Format '--check' errors so that tooling can detect them

src/fennel-ls.fnl

@@ -20,7 +20,7 @@
       (let [file (files.get-by-uri server (.. "file://" filename))]
         (lint.check server file)
         (each [_ {: message :range {: start}} (ipairs file.diagnostics)]
-          (print (: "%s:%s:%s %s" :format filename
+          (print (: "%s:%s:%s: %s" :format filename
                     ;; LSP line numbers are zero-indexed, but Emacs and Vim both use
                     ;; 1-indexing for this.
                     (+ (or start.line 0) 1) (or start.character "?") message)))

test/check.fnl

@@ -0,0 +1,18 @@
+(local faith (require :faith))
+
+;; TODO refactor fennel-ls.check to avoid running end-to-end
+;; (but keep/write at least some end-to-end tests)
+(fn test-check []
+  (let [input-file-name (os.tmpname)]
+    (doto (io.open input-file-name :w)
+      (: :write "(local x 1)")
+      (: :close))
+    (let [output-file (io.popen (.. "./fennel-ls --check "
+                                    input-file-name)
+                                :r)]
+      (faith.= (.. input-file-name ":1:7: unused definition: x\n")
+               (output-file:read :*a) )
+      (os.remove input-file-name))
+    nil))
+
+{: test-check}

test/init.fnl

@@ -24,4 +24,5 @@
    :test.lint
    :test.code-action
    :test.rename
-   :test.misc])
+   :test.misc
+   :test.check])