Do not hide error messages when trying to return early (#318)

Most of forgits functions allow to invoke git directly when arguments were passed. In most of these functions we only return early when the git command that is executed returns successfully. This hides error messages from the user. As discussed with @carlfriedrich in #316, I've modified this behavior to also return early when the git command was not successful, so we're transparent about gits error messages and return values. This also fixes an infinite loop printing an error message when invalid arguments were passed to gsp. Because gbl and gclean allow passing arguments to the git command that is invoked when we don't return early, I've modified their behavior to only invoke git directly (and return early) in the case that non flag arguments were passed.
I've also modified gclean to use the -q flag instead of piping it's output to /dev/null.

bin/git-forgit

@@ -53,6 +53,18 @@ _forgit_previous_commit() {
     fi
 }
 
+_forgit_contains_non_flags() {
+    while (("$#")); do
+        case "$1" in
+        -*) shift ;;
+        *)
+            return 0
+            ;;
+        esac
+    done
+    return 1
+}
+
 # optional render emoji characters (https://github.com/wfxr/emoji-cli)
 hash emojify &>/dev/null && _forgit_emojify='|emojify'
 
@@ -157,7 +169,7 @@ _forgit_add() {
     local git_add changed unmerged untracked files opts preview extract
     git_add="git add $FORGIT_ADD_GIT_OPTS"
     # Add files if passed as arguments
-    [[ $# -ne 0 ]] && $git_add "$@" && git status -su && return
+    [[ $# -ne 0 ]] && { $git_add "$@" && git status -su; return $?; }
 
     changed=$(git config --get-color color.status.changed red)
     unmerged=$(git config --get-color color.status.unmerged red)
@@ -196,7 +208,7 @@ _forgit_reset_head() {
     _forgit_inside_work_tree || return 1
     local git_reset_head cmd files opts rootdir
     git_reset_head="git reset -q $FORGIT_RESET_HEAD_GIT_OPTS HEAD"
-    [[ $# -ne 0 ]] && $git_reset_head "$@" && git status --short && return
+    [[ $# -ne 0 ]] && { $git_reset_head "$@" && git status --short; return $?; }
     rootdir=$(git rev-parse --show-toplevel)
     cmd="git diff --staged --color=always -- $rootdir/{} | $_forgit_diff_pager "
     opts="
@@ -216,7 +228,7 @@ _forgit_stash_show() {
     _forgit_inside_work_tree || return 1
     local git_stash_show git_stash_list cmd opts
     git_stash_show="git stash show --color=always --ext-diff"
-    [[ $# -ne 0 ]] && $git_stash_show "$@" && return
+    [[ $# -ne 0 ]] && { $git_stash_show "$@"; return $?; }
     git_stash_list="git stash list $FORGIT_STASH_SHOW_GIT_OPTS"
     cmd="echo {} |cut -d: -f1 |xargs -I% $git_stash_show % |$_forgit_diff_pager"
     opts="
@@ -249,7 +261,7 @@ _forgit_stash_push() {
             # ignore -u as it's used implicitly
             -u|--include-untracked) shift ;;
             # pass to git directly when encountering anything else
-            *) $git_stash_push "${args[@]}" && return $?
+            *) $git_stash_push "${args[@]}"; return $?
         esac
     done
     local opts preview files
@@ -274,7 +286,7 @@ _forgit_stash_push() {
 # git clean selector
 _forgit_clean() {
     _forgit_inside_work_tree || return 1
-    [[ $# -ne 0 ]] && git clean "$@" &>/dev/null && return 0
+    _forgit_contains_non_flags "$@" && { git clean -q "$@"; return $?; }
     local git_clean files opts
     git_clean="git clean $FORGIT_CLEAN_GIT_OPTS"
     opts="
@@ -522,7 +534,7 @@ _forgit_branch_delete() {
     _forgit_inside_work_tree || return 1
     local git_branch preview opts cmd branches
     git_branch="git branch $FORGIT_BRANCH_DELETE_GIT_OPTS"
-    [[ $# -ne 0 ]] && $git_branch -D "$@" && return
+    [[ $# -ne 0 ]] && { $git_branch -D "$@"; return $?; }
     preview="git log {1} $_forgit_log_preview_options"
 
     opts="
@@ -582,7 +594,7 @@ _forgit_blame() {
     _forgit_inside_work_tree || return 1
     local git_blame opts flags preview file
     git_blame="git blame $FORGIT_BLAME_GIT_OPTS"
-    [[ $# -ne 0 ]] && $git_blame "$@" && return 0
+    _forgit_contains_non_flags "$@" && { $git_blame "$@"; return $?; }
     opts="
         $FORGIT_FZF_DEFAULT_OPTS
         $FORGIT_BLAME_FZF_OPTS