fix(checker): raise error if array type cannot be inferred

CHANGELOG.md

@@ -15,6 +15,7 @@ _unreleased_
 
 ### Type Checks
 - Ensure function parameter type exists
+- Raise error if array type cannot be inferred
 - Properly check return type of `array.last()`
 
 ### C Backend

lib/bait/checker/expr.bt

@@ -75,6 +75,10 @@ fun (mut c Checker) array_init(mut node ast.ArrayInit) ast.Type {
 	if node.exprs.length == 0 {
 		// Typeless array init
 		if node.elem_type == ast.PLACEHOLDER_TYPE {
+			if c.expected_type == ast.VOID_TYPE {
+				c.error('cannot infer type of empty array', node.pos)
+			}
+
 			node.typ = c.expected_type
 			return node.typ
 		}

tests/out/error/array/cannot_infer.in.bt

@@ -0,0 +1 @@
+const FOO := []

tests/out/error/array/cannot_infer.out

@@ -0,0 +1 @@
+tests/out/error/array/cannot_infer.in.bt:1:13 error: cannot infer type of empty array