git-gui: Implement basic branch switching through read-tree.

If the user selects a different branch from the Branch menu, or asks
us to create a new branch and immediately checkout that branch we
now perform the update of the working directory by way of a 2 way
read-tree invocation.

This emulates the behavior of `git checkout branch` or the behavior
of `git checkout -b branch initrev`.  We don't however support the
-m style behavior, where a switch can occur with file level merging
performed by merge-recursive.  Support for this is planned for a
future update.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

diff --git a/git-gui.sh b/git-gui.sh
index 5171db6f278854e60f8473b25cd7acbd58eb024a..b5c2c7406d2d09d7d52a2c3fd25d79cec64fa48f 100755 (executable)
--- a/git-gui.sh
+++ b/git-gui.sh
@@ -2155,16 +2155,11 @@ proc do_delete_branch {} {
        tkwait window $w
 }
 
-proc switch_branch {b} {
-       global HEAD commit_type file_states current_branch
-       global selected_commit_type ui_comm
+proc switch_branch {new_branch} {
+       global HEAD commit_type current_branch repo_config
 
        if {![lock_index switch]} return
 
-       # -- Backup the selected branch (repository_state resets it)
-       #
-       set new_branch $current_branch
-
        # -- Our in memory state should match the repository.
        #
        repository_state curType curHEAD curMERGE_HEAD
@@ -2185,19 +2180,110 @@ The rescan will be automatically started now.
                return
        }
 
-       # -- Toss the message buffer if we are in amend mode.
+       if {$repo_config(gui.trustmtime) eq {true}} {
+               switch_branch_stage2 {} $new_branch
+       } else {
+               set ui_status_value {Refreshing file status...}
+               set cmd [list git update-index]
+               lappend cmd -q
+               lappend cmd --unmerged
+               lappend cmd --ignore-missing
+               lappend cmd --refresh
+               set fd_rf [open "| $cmd" r]
+               fconfigure $fd_rf -blocking 0 -translation binary
+               fileevent $fd_rf readable \
+                       [list switch_branch_stage2 $fd_rf $new_branch]
+       }
+}
+
+proc switch_branch_stage2 {fd_rf new_branch} {
+       global ui_status_value HEAD
+
+       if {$fd_rf ne {}} {
+               read $fd_rf
+               if {![eof $fd_rf]} return
+               close $fd_rf
+       }
+
+       set ui_status_value "Updating working directory to '$new_branch'..."
+       set cmd [list git read-tree]
+       lappend cmd -m
+       lappend cmd -u
+       lappend cmd --exclude-per-directory=.gitignore
+       lappend cmd $HEAD
+       lappend cmd $new_branch
+       set fd_rt [open "| $cmd" r]
+       fconfigure $fd_rt -blocking 0 -translation binary
+       fileevent $fd_rt readable \
+               [list switch_branch_readtree_wait $fd_rt $new_branch]
+}
+
+proc switch_branch_readtree_wait {fd_rt new_branch} {
+       global selected_commit_type commit_type HEAD MERGE_HEAD PARENT
+       global current_branch
+       global ui_comm ui_status_value
+
+       # -- We never get interesting output on stdout; only stderr.
        #
-       if {[string match amend* $curType]} {
-               $ui_comm delete 0.0 end
-               $ui_comm edit reset
-               $ui_comm edit modified false
+       read $fd_rt
+       fconfigure $fd_rt -blocking 1
+       if {![eof $fd_rt]} {
+               fconfigure $fd_rt -blocking 0
+               return
        }
 
-       set selected_commit_type new
-       set current_branch $new_branch
+       # -- The working directory wasn't in sync with the index and
+       #    we'd have to overwrite something to make the switch. A
+       #    merge is required.
+       #
+       if {[catch {close $fd_rt} err]} {
+               regsub {^fatal: } $err {} err
+               warn_popup "File level merge required.
+
+$err
+
+Staying on branch '$current_branch'."
+               set ui_status_value "Aborted checkout of '$new_branch' (file level merging is required)."
+               unlock_index
+               return
+       }
+
+       # -- Update the symbolic ref.  Core git doesn't even check for failure
+       #    here, it Just Works(tm).  If it doesn't we are in some really ugly
+       #    state that is difficult to recover from within git-gui.
+       #
+       if {[catch {exec git symbolic-ref HEAD "refs/heads/$new_branch"} err]} {
+               error_popup "Failed to set current branch.
+
+This working directory is only partially switched.
+We successfully updated your files, but failed to
+update an internal Git file.
+
+This should not have occurred.  [appname] will now
+close and give up.
 
+$err"
+               do_quit
+               return
+       }
+
+       # -- Update our repository state.  If we were previously in amend mode
+       #    we need to toss the current buffer and do a full rescan to update
+       #    our file lists.  If we weren't in amend mode our file lists are
+       #    accurate and we can avoid the rescan.
+       #
        unlock_index
-       error "NOT FINISHED"
+       set selected_commit_type new
+       if {[string match amend* $commit_type]} {
+               $ui_comm delete 0.0 end
+               $ui_comm edit reset
+               $ui_comm edit modified false
+               rescan {set ui_status_value "Checked out branch '$current_branch'."}
+       } else {
+               repository_state commit_type HEAD MERGE_HEAD
+               set PARENT $HEAD
+               set ui_status_value "Checked out branch '$current_branch'."
+       }
 }
 
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