Add empty-do hint

src/fennel-ls/lint.fnl

@@ -277,6 +277,33 @@ You can read more about how to add lints in docs/linting.md"
                        :changes [{:range (message.ast->range server file ast)
                                   :newText (view (. ast 2))}]}}))})
 
+(add-lint :empty-do
+  {:what-it-does
+   "Warns about `do` with no body."
+   :why-care?
+   "Using `do` with no body has no effect."
+   :example
+   "```fnl
+    (do)
+    ```
+
+    Instead, use:
+    ```fnl
+    ;; nothing
+    ```"
+   :since "0.2.2-dev"
+   :type :special-call
+   :impl (fn [server file ast]
+           (case ast
+             (where [do* & body]
+                    (sym? do* :do)
+                    (not (next body)))
+             {: ast
+              :message "remove do with no body"
+              :fix #{:title "Remove (do)"
+                     :changes [{:range (message.ast->range server file ast)
+                                :newText ""}]}}))})
+
 (add-lint :redundant-do
   {:what-it-does
    "Identifies redundant `do` blocks within implicit do forms like `fn`, `let`, etc."

test/lint.fnl

@@ -222,6 +222,17 @@
                    :end {:character 8 :line 0}}}])
   nil)
 
+(fn test-empty-do []
+  ;; good do
+  (assert-ok "(do (print 1) 2)")
+  ;; unnecessary one
+  (check "(do (do) 1 2)"
+         [{:code :empty-do
+           :message "remove do with no body"
+           :range {:start {:character 4 :line 0}
+                   :end {:character 8 :line 0}}}])
+  nil)
+
 (fn test-redundant-do []
   ;; good do
   (assert-ok "(case 134 x (do (print :x x) 11))")
@@ -403,6 +414,7 @@
  : test-unnecessary-method
  : test-unnecessary-tset
  : test-unnecessary-unary
+ : test-empty-do
  : test-redundant-do
  : test-unset-var
  : test-match-should-case