Implement completer for "del".

This fixes #1774.

pkg/edit/complete/complete_test.go

@@ -206,6 +206,16 @@ func TestComplete(t *testing.T) {
 					ci("local-var1"), ci("local-var2"),
 				},
 			}),
+		// "del" has a similar completer.
+		Args(cb("del "), ev, cfg).Rets(
+			&Result{
+				Name: "argument", Replace: r(4, 4),
+				Items: []modes.CompletionItem{
+					ci("local-fn1~"), ci("local-fn2~"),
+					ci("local-ns1:"), ci("local-ns2:"),
+					ci("local-var1"), ci("local-var2"),
+				},
+			}),
 
 		// Complete commands at an empty buffer, generating special forms,
 		// externals, functions, namespaces and variable assignments.

pkg/edit/complete/generators.go

@@ -63,6 +63,16 @@ func generateArgs(args []string, ev *eval.Evaler, p np.Path, cfg Config) ([]RawI
 			items = append(items, noQuoteItem(sigil+parse.QuoteVariableName(ns+varname)))
 		})
 		return items, nil
+	case "del":
+		// This partially duplicates eachVariableInNs with ns = "", but we don't
+		// offer builtin variables.
+		var items []RawItem
+		addItem := func(varname string) {
+			items = append(items, noQuoteItem(parse.QuoteVariableName(varname)))
+		}
+		ev.Global().IterateKeysString(addItem)
+		eachDefinedVariable(p[len(p)-1], p[0].Range().From, addItem)
+		return items, nil
 	}
 
 	return cfg.ArgGenerator(args)