Refactor: Replace deferred code in enter commands with functions

In _forgit_log and _forgit_enter it is possible to diff a single
commit/file by pressing enter. We used to store the code that executes
the diffs in variables and passed it to fzf as deferred code. This
refactor reduces the amount of deferred code by using functions instead
of variables.

bin/git-forgit

@@ -115,16 +115,22 @@ _forgit_log_preview() {
     echo "$sha" | xargs -I% git show --color=always -U"$_forgit_preview_context" % -- "$@" | $_forgit_show_pager
 }
 
+_forgit_log_enter() {
+    local sha
+    sha=$(echo "$1" | _forgit_extract_sha)
+    shift
+    echo "$sha" | xargs -I% "${FORGIT}" diff %^! "$@"
+}
+
 # git commit viewer
 _forgit_log() {
     _forgit_inside_work_tree || return 1
-    local opts graph files log_format enter_cmd
+    local opts graph files log_format
     files=$(sed -nE 's/.*-- (.*)/\1/p' <<< "$*") # extract files parameters for `git show` command
-    enter_cmd="echo {} | $_forgit_extract_sha | xargs -I% ${FORGIT} diff %^! $files"
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         +s +m --tiebreak=index
-        --bind=\"enter:execute($enter_cmd)\"
+        --bind=\"enter:execute($FORGIT log_enter {} $files)\"
         --bind=\"ctrl-y:execute-silent(echo {} | $_forgit_extract_sha | ${FORGIT_COPY_CMD:-pbcopy})\"
         --preview=\"$FORGIT log_preview {} $files\"
         $FORGIT_LOG_FZF_OPTS
@@ -178,10 +184,16 @@ _forgit_diff_view() {
         "$FORGIT" exec_diff "${commits[@]}" -U"$diff_context" -- | $_forgit_diff_pager
 }
 
+_forgit_diff_enter() {
+    file=$1
+    commits=("${@:2}")
+    _forgit_diff_view "$file" "$_forgit_fullscreen_context" "${commits[@]}"
+}
+
 # git diff viewer
 _forgit_diff() {
     _forgit_inside_work_tree || return 1
-    local files opts commits repo get_files enter_cmd escaped_commits
+    local files opts commits escaped_commits
     [[ $# -ne 0 ]] && {
         if git rev-parse "$1" -- &>/dev/null ; then
             if [[ $# -gt 1 ]] && git rev-parse "$2" -- &>/dev/null; then
@@ -193,19 +205,6 @@ _forgit_diff() {
             files=("$@")
         fi
     }
-    repo="$(git rev-parse --show-toplevel)"
-    # Construct a null-terminated list of the filenames
-    # The input looks like one of these lines:
-    #   [R100]  file  ->  another file
-    #   [A]     file with spaces
-    #   [D]     oldfile
-    # And we transform it to this representation for further usage with "xargs -0":
-    #   file\0another file\0
-    #   file with spaces\0
-    #   oldfile\0
-    # We have to do a two-step sed -> tr pipe because OSX's sed implementation does
-    # not support the null-character directly.
-    get_files="echo {} | sed 's/.*] *//' | sed 's/  ->  /\\\n/' | tr '\\\n' '\\\0'"
     # Similar to the line above, but only gets a single file from a single line
     # Gets the new name of renamed files
     get_file="echo {} | sed 's/.*] *//' | sed 's/.*->  //'"
@@ -213,14 +212,12 @@ _forgit_diff() {
     # In order to support passing stashes as arguments to _forgit_diff, we have to
     # prevent fzf from interpreting this substring by escaping the opening bracket.
     # The string is evaluated a few subsequent times, so we need multiple escapes.
-    git_diff="git diff --color=always ${_forgit_diff_git_opts[*]} $escaped_commits"
-    enter_cmd="cd '$repo' && $get_files | xargs -0 $git_diff -U$_forgit_fullscreen_context -- | $_forgit_diff_pager"
     for commit in "${commits[@]}"; do
         escaped_commits+="'${commit//\{/\\\\\{}' "
     done
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
-        +m -0 --bind=\"enter:execute($enter_cmd | $_forgit_enter_pager)\"
+        +m -0 --bind=\"enter:execute($FORGIT diff_enter {} $escaped_commits | $_forgit_enter_pager)\"
         --preview=\"$FORGIT diff_view {} $_forgit_preview_context $escaped_commits\"
         --bind=\"alt-e:execute-silent($EDITOR \\\"\$\($get_file)\\\" >/dev/tty </dev/tty)+refresh-preview\"
         $FORGIT_DIFF_FZF_OPTS
@@ -900,6 +897,7 @@ private_commands=(
     "checkout_file_preview"
     "cherry_pick_from_branch_preview"
     "cherry_pick_preview"
+    "diff_enter"
     "file_preview"
     "ignore_preview"
     "revert_preview"
@@ -907,6 +905,7 @@ private_commands=(
     "stash_push_preview"
     "stash_show_preview"
     "log_preview"
+    "log_enter"
     "exec_diff"
     "diff_view"
 )