From 561f199505d13fb03641a389ce00d5d8e339e809 Mon Sep 17 00:00:00 2001
From: XeroOl <xerool@protonmail.com>
Date: Fri, 11 Jul 2025 23:36:05 -0500
Subject: [PATCH] hardcode in some argument counting exceptions

---
 flsproject.fnl         |  1 +
 src/fennel-ls/lint.fnl | 25 ++++++++++++++++++-------
 test/lint.fnl          | 13 ++++++++++++-
 3 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/flsproject.fnl b/flsproject.fnl
index 24381e7..d143b88 100644
--- a/flsproject.fnl
+++ b/flsproject.fnl
@@ -1,2 +1,3 @@
 {:lua-version "intersection"
+ :lints {:mismatched-argument-count true}
  :fennel-path "./?.fnl;./?/init.fnl;src/?.fnl;src/?/init.fnl;deps/?.fnl;deps/?/init.fnl"}
diff --git a/src/fennel-ls/lint.fnl b/src/fennel-ls/lint.fnl
index abf1831..ca47ace 100644
--- a/src/fennel-ls/lint.fnl
+++ b/src/fennel-ls/lint.fnl
@@ -9,6 +9,7 @@ the `file.diagnostics` field, filling it with diagnostics."
 (local message (require :fennel-ls.message))
 (local utils (require :fennel-ls.utils))
 (local navigate (require :fennel-ls.navigate))
+(local docs (require :fennel-ls.docs))
 (local dkjson (require :dkjson))
 
 (local lints {:definition []
@@ -295,9 +296,10 @@ the `file.diagnostics` field, filling it with diagnostics."
                {:indeterminate nil &as result}
                (case (?. (navigate.getmetadata server result) :fnl/arglist)
                  signature
-                 (let [number-of-args (- (length ast) 1)
+                 (let [number-of-args (- (length ast) (if (and (sym? (. ast 1)) (string.find (tostring (. ast 1)) ".:"))
+                                                        0 1))
                        passes-extra-args (and (not= 1 (length ast)) (possibly-multival? (. ast (length ast))))
-                       (number-of-params accepts-extra-params) (faccumulate [(last-required-argument vararg) nil
+                       (min-params infinite-params?) (faccumulate [(last-required-argument vararg) nil
                                                                              i (length signature) 1 -1]
                                                                  (let [s (tostring (. signature i))
                                                                        m (or (= s "...") (= s "&"))]
@@ -309,14 +311,23 @@ the `file.diagnostics` field, filling it with diagnostics."
                                                                          (not= (string.sub s 1 1) "?")
                                                                          i)
                                                                      (or vararg m))))
-                       number-of-params (or number-of-params 0)]
-                   (if (and (< number-of-args number-of-params) (not passes-extra-args))
+                       ;; exception: (- a b) only needs 1 argument
+                       ;; exception: (/ a b) only needs 1 argument
+                       min-params (if (= result (docs.get-builtin server :-)) 1
+                                      (= result (docs.get-builtin server :/)) 1
+                                      ;; exception: fn only needs one argument
+                                      ;; TODO Fennel 1.5.4+ has `fn`'s arglist fixed.
+                                      (= result (docs.get-builtin server :fn)) 1
+                                      (or min-params 0))
+                       ;; exception: (table.insert table item) can take a third argument
+                       max-params (if (= result (. (docs.get-global server :table) :fields :insert)) 3 (length signature))]
+                   (if (and (< number-of-args min-params) (not passes-extra-args))
                        {:range (message.ast->range server file ast)
-                        :message (.. "not enough args. my analysis of the signature says you need at least " number-of-params " arguments but I only see " number-of-args)
+                        :message (.. "not enough args. my analysis of the signature says you need at least " min-params " arguments but I only see " number-of-args)
                         :severity message.severity.WARN}
-                       (and (< (length signature) number-of-args) (not accepts-extra-params))
+                       (and (< max-params number-of-args) (not infinite-params?))
                        {:range (message.ast->range server file ast)
-                        :message (.. "too many args. my analysis of the signature says we ignore any arguments past " number-of-params " arguments but you've provided " number-of-args)
+                        :message (.. "too many args. my analysis of the signature says we ignore any arguments past " min-params " arguments but you've provided " number-of-args)
                         :severity message.severity.WARN})))))})
 
 (local lint-mt {:__tojson (fn [{: self} state] (dkjson.encode self state))
diff --git a/test/lint.fnl b/test/lint.fnl
index 4310a81..93ea25e 100644
--- a/test/lint.fnl
+++ b/test/lint.fnl
@@ -305,6 +305,16 @@
                    :end {:character 21 :line 0}}}])
   nil)
 
+(fn test-arg-count []
+  ;; methods
+  (assert-ok {:main.fnl "(let [f :hi] (f:byte))"
+              :flsproject.fnl "{:lints {:mismatched-argument-count true}}"})
+  (assert-ok {:main.fnl "(let [foo 10] (fn [] foo))"
+              :flsproject.fnl "{:lints {:mismatched-argument-count true}}"})
+  (assert-ok {:main.fnl "(fn [])"
+              :flsproject.fnl "{:lints {:mismatched-argument-count true}}"})
+  nil)
+
 ;; TODO lints:
 ;; duplicate keys in kv table
 ;; (tset <sym> <any>) --> (set (. <sym> <any>)) (might be wanted for compat?)
@@ -330,4 +340,5 @@
  : test-unpack-in-middle
  : test-op-with-no-arguments
  : test-empty-let
- : test-decreasing-comparison}
+ : test-decreasing-comparison
+ : test-arg-count}