From 6e483e795ceea735e24b5987b8585a860831db79 Mon Sep 17 00:00:00 2001
From: Gusztav Szikszai <guszti5@hotmail.com>
Date: Sun, 3 Jun 2018 11:19:33 +0200
Subject: [PATCH] Only allow negating booleans.

---
 spec/formatters/negated_expression          |  4 ++--
 spec/type_checking/negated_expression       | 11 +++++++++++
 src/formatters/negated_expression.cr        |  1 +
 src/messages/negated_expression_not_bool.cr | 11 +++++++++++
 src/type_checkers/negated_expression.cr     | 12 +++++++++++-
 5 files changed, 36 insertions(+), 3 deletions(-)
 create mode 100644 spec/type_checking/negated_expression
 create mode 100644 src/messages/negated_expression_not_bool.cr

diff --git a/spec/formatters/negated_expression b/spec/formatters/negated_expression
index adc51f1e1..655b8d39c 100644
--- a/spec/formatters/negated_expression
+++ b/spec/formatters/negated_expression
@@ -1,11 +1,11 @@
 module Test {
   fun test : Bool {
-    !!!!!"fun" && !!!![1] && !1
+    !!!!!true && !!!!false && !false
   }
 }
 --------------------------------------------------------------------------------
 module Test {
   fun test : Bool {
-    !"fun" && !![1] && !1
+    !true && !!false && !false
   }
 }
diff --git a/spec/type_checking/negated_expression b/spec/type_checking/negated_expression
new file mode 100644
index 000000000..5800cd1f4
--- /dev/null
+++ b/spec/type_checking/negated_expression
@@ -0,0 +1,11 @@
+module Test {
+  fun test : Bool {
+    !false
+  }
+}
+--------------------------------------------------------NegatedExpressionNotBool
+module Test {
+  fun test : Bool {
+    !"asd"
+  }
+}
diff --git a/src/formatters/negated_expression.cr b/src/formatters/negated_expression.cr
index 049986299..ec258b879 100644
--- a/src/formatters/negated_expression.cr
+++ b/src/formatters/negated_expression.cr
@@ -3,6 +3,7 @@ module Mint
     def format(node : Ast::NegatedExpression) : String
       expression =
         format node.expression
+
       "#{node.negations}#{expression}"
     end
   end
diff --git a/src/messages/negated_expression_not_bool.cr b/src/messages/negated_expression_not_bool.cr
new file mode 100644
index 000000000..681521bd9
--- /dev/null
+++ b/src/messages/negated_expression_not_bool.cr
@@ -0,0 +1,11 @@
+message NegatedExpressionNotBool do
+  title "Type Error"
+
+  block do
+    text "A negated expressions expression must evaluate to bool."
+  end
+
+  was_expecting_type expected, got
+
+  snippet node
+end
diff --git a/src/type_checkers/negated_expression.cr b/src/type_checkers/negated_expression.cr
index a6f0745ab..9553afc60 100644
--- a/src/type_checkers/negated_expression.cr
+++ b/src/type_checkers/negated_expression.cr
@@ -1,7 +1,17 @@
 module Mint
   class TypeChecker
+    type_error NegatedExpressionNotBool
+
     def check(node : Ast::NegatedExpression) : Type
-      BOOL
+      expression =
+        check node.expression
+
+      raise NegatedExpressionNotBool, {
+        "got"      => expression,
+        "expected" => BOOL,
+      } unless Comparer.compare(BOOL, expression)
+
+      expression
     end
   end
 end