Add lint for (values) in non-tail position of a call

README.md

@@ -15,8 +15,6 @@ make && sudo make install # to install into /usr/local/bin
 make && make install PREFIX=$HOME # if you have ~/bin on your $PATH
 ```
 
-For now, the only way to install is to build from source, but I plan on adding fennel-ls to luarocks soon.
-
 ### NixOS
 
 If you are using NixOS, you may use the included `/flake.nix` or `/default.nix`

src/fennel-ls/compiler.fnl

@@ -278,7 +278,7 @@ identifiers are declared / referenced in which places."
     (let [macro-file? (= (file.text:sub 1 24) ";; fennel-ls: macro-file")
           plugin
           {:name "fennel-ls"
-           :versions ["1.4.1"]
+           :versions ["1.4.1" "1.5.0"]
            : symbol-to-expression
            : call
            : destructure

src/fennel-ls/diagnostics.fnl

@@ -6,6 +6,19 @@ the `file.diagnostics` field, filling it with diagnostics."
 (local language (require :fennel-ls.language))
 (local message (require :fennel-ls.message))
 (local utils (require :fennel-ls.utils))
+(local {:scopes {:global {: specials}}}
+  (require :fennel.compiler))
+
+(local ops {"+" 1 "-" 1 "*" 1 "/" 1 "//" 1 "%" 1 "^" 1 ">" 1 "<" 1 ">=" 1 "<=" 1 "=" 1 "not=" 1 ".." 1 "." 1 "and" 1 "or" 1 "band" 1 "bor" 1 "bxor" 1 "bnot" 1 "lshift" 1 "rshift" 1})
+(fn special? [item]
+  (and (sym? item)
+       (. specials (tostring item))
+       item))
+
+(fn op? [item]
+  (and (sym? item)
+       (. ops (tostring item))
+       item))
 
 (λ unused-definition [self file symbol definition]
   "local variable that is defined but not used"
@@ -49,12 +62,10 @@ the `file.diagnostics` field, filling it with diagnostics."
          :code 303
          :codeDescription "unnecessary-method"}))))
 
-(local ops {"+" 1 "-" 1 "*" 1 "/" 1 "//" 1 "%" 1 "^" 1 ">" 1 "<" 1 ">=" 1 "<=" 1 "=" 1 "not=" 1 ".." 1 "." 1 "and" 1 "or" 1 "band" 1 "bor" 1 "bxor" 1 "bnot" 1 "lshift" 1 "rshift" 1})
 (λ bad-unpack [self file op call]
   "an unpack call leading into an operator"
   (let [last-item (. call (length call))]
-    (if (and (sym? op)
+    (if (and (op? op)
-             (. ops (tostring op))
              ;; last item is an unpack call
              (list? last-item)
              (or (sym? (. last-item 1) :unpack)
@@ -83,8 +94,7 @@ the `file.diagnostics` field, filling it with diagnostics."
 (local op-identity-value {:+ 0 :* 1 :and true :or false :band -1 :bor 0 :.. ""})
 (λ op-with-no-arguments [self file op call]
   "A call like (+) that could be replaced with a literal"
-  (if (and (sym? op)
+  (if (and (op? op)
-           (. ops (tostring op))
            (not (. call 2))
            (. file.lexical call)
            (not= nil (. op-identity-value (tostring op))))
@@ -94,22 +104,48 @@ the `file.diagnostics` field, filling it with diagnostics."
      :code 306
      :codeDescription "op-with-no-arguments"}))
 
+(λ multival-in-middle-of-call [self file fun call arg index]
+  "generally, values and unpack are signs that the user is trying to do
+  something with multiple values. However, multiple values will get
+  \"adjusted\" to one value if they don't come at the end of the call."
+  (if (and (not (and (special? fun) (not (op? fun))))
+           (not= index (length call))
+           (list? arg)
+           (or (sym? (. arg 1) :values)
+               (sym? (. arg 1) :unpack)
+               (sym? (. arg 1) :_G.unpack)
+               (sym? (. arg 1) :table.unpack)))
+    {:range (message.ast->range self file arg)
+     :message (.. "bad " (tostring (. arg 1)) " call: only the first value of the multival will be used")
+     :severity message.severity.WARN
+     :code 307
+     :codeDescription "bad-unpack"}))
+
 (λ check [self file]
   "fill up the file.diagnostics table with linting things"
   (let [checks self.configuration.checks
         diagnostics file.diagnostics]
-    ;; definition diagnostics
+
+    ;; definition lints
     (each [symbol definition (pairs file.definitions)]
       (if checks.unused-definition (table.insert diagnostics (unused-definition self file symbol definition)))
       (if checks.var-never-set     (table.insert diagnostics (var-never-set     self file symbol definition))))
 
-    ;; call diagnostics
+    ;; call lints
-    ;; all non-macro calls. This only covers the macroexpanded world
+    ;; all non-macro calls. This only covers specials and function calls.
     (each [[head &as call] (pairs file.calls)]
       (when head
         (if checks.bad-unpack           (table.insert diagnostics (bad-unpack           self file head call)))
         (if checks.unnecessary-method   (table.insert diagnostics (unnecessary-method   self file head call)))
-        (if checks.op-with-no-arguments (table.insert diagnostics (op-with-no-arguments self file head call)))))
+        (if checks.op-with-no-arguments (table.insert diagnostics (op-with-no-arguments self file head call)))
+
+        ;; argument lints
+        ;; every argument to a special or a function call
+        ;; TODO: This may be changed to run for function calls, but not special calls.
+        ;; I'll wait till we have more lints in here to see if it needs to change.
+        (for [index 2 (length call)]
+          (let [arg (. call index)]
+            (if checks.multival-in-middle-of-call (table.insert diagnostics (multival-in-middle-of-call self file head call arg index)))))))
 
     (if checks.unknown-module-field
       (unknown-module-field self file))))

src/fennel-ls/state.fnl

@@ -99,7 +99,8 @@ entire fennel-ls project is referring to the same object."
             :unnecessary-method (option true)
             :bad-unpack (option true)
             :var-never-set (option true)
-            :op-with-no-arguments (option true)}
+            :op-with-no-arguments (option true)
+            :multival-in-middle-of-call (option true)}
    :extra-globals (option "")})
 
 (λ make-configuration [?c]

test/diagnostic-test.fnl

@@ -264,7 +264,34 @@
                    (match v
                      {:code 304}
                      v)
-                   (v.message:find "table.concat"))))))))
+                   (v.message:find "table.concat")))))))
+
+  (it "tells me not to use values in the middle"
+    (let [self (create-client)
+          responses (self:open-file! filename "(+ 1 2 3 (values 4 5) 6)")]
+      (match responses
+        [{:params {: diagnostics}}]
+        (is (find [_ v (ipairs diagnostics)]
+             (and
+               (match v
+                 {:code 307}
+                 v)
+               (v.message:find "values")))))))
+
+  (it "doesn't trigger the values warning (code 307) in a statement context"
+    (let [self (create-client)
+          responses (self:open-file! filename "(let [x 10] (values 4 5) x)")]
+      (match responses
+        [{:params {: diagnostics}}]
+        (is
+          (not
+            (find [_ v (ipairs diagnostics)]
+              (and
+                (match v
+                  {:code 307}
+                  v)
+                (v.message:find "values")))))))))
+
 
 ;; TODO lints:
 ;; unnecessary (do) in body position