sample_prompts/robbyrussell: Clean

- Remove use of `eval`
- Use `git rev-parse` instead of `git status` as its faster,
- especially in large repos. (in qt5: 600ms vs 1ms)

- Use return status instead of test -n

This should change nothing about the output.

share/tools/web_config/sample_prompts/robbyrussell.fish

@@ -22,7 +22,7 @@ function fish_prompt
         function _is_git_repo
             type -q git
             or return 1
-            git status -s >/dev/null 2>/dev/null
+            git rev-parse --git-dir >/dev/null 2>&1
         end
 
         function _hg_branch_name
@@ -40,19 +40,22 @@ function fish_prompt
         end
 
         function _repo_branch_name
-            eval "_$argv[1]_branch_name"
+            _$argv[1]_branch_name
         end
 
         function _is_repo_dirty
-            eval "_is_$argv[1]_dirty"
+            _is_$argv[1]_dirty
         end
 
         function _repo_type
             if _is_hg_repo
                 echo 'hg'
+                return 0
             else if _is_git_repo
                 echo 'git'
+                return 0
             end
+            return 1
         end
     end
 
@@ -75,8 +78,7 @@ function fish_prompt
 
     set -l cwd $cyan(basename (prompt_pwd))
 
-    set -l repo_type (_repo_type)
-    if [ $repo_type ]
+    if set -l repo_type (_repo_type)
         set -l repo_branch $red(_repo_branch_name $repo_type)
         set repo_info "$blue $repo_type:($repo_branch$blue)"