detect_* functions not setting it.

Signed-off-by: Aleksandr Mezin <mezin.alexander@xxxxxxxxx>
---
v4: back to boolean zstyle, keep old behavior by default, documentation

 Completion/Zsh/Command/_zstyle                |  1 +
 Doc/Zsh/contrib.yo                            | 41 +++++++++++++++++++
 .../VCS_Info/Backends/VCS_INFO_detect_cvs     | 17 +++++++-
 .../VCS_Info/Backends/VCS_INFO_detect_git     |  1 +
 .../VCS_Info/Backends/VCS_INFO_get_data_cvs   | 11 +----
 .../VCS_Info/Backends/VCS_INFO_get_data_git   |  2 +-
 Functions/VCS_Info/vcs_info                   | 30 ++++++++++++--
 7 files changed, 86 insertions(+), 17 deletions(-)

diff --git a/Completion/Zsh/Command/_zstyle b/Completion/Zsh/Command/_zstyle
index 75acde5f7..e094b3da8 100644
--- a/Completion/Zsh/Command/_zstyle
+++ b/Completion/Zsh/Command/_zstyle
@@ -192,6 +192,7 @@ styles=(
   quilt-standalone       v:bool
   quilt-patch-dir        v:_directories
   quiltcommand           v:_command_names
+  choose-closest-backend v:bool
 
   chpwd			 z:bool
   progress		 z:progress
diff --git a/Doc/Zsh/contrib.yo b/Doc/Zsh/contrib.yo
index 00f693664..c0b730850 100644
--- a/Doc/Zsh/contrib.yo
+++ b/Doc/Zsh/contrib.yo
@@ -1238,6 +1238,46 @@ of unapplied patches (for example with Mercurial Queue patches).
 
 Used by the tt(quilt), tt(hg), and tt(git) backends.
 )
+kindex(choose-closest-backend)
+item(tt(choose-closest-backend))(
+By default, tt(vcs_info) tries backends in the order given by the tt(enable)
+style, and operates on the repository detected by the first backend to
+successfully detect a repository.
+
+If this style (tt(choose-closest-backend)) is set to tt(true) for some (or all)
+backends, all backends will be divided into two groups:
+
+1) Backends, for which this style is set to tt(true), that detect a
+repository/working copy that is an ancestor of the current directory (including
+the current directory itself).
+
+2) All other backends: backends with tt(choose-closest-backend) unset/set to
+tt(false); and backends that detected a repository/working copy that's not an
+ancestor of the current directory, even if tt(choose-closest-backend) is set to
+tt(true) for them.
+
+First, tt(vcs_info) will try backends from the 2nd group in the order given by
+the tt(enable) style, and operate on the repository detected by the first
+backend to successfully detect a repository (the default behavior of
+tt(vcs_info), only limited to backends from the 2nd group).
+
+If no backends from the 2nd group detected a repository (or if there are no
+backends in that group), tt(vcs_info) will try backends from the 1st group.
+tt(vcs_info) will then operate on the repository closest to the current working
+directory.
+
+Usually, all VCS backends search for repositories only in ancestors of the
+current directory, and choose the repository closest to the current directory.
+So if tt(choose-closest-backend) is set to tt(true) globally for all backends,
+tt(vcs_info) will effectively search for the repository closest to the current
+directory.
+
+However, there is at least one backend that can detect a repository in an
+arbitrary location - Git backend. tt(GIT_WORK_TREE) can be set to a path that
+doesn't point to an ancestor of the current directory. In this case, even if
+tt(choose-closest-backend) is set to tt(true) globally for all backends,
+the repository/working copy pointed by tt(GIT_WORK_TREE) will be preferred.
+)
 enditem()
 
 The default values for these styles in all contexts are:
@@ -1272,6 +1312,7 @@ sitem(tt(quiltcommand))(quilt)
 sitem(tt(patch-format))(var(backend dependent))
 sitem(tt(nopatch-format))(var(backend dependent))
 sitem(tt(get-unapplied))(false)
+sitem(tt(choose-closest-backend))(false)
 endsitem()
 
 In normal tt(formats) and tt(actionformats) the following replacements are
diff --git a/Functions/VCS_Info/Backends/VCS_INFO_detect_cvs b/Functions/VCS_Info/Backends/VCS_INFO_detect_cvs
index 7a5ee1eef..a57959ec9 100644
--- a/Functions/VCS_Info/Backends/VCS_INFO_detect_cvs
+++ b/Functions/VCS_Info/Backends/VCS_INFO_detect_cvs
@@ -7,5 +7,18 @@ setopt localoptions NO_shwordsplit
 [[ $1 == '--flavours' ]] && return 1
 
 VCS_INFO_check_com ${vcs_comm[cmd]} || return 1
-[[ -d "./CVS" ]] && [[ -r "./CVS/Repository" ]] && return 0
-return 1
+if ! [[ -d "./CVS" ]] || ! [[ -r "./CVS/Repository" ]] ; then
+    return 1
+fi
+
+# Look for the most distant parent that still has a CVS subdirectory.
+local cvsbase="."
+cvsbase=${cvsbase:P}
+while [[ -d "${cvsbase:h}/CVS" ]]; do
+    cvsbase="${cvsbase:h}"
+    if [[ $cvsbase == '/' ]]; then
+        break
+    fi
+done
+
+vcs_comm[basedir]="${cvsbase}"
diff --git a/Functions/VCS_Info/Backends/VCS_INFO_detect_git b/Functions/VCS_Info/Backends/VCS_INFO_detect_git
index e4191f474..b7955de38 100644
--- a/Functions/VCS_Info/Backends/VCS_INFO_detect_git
+++ b/Functions/VCS_Info/Backends/VCS_INFO_detect_git
@@ -7,6 +7,7 @@ setopt localoptions NO_shwordsplit
 [[ $1 == '--flavours' ]] && { print -l git-p4 git-svn; return 0 }
 
 if VCS_INFO_check_com ${vcs_comm[cmd]} && vcs_comm[gitdir]="$(${vcs_comm[cmd]} rev-parse --git-dir 2> /dev/null)" ; then
+    vcs_comm[basedir]="$( ${vcs_comm[cmd]} rev-parse --show-toplevel 2> /dev/null )"
     if   [[ -d ${vcs_comm[gitdir]}/svn ]]             ; then vcs_comm[overwrite_name]='git-svn'
     elif [[ -d ${vcs_comm[gitdir]}/refs/remotes/p4 ]] ; then vcs_comm[overwrite_name]='git-p4' ; fi
     return 0
diff --git a/Functions/VCS_Info/Backends/VCS_INFO_get_data_cvs b/Functions/VCS_Info/Backends/VCS_INFO_get_data_cvs
index 9b828bd11..bc0d5cfe5 100644
--- a/Functions/VCS_Info/Backends/VCS_INFO_get_data_cvs
+++ b/Functions/VCS_Info/Backends/VCS_INFO_get_data_cvs
@@ -5,17 +5,8 @@
 setopt localoptions NO_shwordsplit
 local cvsbranch cvsbase
 
-# Look for the most distant parent that still has a CVS subdirectory.
+cvsbase="${vcs_comm[basedir]}"
 # VCS_INFO_detect_cvs ensured that ./CVS/Repository exists.
-cvsbase="."
-cvsbase=${cvsbase:P}
-while [[ -d "${cvsbase:h}/CVS" ]]; do
-    cvsbase="${cvsbase:h}"
-    if [[ $cvsbase == '/' ]]; then
-        break
-    fi
-done
-
 cvsbranch=$(< ./CVS/Repository)
 rrn=${cvsbase:t}
 cvsbranch=${cvsbranch##${rrn}/}
diff --git a/Functions/VCS_Info/Backends/VCS_INFO_get_data_git b/Functions/VCS_Info/Backends/VCS_INFO_get_data_git
index 79429c8e0..eb04d4b41 100644
--- a/Functions/VCS_Info/Backends/VCS_INFO_get_data_git
+++ b/Functions/VCS_Info/Backends/VCS_INFO_get_data_git
@@ -138,7 +138,7 @@ VCS_INFO_git_handle_patches () {
 
 gitdir=${vcs_comm[gitdir]}
 VCS_INFO_git_getbranch ${gitdir}
-gitbase=$( ${vcs_comm[cmd]} rev-parse --show-toplevel 2> /dev/null )
+gitbase=${vcs_comm[basedir]}
 if [[ -z ${gitbase} ]]; then
     # Bare repository
     gitbase=${gitdir:P}
diff --git a/Functions/VCS_Info/vcs_info b/Functions/VCS_Info/vcs_info
index 786b61918..0769bc877 100644
--- a/Functions/VCS_Info/vcs_info
+++ b/Functions/VCS_Info/vcs_info
@@ -54,7 +54,7 @@ vcs_info () {
     [[ -r . ]] || return 0
 
     local pat
-    local -i found retval
+    local -i retval
     local -a enabled disabled dps
     local usercontext vcs rrn quiltmode
     local -x LC_MESSAGES
@@ -114,7 +114,9 @@ vcs_info () {
 
     VCS_INFO_maxexports
 
-    (( found = 0 ))
+    local -A chosen_vcs_comm chosen_backend_misc
+    local chosen_vcs basedir_realpath chosen_basedir_realpath choose_first_available
+
     for vcs in ${enabled} ; do
         [[ -n ${(M)disabled:#${vcs}} ]] && continue
         if (( ${+functions[VCS_INFO_detect_${vcs}]} == 0 )) ; then
@@ -124,10 +126,30 @@ vcs_info () {
         fi
         vcs_comm=()
         VCS_INFO_get_cmd
-        VCS_INFO_detect_${vcs} && (( found = 1 )) && break
+        if VCS_INFO_detect_${vcs}; then
+            basedir_realpath="${vcs_comm[basedir]:P}"
+
+            zstyle -t ":vcs_info:${vcs}:${usercontext}:${rrn}" choose-closest-backend
+            choose_first_available=$?
+
+            [[ "${PWD:P}/" == "${basedir_realpath}"/* ]] || choose_first_available=1
+
+            if (( choose_first_available )) || (( ${#basedir_realpath} > ${#chosen_basedir_realpath} )) ; then
+                chosen_vcs="${vcs}"
+                chosen_vcs_comm=("${(kv)vcs_comm[@]}")
+                chosen_backend_misc=("${(kv)backend_misc[@]}")
+                chosen_basedir_realpath="${basedir_realpath}"
+
+                (( choose_first_available )) && break
+            fi
+        fi
     done
 
-    (( found == 0 )) && {
+    vcs="${chosen_vcs}"
+    vcs_comm=("${(kv)chosen_vcs_comm[@]}")
+    backend_misc=("${(kv)chosen_backend_misc[@]}")
+
+    [ -z "${vcs}" ] && {
         vcs='-quilt-'; quiltmode='standalone'
         VCS_INFO_quilt standalone || VCS_INFO_set --nvcs
         return 0
-- 
2.29.2