Git auto completion does not work for comparing 2 files from 2 different branches

Git auto completion does not work for comparing 2 files from 2 different branches

[한현빈]

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I compare 2 different files from git remote like this:
git diff origin/branch1:file.txt origin/branch2:file.txt
However, auto completion only works until this point: git diff origin/branch1:file.txt, pressing tab afterward does not bring me list of usable remotes, branches in the said remote, and files in the said branch, unlike first one in branch1, which auto completion works fine.
 
Steps to reproduce

Clone any repository with 2 or more branches
Try to get difference of 2 files using git diff origin/branch1:path/to/file origin/branch2:path/to/file
Observe that auto completion doesn't work for second one

OS is KDE Neon, 20.04
Terminal I used is Yakuake and Konsole
ZSH version is 5.8

I have attached video of me reproducing the issue.

From Hyun Bin, and thank you for your effort on this.

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Re: Git auto completion does not work for comparing 2 files from 2 different branches

[Bart Schaefer]

On Thu, Sep 29, 2022 at 9:17 PM 한현빈 <ironman466@naver.com> wrote:
>
> However, auto completion only works until this point: git diff origin/branch1:file.txt, pressing tab afterward does not bring me list of usable remotes, branches in the said remote, and files in the said branch, unlike first one in branch1, which auto completion works fine.

Confirmed this is still the case in 5.9 -- git diff completion always
assumes you're comparing a branch to the current checkout.

[PATCH] Re: Git auto completion does not work for comparing 2 files from 2 different branches

[Bart Schaefer]

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On Fri, Sep 30, 2022 at 5:54 PM Bart Schaefer <schaefer@brasslantern.com> wrote:
>
> Confirmed this is still the case in 5.9 -- git diff completion always
> assumes you're comparing a branch to the current checkout.

Any reason not to rearrange like so?

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diff --git a/Completion/Unix/Command/_git b/Completion/Unix/Command/_git
index cecb80ac3..6a1c4158a 100644
--- a/Completion/Unix/Command/_git
+++ b/Completion/Unix/Command/_git
@@ -808,18 +808,6 @@ _git-diff () {
 
       # Otherwise, more complex conditions need to be checked.
       case $CURRENT in
-        (1)
-          local files_alt='files::__git_changed-in-working-tree_files'
-          if [[ -n ${opt_args[(I)--cached|--staged]} ]]; then
-            files_alt='files::__git_changed-in-index_files'
-          fi
-
-          _alternative \
-            'commit-ranges::__git_commit_ranges' \
-            'blobs-and-trees-in-treeish::__git_blobs_and_trees_in_treeish' \
-            $files_alt \
-            'blobs::__git_blobs ' && ret=0
-          ;;
         (2)
           # Check if first argument is something special. In case of committish ranges and committishs offer a full list compatible completions.
           if __git_is_committish_range $line[1]; then
@@ -841,10 +829,19 @@ _git-diff () {
           elif [[ -n ${opt_args[(I)--cached|--staged]} ]]; then
             # Example: git diff --cached file1 <tab>
             __git_changed-in-index_files && ret=0
-          else
-            # Example: git diff file1 <tab>
-            __git_changed-in-working-tree_files && ret=0
           fi
+          ;&
+        (1)
+          local files_alt='files::__git_changed-in-working-tree_files'
+          if [[ -n ${opt_args[(I)--cached|--staged]} ]]; then
+            files_alt='files::__git_changed-in-index_files'
+          fi
+
+          _alternative \
+            'commit-ranges::__git_commit_ranges' \
+            'blobs-and-trees-in-treeish::__git_blobs_and_trees_in_treeish' \
+            $files_alt \
+            'blobs::__git_blobs ' && ret=0
           ;;
         (*)
           if __git_is_committish_range $line[1]; then