Allow fish comp to support trailing empty lines (#1284)

Some programs may output extra empty lines after the directive.
Those lines must be ignored for fish shell completion to work.
zsh and bash are not impacted.

Signed-off-by: Marc Khouzam <marc.khouzam@montreal.ca>
Co-authored-by: Johannes Altmanninger <aclopte@gmail.com>

Co-authored-by: Johannes Altmanninger <aclopte@gmail.com>

fish_completions.go

@@ -53,6 +53,19 @@ function __%[1]s_perform_completion
     __%[1]s_debug "Calling $requestComp"
 
     set results (eval $requestComp 2> /dev/null)
+
+    # Some programs may output extra empty lines after the directive.
+    # Let's ignore them or else it will break completion.
+    # Ref: https://github.com/spf13/cobra/issues/1279
+    for line in $results[-1..1]
+        if test (string trim -- $line) = ""
+            # Found an empty line, remove it
+            set results $results[1..-2]
+        else
+            # Found non-empty line, we have our proper output
+            break
+        end
+    end
     set comps $results[1..-2]
     set directiveLine $results[-1]