Warn when function is not modified by the editor after calling `funce…

…d` (#3961)

* Check whether tmp file was modified in `funced`

* More idiomatic error messages

* Store the checksum in a local variable

* MD5 function supporting both GNU and BSD

* Use `else if` in MD5 function

* Use `string` builtin instead of `cut`

share/functions/funced.fish

@@ -1,3 +1,16 @@
+function __funced_md5
+    if type -q md5sum
+        # GNU systems
+        echo (md5sum $argv[1] | string split ' ')[1]
+        return 0
+    else if type -q md5
+        # BSD systems
+        md5 -q $argv[1]
+        return 0
+    end
+    return 1
+end
+
 function funced --description 'Edit function definition'
     set -l editor
     # Check VISUAL first since theoretically EDITOR could be ed
@@ -39,8 +52,7 @@ function funced --description 'Edit function definition'
 
     if test (count $funcname) -ne 1
         set_color red
-        _ "funced: You must specify one function name
-"
+        echo (_ "funced: You must specify one function name")
         set_color normal
         return 1
     end
@@ -58,8 +70,7 @@ function funced --description 'Edit function definition'
         set -l editor_cmd
         eval set editor_cmd $editor
         if not type -q -f "$editor_cmd[1]"
-            _ "funced: The value for \$EDITOR '$editor' could not be used because the command '$editor_cmd[1]' could not be found
-    "
+            echo (_ "funced: The value for \$EDITOR '$editor' could not be used because the command '$editor_cmd[1]' could not be found")
             set editor fish
         end
     end
@@ -102,14 +113,25 @@ function funced --description 'Edit function definition'
     else
         echo $init >$tmpname
     end
+
     # Repeatedly edit until it either parses successfully, or the user cancels
     # If the editor command itself fails, we assume the user cancelled or the file
     # could not be edited, and we do not try again
     while true
+        set -l checksum (__funced_md5 "$tmpname")
+
         if not eval $editor $tmpname
-            _ "Editing failed or was cancelled"
-            echo
+            echo (_ "Editing failed or was cancelled")
         else
+            # Verify the checksum (if present) to detect potential problems
+            # with the editor command
+            if set -q checksum[1]
+                set -l new_checksum (__funced_md5 "$tmpname")
+                if test "$new_checksum" = "$checksum"
+                    echo (_ "Editor exited but the function was not modified")
+                end
+            end
+
             if not source $tmpname
                 # Failed to source the function file. Prompt to try again.
                 echo # add a line between the parse error and the prompt
@@ -121,12 +143,12 @@ function funced --description 'Edit function definition'
                 if not contains $repeat n N no NO No nO
                     continue
                 end
-                _ "Cancelled function editing"
-                echo
+                echo (_ "Cancelled function editing")
             end
         end
         break
     end
+
     set -l stat $status
     rm $tmpname >/dev/null
     and rmdir $tmpdir >/dev/null