Add 'as message' syntax for todo and panic (#64)

grammar.js

@@ -370,8 +370,18 @@ module.exports = grammar({
         optional(field("arguments", $.arguments))
       ),
     todo: ($) =>
-      seq("todo", optional(seq("(", field("message", $.string), ")"))),
-    panic: (_$) => seq("panic"),
+      seq(
+        "todo",
+        optional(
+          choice(
+            // DEPRECATED: The 'as' syntax was introduced in v0.30.
+            seq("(", field("message", $.string), ")"),
+            seq("as", field("message", $._expression))
+          )
+        )
+      ),
+    panic: ($) =>
+      seq("panic", optional(seq("as", field("message", $._expression)))),
     tuple: ($) => seq("#", "(", optional(series_of($._expression, ",")), ")"),
     list: ($) =>
       seq(

test/corpus/functions.txt

@@ -239,10 +239,11 @@ fn funcall() {
   myfun()
 }
 fn unfinished() {
-  todo("Finish me!")
+  todo as "Finish me!"
 }
 fn do_panic() {
   panic
+  panic as "aaaah!"
 }
 fn tuple(x) {
   #(x, 1)
@@ -376,7 +377,10 @@ fn field_access(x) {
     name: (identifier)
     parameters: (function_parameters)
     body: (function_body
-      (panic)))
+      (panic)
+      (panic
+        message: (string
+          (quoted_content)))))
   (function
     name: (identifier)
     parameters: (function_parameters

test/highlight/expressions.gleam

@@ -10,3 +10,7 @@ case "12345" {
    -x
 // ^ operator
 //  ^ variable
+panic as "aaah!"
+// <- keyword
+//    ^ keyword
+//         ^ string