[Search git status] beautify header

Put a border around the diff type header created using ASCII art to make it stand out more.
Pass --no-prefix to git diff to slightly shorten the diff header.

functions/_fzf_preview_changed_file.fish

@@ -14,14 +14,17 @@ function _fzf_preview_changed_file --description "Show the untracked, staged, an
         _fzf_report_diff_type Untracked
         _fzf_preview_file $path
     else
+        # no-prefix because the file is always being compared to itself so is unecessary
+        set diff_opts --color=always --no-prefix
+
         if test $index_status != ' '
             _fzf_report_diff_type Staged
-            git diff --staged --color=always -- $path
+            git diff --staged $diff_opts -- $path
         end
 
         if test $working_tree_status != ' '
             _fzf_report_diff_type Unstaged
-            git diff --color=always -- $path
+            git diff $diff_opts -- $path
         end
     end
 end

functions/_fzf_report_diff_type.fish

@@ -1,6 +1,16 @@
 # helper for _fzf_preview_changed_file
-function _fzf_report_diff_type --argument-names diff_type --description "Print a distinct colored header."
-    set_color --underline yellow
-    echo -e === $diff_type ===\n
+# prints out something like
+# +--------+
+# | Staged |
+# +--------+
+function _fzf_report_diff_type --argument-names diff_type --description "Print a distinct colored header meant to preface a git patch."
+    # number of "-" to draw is the length of the string to box + 2 for padding
+    set repeat_count (math 2 + (string length $diff_type))
+    set horizontal_border +(string repeat --count $repeat_count -)+
+
+    set_color yellow
+    echo $horizontal_border
+    echo "| $diff_type |"
+    echo $horizontal_border
     set_color normal
 end

tests/preview_changed_file/deleted_in_working.fish

@@ -2,5 +2,6 @@ mock git diff "echo \$argv"
 set file dir/file.txt
 
 set output (_fzf_preview_changed_file " D $file")
-contains -- "--color=always -- $file" $output && not string match -- "*--staged*" $output
+
+contains -- "| Unstaged |" $output && not contains "| Staged |" $output
 @test "only shows unstaged changes if file was only deleted in working tree" $status -eq 0

tests/preview_changed_file/modified_in_both.fish

@@ -2,5 +2,5 @@ mock git diff "echo \$argv"
 set file dir/file.txt
 set output (_fzf_preview_changed_file "MM $file")
 
-contains -- "--staged --color=always -- $file" $output && contains -- "--color=always -- $file" $output
+contains -- "| Unstaged |" $output && contains "| Staged |" $output
 @test "shows staged and unstaged changes if the file is modified in both places" $status -eq 0